[PATCH v3 00/16] Make the user mode driver code a better citizen

STALE2247d

Revision v3 of 3 in this series.

23 messages, 6 authors, 2020-07-12 · open the first message on its own page

[PATCH v3 00/16] Make the user mode driver code a better citizen

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:45:19

This is the third round of my changeset to split the user mode driver
code from the user mode helper code, and to make the code use common
facilities to get things done instead of recreating them just
for the user mode driver code.

I have split the changes into small enough pieces so they should be
easily readable and testable.

The changes lean into the preexisting interfaces in the kernel and
remove special cases for user mode driver code in favor of solutions
that don't need special cases.  This results in smaller code with fewer
bugs.

At a practical level this removes the maintenance burden of the user
mode drivers from the user mode helper code and from exec as the special
cases are removed.

Similarly the LSM interaction bugs are fixed by not having unnecessary
special cases for user mode drivers.

I have tested thes changes by booting with the code compiled in and
by killing "bpfilter_umh" and "running iptables -vnL" to restart
the userspace driver, also by running "while true; do iptables -L;rmmod
bpfilter; done" to verify the module load and unload work properly.

I have compiled tested each change with and without CONFIG_BPFILTER
enabled.

From v2 to v3 I have made two siginficant changes.
- I factored thread_group_exit out of pidfd_poll to allow the test
  to be used by the bpfilter code.
- I renamed umd.c and umd.h to usermode_driver.c and usermode_driver.h
  respectively.

I made a few very small changes from v1 to v2:
- Updated the function name in a comment when the function is renamed
- Moved some more code so that the the !CONFIG_BPFILTER case continues
  to compile when I moved the code into umd.c
- A fix for the module loading case to really flush the file descriptor.
- Removed split_argv entirely from fork_usermode_driver.
  There was nothing to split so it was just confusing.

Please let me know if you see any bugs.  Once the code review is
finished I plan to place the code in a non-rebasing branch
so I can pull it into my tree and so it can also be pulled into
the bpf-next tree.

v1: https://lkml.kernel.org/r/87pn9mgfc2.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87bll17ili.fsf_-_@x220.int.ebiederm.org

Eric W. Biederman (16):
      umh: Capture the pid in umh_pipe_setup
      umh: Move setting PF_UMH into umh_pipe_setup
      umh: Rename the user mode driver helpers for clarity
      umh: Remove call_usermodehelper_setup_file.
      umh: Separate the user mode driver and the user mode helper support
      umd: For clarity rename umh_info umd_info
      umd: Rename umd_info.cmdline umd_info.driver_name
      umd: Transform fork_usermode_blob into fork_usermode_driver
      umh: Stop calling do_execve_file
      exec: Remove do_execve_file
      bpfilter: Move bpfilter_umh back into init data
      umd: Track user space drivers with struct pid
      exit: Factor thread_group_exited out of pidfd_poll
      bpfilter: Take advantage of the facilities of struct pid
      umd: Remove exit_umh
      umd: Stop using split_argv

 fs/exec.c                        |  38 ++------
 include/linux/binfmts.h          |   1 -
 include/linux/bpfilter.h         |   7 +-
 include/linux/sched.h            |   9 --
 include/linux/sched/signal.h     |   2 +
 include/linux/umh.h              |  15 ----
 include/linux/usermode_driver.h  |  18 ++++
 kernel/Makefile                  |   1 +
 kernel/exit.c                    |  25 +++++-
 kernel/fork.c                    |   6 +-
 kernel/umh.c                     | 171 +-----------------------------------
 kernel/usermode_driver.c         | 182 +++++++++++++++++++++++++++++++++++++++
 net/bpfilter/bpfilter_kern.c     |  38 ++++----
 net/bpfilter/bpfilter_umh_blob.S |   2 +-
 net/ipv4/bpfilter/sockopt.c      |  20 +++--
 15 files changed, 275 insertions(+), 260 deletions(-)


Eric W. Biederman (15):
      umh: Capture the pid in umh_pipe_setup
      umh: Move setting PF_UMH into umh_pipe_setup
      umh: Rename the user mode driver helpers for clarity
      umh: Remove call_usermodehelper_setup_file.
      umh: Separate the user mode driver and the user mode helper support
      umd: For clarity rename umh_info umd_info
      umd: Rename umd_info.cmdline umd_info.driver_name
      umd: Transform fork_usermode_blob into fork_usermode_driver
      umh: Stop calling do_execve_file
      exec: Remove do_execve_file
      bpfilter: Move bpfilter_umh back into init data
      umd: Track user space drivers with struct pid
      bpfilter: Take advantage of the facilities of struct pid
      umd: Remove exit_umh
      umd: Stop using split_argv

 fs/exec.c                        |  38 ++------
 include/linux/binfmts.h          |   1 -
 include/linux/bpfilter.h         |   7 +-
 include/linux/sched.h            |   9 --
 include/linux/umd.h              |  18 ++++
 include/linux/umh.h              |  15 ----
 kernel/Makefile                  |   1 +
 kernel/exit.c                    |   1 -
 kernel/umd.c                     | 182 +++++++++++++++++++++++++++++++++++++++
 kernel/umh.c                     | 171 +-----------------------------------
 net/bpfilter/bpfilter_kern.c     |  38 ++++----
 net/bpfilter/bpfilter_umh_blob.S |   2 +-
 net/ipv4/bpfilter/sockopt.c      |  20 +++--
 13 files changed, 248 insertions(+), 255 deletions(-)

[PATCH v3 01/16] umh: Capture the pid in umh_pipe_setup

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:47:32

The pid in struct subprocess_info is only used by umh_clean_and_save_pid to
write the pid into umh_info.

Instead always capture the pid on struct umh_info in umh_pipe_setup, removing
code that is specific to user mode drivers from the common user path of
user mode helpers.

v1: https://lkml.kernel.org/r/87h7uygf9i.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/875zb97iix.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/umh.h | 1 -
 kernel/umh.c        | 5 ++---
 2 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/include/linux/umh.h b/include/linux/umh.h
index 0c08de356d0d..aae16a0ebd0f 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -25,7 +25,6 @@ struct subprocess_info {
 	struct file *file;
 	int wait;
 	int retval;
-	pid_t pid;
 	int (*init)(struct subprocess_info *info, struct cred *new);
 	void (*cleanup)(struct subprocess_info *info);
 	void *data;
diff --git a/kernel/umh.c b/kernel/umh.c
index 79f139a7ca03..c2a582b3a2bf 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -102,7 +102,6 @@ static int call_usermodehelper_exec_async(void *data)
 
 	commit_creds(new);
 
-	sub_info->pid = task_pid_nr(current);
 	if (sub_info->file) {
 		retval = do_execve_file(sub_info->file,
 					sub_info->argv, sub_info->envp);
@@ -468,6 +467,7 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 
 	umh_info->pipe_to_umh = to_umh[1];
 	umh_info->pipe_from_umh = from_umh[0];
+	umh_info->pid = task_pid_nr(current);
 	return 0;
 }
 
@@ -476,13 +476,12 @@ static void umh_clean_and_save_pid(struct subprocess_info *info)
 	struct umh_info *umh_info = info->data;
 
 	/* cleanup if umh_pipe_setup() was successful but exec failed */
-	if (info->pid && info->retval) {
+	if (info->retval) {
 		fput(umh_info->pipe_to_umh);
 		fput(umh_info->pipe_from_umh);
 	}
 
 	argv_free(info->argv);
-	umh_info->pid = info->pid;
 }
 
 /**
-- 
2.25.0

[PATCH v3 02/16] umh: Move setting PF_UMH into umh_pipe_setup

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:47:39

I am separating the code specific to user mode drivers from the code
for ordinary user space helpers.  Move setting of PF_UMH from
call_usermodehelper_exec_async which is core user mode helper code
into umh_pipe_setup which is user mode driver code.

The code is equally as easy to write in one location as the other and
the movement minimizes the impact of the user mode driver code on the
core of the user mode helper code.

Setting PF_UMH unconditionally is harmless as an action will only
happen if it is paired with an entry on umh_list.

v1: https://lkml.kernel.org/r/87bll6gf8t.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87zh8l63xs.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 kernel/umh.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/kernel/umh.c b/kernel/umh.c
index c2a582b3a2bf..e6b9d6636850 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -102,12 +102,10 @@ static int call_usermodehelper_exec_async(void *data)
 
 	commit_creds(new);
 
-	if (sub_info->file) {
+	if (sub_info->file)
 		retval = do_execve_file(sub_info->file,
 					sub_info->argv, sub_info->envp);
-		if (!retval)
-			current->flags |= PF_UMH;
-	} else
+	else
 		retval = do_execve(getname_kernel(sub_info->path),
 				   (const char __user *const __user *)sub_info->argv,
 				   (const char __user *const __user *)sub_info->envp);
@@ -468,6 +466,7 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 	umh_info->pipe_to_umh = to_umh[1];
 	umh_info->pipe_from_umh = from_umh[0];
 	umh_info->pid = task_pid_nr(current);
+	current->flags |= PF_UMH;
 	return 0;
 }
 
-- 
2.25.0

[PATCH v3 03/16] umh: Rename the user mode driver helpers for clarity

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:47:44

Now that the functionality of umh_setup_pipe and
umh_clean_and_save_pid has changed their names are too specific and
don't make much sense.  Instead name them  umd_setup and umd_cleanup
for the functional role in setting up user mode drivers.

v1: https://lkml.kernel.org/r/875zbegf82.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87tuyt63x3.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 kernel/umh.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/umh.c b/kernel/umh.c
index e6b9d6636850..26c3d493f168 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -429,7 +429,7 @@ struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
 	return sub_info;
 }
 
-static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
+static int umd_setup(struct subprocess_info *info, struct cred *new)
 {
 	struct umh_info *umh_info = info->data;
 	struct file *from_umh[2];
@@ -470,11 +470,11 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 	return 0;
 }
 
-static void umh_clean_and_save_pid(struct subprocess_info *info)
+static void umd_cleanup(struct subprocess_info *info)
 {
 	struct umh_info *umh_info = info->data;
 
-	/* cleanup if umh_pipe_setup() was successful but exec failed */
+	/* cleanup if umh_setup() was successful but exec failed */
 	if (info->retval) {
 		fput(umh_info->pipe_to_umh);
 		fput(umh_info->pipe_from_umh);
@@ -520,8 +520,8 @@ int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 	}
 
 	err = -ENOMEM;
-	sub_info = call_usermodehelper_setup_file(file, umh_pipe_setup,
-						  umh_clean_and_save_pid, info);
+	sub_info = call_usermodehelper_setup_file(file, umd_setup, umd_cleanup,
+						  info);
 	if (!sub_info)
 		goto out;
 
-- 
2.25.0

[PATCH v3 04/16] umh: Remove call_usermodehelper_setup_file.

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:47:50

The only caller of call_usermodehelper_setup_file is fork_usermode_blob.
In fork_usermode_blob replace call_usermodehelper_setup_file with
call_usermodehelper_setup and delete fork_usermodehelper_setup_file.

For this to work the argv_free is moved from umh_clean_and_save_pid
to fork_usermode_blob.

v1: https://lkml.kernel.org/r/87zh8qf0mp.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87o8p163u1.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/umh.h |  3 ---
 kernel/umh.c        | 42 +++++++++++-------------------------------
 2 files changed, 11 insertions(+), 34 deletions(-)
diff --git a/include/linux/umh.h b/include/linux/umh.h
index aae16a0ebd0f..de08af00c68a 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -39,9 +39,6 @@ call_usermodehelper_setup(const char *path, char **argv, char **envp,
 			  int (*init)(struct subprocess_info *info, struct cred *new),
 			  void (*cleanup)(struct subprocess_info *), void *data);
 
-struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
-			  int (*init)(struct subprocess_info *info, struct cred *new),
-			  void (*cleanup)(struct subprocess_info *), void *data);
 struct umh_info {
 	const char *cmdline;
 	struct file *pipe_to_umh;
diff --git a/kernel/umh.c b/kernel/umh.c
index 26c3d493f168..b8fa9b99b366 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -402,33 +402,6 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
 }
 EXPORT_SYMBOL(call_usermodehelper_setup);
 
-struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
-		int (*init)(struct subprocess_info *info, struct cred *new),
-		void (*cleanup)(struct subprocess_info *info), void *data)
-{
-	struct subprocess_info *sub_info;
-	struct umh_info *info = data;
-	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
-
-	sub_info = kzalloc(sizeof(struct subprocess_info), GFP_KERNEL);
-	if (!sub_info)
-		return NULL;
-
-	sub_info->argv = argv_split(GFP_KERNEL, cmdline, NULL);
-	if (!sub_info->argv) {
-		kfree(sub_info);
-		return NULL;
-	}
-
-	INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
-	sub_info->path = "none";
-	sub_info->file = file;
-	sub_info->init = init;
-	sub_info->cleanup = cleanup;
-	sub_info->data = data;
-	return sub_info;
-}
-
 static int umd_setup(struct subprocess_info *info, struct cred *new)
 {
 	struct umh_info *umh_info = info->data;
@@ -479,8 +452,6 @@ static void umd_cleanup(struct subprocess_info *info)
 		fput(umh_info->pipe_to_umh);
 		fput(umh_info->pipe_from_umh);
 	}
-
-	argv_free(info->argv);
 }
 
 /**
@@ -501,7 +472,9 @@ static void umd_cleanup(struct subprocess_info *info)
  */
 int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 {
+	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
 	struct subprocess_info *sub_info;
+	char **argv = NULL;
 	struct file *file;
 	ssize_t written;
 	loff_t pos = 0;
@@ -520,11 +493,16 @@ int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 	}
 
 	err = -ENOMEM;
-	sub_info = call_usermodehelper_setup_file(file, umd_setup, umd_cleanup,
-						  info);
+	argv = argv_split(GFP_KERNEL, cmdline, NULL);
+	if (!argv)
+		goto out;
+
+	sub_info = call_usermodehelper_setup("none", argv, NULL, GFP_KERNEL,
+					     umd_setup, umd_cleanup, info);
 	if (!sub_info)
 		goto out;
 
+	sub_info->file = file;
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 	if (!err) {
 		mutex_lock(&umh_list_lock);
@@ -532,6 +510,8 @@ int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 		mutex_unlock(&umh_list_lock);
 	}
 out:
+	if (argv)
+		argv_free(argv);
 	fput(file);
 	return err;
 }
-- 
2.25.0

[PATCH v3 06/16] umd: For clarity rename umh_info umd_info

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:47:57

This structure is only used for user mode drivers so change
the prefix from umh to umd to make that clear.

v1: https://lkml.kernel.org/r/87o8p6f0kw.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/878sg563po.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/bpfilter.h        |  2 +-
 include/linux/usermode_driver.h |  6 +++---
 kernel/usermode_driver.c        | 20 ++++++++++----------
 net/ipv4/bpfilter/sockopt.c     |  2 +-
 4 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/include/linux/bpfilter.h b/include/linux/bpfilter.h
index d6d6206052a6..ec9972d822e0 100644
--- a/include/linux/bpfilter.h
+++ b/include/linux/bpfilter.h
@@ -11,7 +11,7 @@ int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
 int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
 			    int __user *optlen);
 struct bpfilter_umh_ops {
-	struct umh_info info;
+	struct umd_info info;
 	/* since ip_getsockopt() can run in parallel, serialize access to umh */
 	struct mutex lock;
 	int (*sockopt)(struct sock *sk, int optname,
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index c5f6dc950227..7131ea611bab 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -17,14 +17,14 @@ static inline void exit_umh(struct task_struct *tsk)
 }
 #endif
 
-struct umh_info {
+struct umd_info {
 	const char *cmdline;
 	struct file *pipe_to_umh;
 	struct file *pipe_from_umh;
 	struct list_head list;
-	void (*cleanup)(struct umh_info *info);
+	void (*cleanup)(struct umd_info *info);
 	pid_t pid;
 };
-int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
+int fork_usermode_blob(void *data, size_t len, struct umd_info *info);
 
 #endif /* __LINUX_USERMODE_DRIVER_H__ */
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index 5b05863af855..e73550e946d6 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -11,7 +11,7 @@ static DEFINE_MUTEX(umh_list_lock);
 
 static int umd_setup(struct subprocess_info *info, struct cred *new)
 {
-	struct umh_info *umh_info = info->data;
+	struct umd_info *umd_info = info->data;
 	struct file *from_umh[2];
 	struct file *to_umh[2];
 	int err;
@@ -43,21 +43,21 @@ static int umd_setup(struct subprocess_info *info, struct cred *new)
 		return err;
 	}
 
-	umh_info->pipe_to_umh = to_umh[1];
-	umh_info->pipe_from_umh = from_umh[0];
-	umh_info->pid = task_pid_nr(current);
+	umd_info->pipe_to_umh = to_umh[1];
+	umd_info->pipe_from_umh = from_umh[0];
+	umd_info->pid = task_pid_nr(current);
 	current->flags |= PF_UMH;
 	return 0;
 }
 
 static void umd_cleanup(struct subprocess_info *info)
 {
-	struct umh_info *umh_info = info->data;
+	struct umd_info *umd_info = info->data;
 
 	/* cleanup if umh_setup() was successful but exec failed */
 	if (info->retval) {
-		fput(umh_info->pipe_to_umh);
-		fput(umh_info->pipe_from_umh);
+		fput(umd_info->pipe_to_umh);
+		fput(umd_info->pipe_from_umh);
 	}
 }
 
@@ -72,12 +72,12 @@ static void umd_cleanup(struct subprocess_info *info)
  *
  * Returns either negative error or zero which indicates success
  * in executing a blob of bytes as a usermode process. In such
- * case 'struct umh_info *info' is populated with two pipes
+ * case 'struct umd_info *info' is populated with two pipes
  * and a pid of the process. The caller is responsible for health
  * check of the user process, killing it via pid, and closing the
  * pipes when user process is no longer needed.
  */
-int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
+int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 {
 	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
 	struct subprocess_info *sub_info;
@@ -126,7 +126,7 @@ EXPORT_SYMBOL_GPL(fork_usermode_blob);
 
 void __exit_umh(struct task_struct *tsk)
 {
-	struct umh_info *info;
+	struct umd_info *info;
 	pid_t pid = tsk->pid;
 
 	mutex_lock(&umh_list_lock);
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index 0480918bfc7c..c0dbcc86fcdb 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -12,7 +12,7 @@
 struct bpfilter_umh_ops bpfilter_ops;
 EXPORT_SYMBOL_GPL(bpfilter_ops);
 
-static void bpfilter_umh_cleanup(struct umh_info *info)
+static void bpfilter_umh_cleanup(struct umd_info *info)
 {
 	mutex_lock(&bpfilter_ops.lock);
 	bpfilter_ops.stop = true;
-- 
2.25.0

[PATCH v3 08/16] umd: Transform fork_usermode_blob into fork_usermode_driver

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:05

Instead of loading a binary blob into a temporary file with
shmem_kernel_file_setup load a binary blob into a temporary tmpfs
filesystem.  This means that the blob can be stored in an init section
and discared, and it means the binary blob will have a filename so can
be executed normally.

The only tricky thing about this code is that in the helper function
blob_to_mnt __fput_sync is used.  That is because a file can not be
executed if it is still open for write, and the ordinary delayed close
for kernel threads does not happen soon enough, which causes the
following exec to fail.  The function umd_load_blob is not called with
any locks so this should be safe.

Executing the blob normally winds up correcting several problems with
the user mode driver code discovered by Tetsuo Handa[1].  By passing
an ordinary filename into the exec, it is no longer necessary to
figure out how to turn a O_RDWR file descriptor into a properly
referende counted O_EXEC file descriptor that forbids all writes.  For
path based LSMs there are no new special cases.

[1] https://lore.kernel.org/linux-fsdevel/2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp/
v1: https://lkml.kernel.org/r/87d05mf0j9.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87wo3p4p35.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/usermode_driver.h |   6 +-
 kernel/usermode_driver.c        | 126 ++++++++++++++++++++++++--------
 net/bpfilter/bpfilter_kern.c    |  14 +++-
 3 files changed, 113 insertions(+), 33 deletions(-)
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 48cf25e3145d..97c919b7147c 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -2,6 +2,7 @@
 #define __LINUX_USERMODE_DRIVER_H__
 
 #include <linux/umh.h>
+#include <linux/path.h>
 
 #ifdef CONFIG_BPFILTER
 void __exit_umh(struct task_struct *tsk);
@@ -23,8 +24,11 @@ struct umd_info {
 	struct file *pipe_from_umh;
 	struct list_head list;
 	void (*cleanup)(struct umd_info *info);
+	struct path wd;
 	pid_t pid;
 };
-int fork_usermode_blob(void *data, size_t len, struct umd_info *info);
+int umd_load_blob(struct umd_info *info, const void *data, size_t len);
+int umd_unload_blob(struct umd_info *info);
+int fork_usermode_driver(struct umd_info *info);
 
 #endif /* __LINUX_USERMODE_DRIVER_H__ */
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index 46d60d855e93..a86798759f83 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -4,11 +4,98 @@
  */
 #include <linux/shmem_fs.h>
 #include <linux/pipe_fs_i.h>
+#include <linux/mount.h>
+#include <linux/fs_struct.h>
+#include <linux/task_work.h>
 #include <linux/usermode_driver.h>
 
 static LIST_HEAD(umh_list);
 static DEFINE_MUTEX(umh_list_lock);
 
+static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
+{
+	struct file_system_type *type;
+	struct vfsmount *mnt;
+	struct file *file;
+	ssize_t written;
+	loff_t pos = 0;
+
+	type = get_fs_type("tmpfs");
+	if (!type)
+		return ERR_PTR(-ENODEV);
+
+	mnt = kern_mount(type);
+	put_filesystem(type);
+	if (IS_ERR(mnt))
+		return mnt;
+
+	file = file_open_root(mnt->mnt_root, mnt, name, O_CREAT | O_WRONLY, 0700);
+	if (IS_ERR(file)) {
+		mntput(mnt);
+		return ERR_CAST(file);
+	}
+
+	written = kernel_write(file, data, len, &pos);
+	if (written != len) {
+		int err = written;
+		if (err >= 0)
+			err = -ENOMEM;
+		filp_close(file, NULL);
+		mntput(mnt);
+		return ERR_PTR(err);
+	}
+
+	fput(file);
+
+	/* Flush delayed fput so exec can open the file read-only */
+	flush_delayed_fput();
+	task_work_run();
+	return mnt;
+}
+
+/**
+ * umd_load_blob - Remember a blob of bytes for fork_usermode_driver
+ * @info: information about usermode driver
+ * @data: a blob of bytes that can be executed as a file
+ * @len:  The lentgh of the blob
+ *
+ */
+int umd_load_blob(struct umd_info *info, const void *data, size_t len)
+{
+	struct vfsmount *mnt;
+
+	if (WARN_ON_ONCE(info->wd.dentry || info->wd.mnt))
+		return -EBUSY;
+
+	mnt = blob_to_mnt(data, len, info->driver_name);
+	if (IS_ERR(mnt))
+		return PTR_ERR(mnt);
+
+	info->wd.mnt = mnt;
+	info->wd.dentry = mnt->mnt_root;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(umd_load_blob);
+
+/**
+ * umd_unload_blob - Disassociate @info from a previously loaded blob
+ * @info: information about usermode driver
+ *
+ */
+int umd_unload_blob(struct umd_info *info)
+{
+	if (WARN_ON_ONCE(!info->wd.mnt ||
+			 !info->wd.dentry ||
+			 info->wd.mnt->mnt_root != info->wd.dentry))
+		return -EINVAL;
+
+	kern_unmount(info->wd.mnt);
+	info->wd.mnt = NULL;
+	info->wd.dentry = NULL;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(umd_unload_blob);
+
 static int umd_setup(struct subprocess_info *info, struct cred *new)
 {
 	struct umd_info *umd_info = info->data;
@@ -43,6 +130,7 @@ static int umd_setup(struct subprocess_info *info, struct cred *new)
 		return err;
 	}
 
+	set_fs_pwd(current->fs, &umd_info->wd);
 	umd_info->pipe_to_umh = to_umh[1];
 	umd_info->pipe_from_umh = from_umh[0];
 	umd_info->pid = task_pid_nr(current);
@@ -62,39 +150,21 @@ static void umd_cleanup(struct subprocess_info *info)
 }
 
 /**
- * fork_usermode_blob - fork a blob of bytes as a usermode process
- * @data: a blob of bytes that can be do_execv-ed as a file
- * @len: length of the blob
- * @info: information about usermode process (shouldn't be NULL)
+ * fork_usermode_driver - fork a usermode driver
+ * @info: information about usermode driver (shouldn't be NULL)
  *
- * Returns either negative error or zero which indicates success
- * in executing a blob of bytes as a usermode process. In such
- * case 'struct umd_info *info' is populated with two pipes
- * and a pid of the process. The caller is responsible for health
- * check of the user process, killing it via pid, and closing the
- * pipes when user process is no longer needed.
+ * Returns either negative error or zero which indicates success in
+ * executing a usermode driver. In such case 'struct umd_info *info'
+ * is populated with two pipes and a pid of the process. The caller is
+ * responsible for health check of the user process, killing it via
+ * pid, and closing the pipes when user process is no longer needed.
  */
-int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
+int fork_usermode_driver(struct umd_info *info)
 {
 	struct subprocess_info *sub_info;
 	char **argv = NULL;
-	struct file *file;
-	ssize_t written;
-	loff_t pos = 0;
 	int err;
 
-	file = shmem_kernel_file_setup(info->driver_name, len, 0);
-	if (IS_ERR(file))
-		return PTR_ERR(file);
-
-	written = kernel_write(file, data, len, &pos);
-	if (written != len) {
-		err = written;
-		if (err >= 0)
-			err = -ENOMEM;
-		goto out;
-	}
-
 	err = -ENOMEM;
 	argv = argv_split(GFP_KERNEL, info->driver_name, NULL);
 	if (!argv)
@@ -106,7 +176,6 @@ int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 	if (!sub_info)
 		goto out;
 
-	sub_info->file = file;
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 	if (!err) {
 		mutex_lock(&umh_list_lock);
@@ -116,10 +185,9 @@ int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 out:
 	if (argv)
 		argv_free(argv);
-	fput(file);
 	return err;
 }
-EXPORT_SYMBOL_GPL(fork_usermode_blob);
+EXPORT_SYMBOL_GPL(fork_usermode_driver);
 
 void __exit_umh(struct task_struct *tsk)
 {
diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index c0f0990f30b6..28883b00609d 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -77,9 +77,7 @@ static int start_umh(void)
 	int err;
 
 	/* fork usermode process */
-	err = fork_usermode_blob(&bpfilter_umh_start,
-				 &bpfilter_umh_end - &bpfilter_umh_start,
-				 &bpfilter_ops.info);
+	err = fork_usermode_driver(&bpfilter_ops.info);
 	if (err)
 		return err;
 	bpfilter_ops.stop = false;
@@ -98,6 +96,12 @@ static int __init load_umh(void)
 {
 	int err;
 
+	err = umd_load_blob(&bpfilter_ops.info,
+			    &bpfilter_umh_start,
+			    &bpfilter_umh_end - &bpfilter_umh_start);
+	if (err)
+		return err;
+
 	mutex_lock(&bpfilter_ops.lock);
 	if (!bpfilter_ops.stop) {
 		err = -EFAULT;
@@ -110,6 +114,8 @@ static int __init load_umh(void)
 	}
 out:
 	mutex_unlock(&bpfilter_ops.lock);
+	if (err)
+		umd_unload_blob(&bpfilter_ops.info);
 	return err;
 }
 
@@ -122,6 +128,8 @@ static void __exit fini_umh(void)
 		bpfilter_ops.sockopt = NULL;
 	}
 	mutex_unlock(&bpfilter_ops.lock);
+
+	umd_unload_blob(&bpfilter_ops.info);
 }
 module_init(load_umh);
 module_exit(fini_umh);
-- 
2.25.0

[PATCH v3 07/16] umd: Rename umd_info.cmdline umd_info.driver_name

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:08

The only thing supplied in the cmdline today is the driver name so
rename the field to clarify the code.

As this value is always supplied stop trying to handle the case of
a NULL cmdline.

Additionally since we now have a name we can count on use the
driver_name any place where the code is looking for a name
of the binary.

v1: https://lkml.kernel.org/r/87imfef0k3.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87366d63os.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/usermode_driver.h |  2 +-
 kernel/usermode_driver.c        | 11 ++++-------
 net/ipv4/bpfilter/sockopt.c     |  2 +-
 3 files changed, 6 insertions(+), 9 deletions(-)
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 7131ea611bab..48cf25e3145d 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -18,7 +18,7 @@ static inline void exit_umh(struct task_struct *tsk)
 #endif
 
 struct umd_info {
-	const char *cmdline;
+	const char *driver_name;
 	struct file *pipe_to_umh;
 	struct file *pipe_from_umh;
 	struct list_head list;
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index e73550e946d6..46d60d855e93 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -67,9 +67,6 @@ static void umd_cleanup(struct subprocess_info *info)
  * @len: length of the blob
  * @info: information about usermode process (shouldn't be NULL)
  *
- * If info->cmdline is set it will be used as command line for the
- * user process, else "usermodehelper" is used.
- *
  * Returns either negative error or zero which indicates success
  * in executing a blob of bytes as a usermode process. In such
  * case 'struct umd_info *info' is populated with two pipes
@@ -79,7 +76,6 @@ static void umd_cleanup(struct subprocess_info *info)
  */
 int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 {
-	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
 	struct subprocess_info *sub_info;
 	char **argv = NULL;
 	struct file *file;
@@ -87,7 +83,7 @@ int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 	loff_t pos = 0;
 	int err;
 
-	file = shmem_kernel_file_setup("", len, 0);
+	file = shmem_kernel_file_setup(info->driver_name, len, 0);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
@@ -100,11 +96,12 @@ int fork_usermode_blob(void *data, size_t len, struct umd_info *info)
 	}
 
 	err = -ENOMEM;
-	argv = argv_split(GFP_KERNEL, cmdline, NULL);
+	argv = argv_split(GFP_KERNEL, info->driver_name, NULL);
 	if (!argv)
 		goto out;
 
-	sub_info = call_usermodehelper_setup("none", argv, NULL, GFP_KERNEL,
+	sub_info = call_usermodehelper_setup(info->driver_name, argv, NULL,
+					     GFP_KERNEL,
 					     umd_setup, umd_cleanup, info);
 	if (!sub_info)
 		goto out;
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index c0dbcc86fcdb..5050de28333d 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -70,7 +70,7 @@ static int __init bpfilter_sockopt_init(void)
 {
 	mutex_init(&bpfilter_ops.lock);
 	bpfilter_ops.stop = true;
-	bpfilter_ops.info.cmdline = "bpfilter_umh";
+	bpfilter_ops.info.driver_name = "bpfilter_umh";
 	bpfilter_ops.info.cleanup = &bpfilter_umh_cleanup;
 
 	return 0;
-- 
2.25.0

[PATCH v3 09/16] umh: Stop calling do_execve_file

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:15

With the user mode driver code changed to not set subprocess_info.file
there are no more users of subproces_info.file.  Remove this field
from struct subprocess_info and remove the only user in
call_usermodehelper_exec_async that would call do_execve_file instead
of do_execve if file was set.

v1: https://lkml.kernel.org/r/877dvuf0i7.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87r1tx4p2a.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/umh.h |  1 -
 kernel/umh.c        | 10 +++-------
 2 files changed, 3 insertions(+), 8 deletions(-)
diff --git a/include/linux/umh.h b/include/linux/umh.h
index 73173c4a07e5..244aff638220 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -22,7 +22,6 @@ struct subprocess_info {
 	const char *path;
 	char **argv;
 	char **envp;
-	struct file *file;
 	int wait;
 	int retval;
 	int (*init)(struct subprocess_info *info, struct cred *new);
diff --git a/kernel/umh.c b/kernel/umh.c
index 3e4e453d45c8..6ca2096298b9 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -98,13 +98,9 @@ static int call_usermodehelper_exec_async(void *data)
 
 	commit_creds(new);
 
-	if (sub_info->file)
-		retval = do_execve_file(sub_info->file,
-					sub_info->argv, sub_info->envp);
-	else
-		retval = do_execve(getname_kernel(sub_info->path),
-				   (const char __user *const __user *)sub_info->argv,
-				   (const char __user *const __user *)sub_info->envp);
+	retval = do_execve(getname_kernel(sub_info->path),
+			   (const char __user *const __user *)sub_info->argv,
+			   (const char __user *const __user *)sub_info->envp);
 out:
 	sub_info->retval = retval;
 	/*
-- 
2.25.0

[PATCH v3 10/16] exec: Remove do_execve_file

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:20

Now that the last callser has been removed remove this code from exec.

For anyone thinking of resurrecing do_execve_file please note that
the code was buggy in several fundamental ways.

- It did not ensure the file it was passed was read-only and that
  deny_write_access had been called on it.  Which subtlely breaks
  invaniants in exec.

- The caller of do_execve_file was expected to hold and put a
  reference to the file, but an extra reference for use by exec was
  not taken so that when exec put it's reference to the file an
  underflow occured on the file reference count.

- The point of the interface was so that a pathname did not need to
  exist.  Which breaks pathname based LSMs.

Tetsuo Handa originally reported these issues[1].  While it was clear
that deny_write_access was missing the fundamental incompatibility
with the passed in O_RDWR filehandle was not immediately recognized.

All of these issues were fixed by modifying the usermode driver code
to have a path, so it did not need this hack.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
[1] https://lore.kernel.org/linux-fsdevel/2a8775b4-1dd5-9d5c-aa42-9872445e0942@i-love.sakura.ne.jp/
v1: https://lkml.kernel.org/r/871rm2f0hi.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87lfk54p0m.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 fs/exec.c               | 38 +++++++++-----------------------------
 include/linux/binfmts.h |  1 -
 2 files changed, 9 insertions(+), 30 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index e6e8a9a70327..23dfbb820626 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1818,13 +1818,14 @@ static int exec_binprm(struct linux_binprm *bprm)
 /*
  * sys_execve() executes a new program.
  */
-static int __do_execve_file(int fd, struct filename *filename,
-			    struct user_arg_ptr argv,
-			    struct user_arg_ptr envp,
-			    int flags, struct file *file)
+static int do_execveat_common(int fd, struct filename *filename,
+			      struct user_arg_ptr argv,
+			      struct user_arg_ptr envp,
+			      int flags)
 {
 	char *pathbuf = NULL;
 	struct linux_binprm *bprm;
+	struct file *file;
 	struct files_struct *displaced;
 	int retval;
 
@@ -1863,8 +1864,7 @@ static int __do_execve_file(int fd, struct filename *filename,
 	check_unsafe_exec(bprm);
 	current->in_execve = 1;
 
-	if (!file)
-		file = do_open_execat(fd, filename, flags);
+	file = do_open_execat(fd, filename, flags);
 	retval = PTR_ERR(file);
 	if (IS_ERR(file))
 		goto out_unmark;
@@ -1872,9 +1872,7 @@ static int __do_execve_file(int fd, struct filename *filename,
 	sched_exec();
 
 	bprm->file = file;
-	if (!filename) {
-		bprm->filename = "none";
-	} else if (fd == AT_FDCWD || filename->name[0] == '/') {
+	if (fd == AT_FDCWD || filename->name[0] == '/') {
 		bprm->filename = filename->name;
 	} else {
 		if (filename->name[0] == '\0')
@@ -1935,8 +1933,7 @@ static int __do_execve_file(int fd, struct filename *filename,
 	task_numa_free(current, false);
 	free_bprm(bprm);
 	kfree(pathbuf);
-	if (filename)
-		putname(filename);
+	putname(filename);
 	if (displaced)
 		put_files_struct(displaced);
 	return retval;
@@ -1967,27 +1964,10 @@ static int __do_execve_file(int fd, struct filename *filename,
 	if (displaced)
 		reset_files_struct(displaced);
 out_ret:
-	if (filename)
-		putname(filename);
+	putname(filename);
 	return retval;
 }
 
-static int do_execveat_common(int fd, struct filename *filename,
-			      struct user_arg_ptr argv,
-			      struct user_arg_ptr envp,
-			      int flags)
-{
-	return __do_execve_file(fd, filename, argv, envp, flags, NULL);
-}
-
-int do_execve_file(struct file *file, void *__argv, void *__envp)
-{
-	struct user_arg_ptr argv = { .ptr.native = __argv };
-	struct user_arg_ptr envp = { .ptr.native = __envp };
-
-	return __do_execve_file(AT_FDCWD, NULL, argv, envp, 0, file);
-}
-
 int do_execve(struct filename *filename,
 	const char __user *const __user *__argv,
 	const char __user *const __user *__envp)
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 4a20b7517dd0..7c27d7b57871 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -141,6 +141,5 @@ extern int do_execveat(int, struct filename *,
 		       const char __user * const __user *,
 		       const char __user * const __user *,
 		       int);
-int do_execve_file(struct file *file, void *__argv, void *__envp);
 
 #endif /* _LINUX_BINFMTS_H */
-- 
2.25.0

[PATCH v3 05/16] umh: Separate the user mode driver and the user mode helper support

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:21

This makes it clear which code is part of the core user mode
helper support and which code is needed to implement user mode
drivers.

This makes the kernel smaller for everyone who does not use a usermode
driver.

v1: https://lkml.kernel.org/r/87tuyyf0ln.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87imf963s6.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/bpfilter.h        |   2 +-
 include/linux/sched.h           |   8 --
 include/linux/umh.h             |  10 ---
 include/linux/usermode_driver.h |  30 +++++++
 kernel/Makefile                 |   1 +
 kernel/exit.c                   |   1 +
 kernel/umh.c                    | 139 ------------------------------
 kernel/usermode_driver.c        | 146 ++++++++++++++++++++++++++++++++
 8 files changed, 179 insertions(+), 158 deletions(-)
 create mode 100644 include/linux/usermode_driver.h
 create mode 100644 kernel/usermode_driver.c
diff --git a/include/linux/bpfilter.h b/include/linux/bpfilter.h
index d815622cd31e..d6d6206052a6 100644
--- a/include/linux/bpfilter.h
+++ b/include/linux/bpfilter.h
@@ -3,7 +3,7 @@
 #define _LINUX_BPFILTER_H
 
 #include <uapi/linux/bpfilter.h>
-#include <linux/umh.h>
+#include <linux/usermode_driver.h>
 
 struct sock;
 int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b62e6aaf28f0..59d1e92bb88e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2020,14 +2020,6 @@ static inline void rseq_execve(struct task_struct *t)
 
 #endif
 
-void __exit_umh(struct task_struct *tsk);
-
-static inline void exit_umh(struct task_struct *tsk)
-{
-	if (unlikely(tsk->flags & PF_UMH))
-		__exit_umh(tsk);
-}
-
 #ifdef CONFIG_DEBUG_RSEQ
 
 void rseq_syscall(struct pt_regs *regs);
diff --git a/include/linux/umh.h b/include/linux/umh.h
index de08af00c68a..73173c4a07e5 100644
--- a/include/linux/umh.h
+++ b/include/linux/umh.h
@@ -39,16 +39,6 @@ call_usermodehelper_setup(const char *path, char **argv, char **envp,
 			  int (*init)(struct subprocess_info *info, struct cred *new),
 			  void (*cleanup)(struct subprocess_info *), void *data);
 
-struct umh_info {
-	const char *cmdline;
-	struct file *pipe_to_umh;
-	struct file *pipe_from_umh;
-	struct list_head list;
-	void (*cleanup)(struct umh_info *info);
-	pid_t pid;
-};
-int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
-
 extern int
 call_usermodehelper_exec(struct subprocess_info *info, int wait);
 
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
new file mode 100644
index 000000000000..c5f6dc950227
--- /dev/null
+++ b/include/linux/usermode_driver.h
@@ -0,0 +1,30 @@
+#ifndef __LINUX_USERMODE_DRIVER_H__
+#define __LINUX_USERMODE_DRIVER_H__
+
+#include <linux/umh.h>
+
+#ifdef CONFIG_BPFILTER
+void __exit_umh(struct task_struct *tsk);
+
+static inline void exit_umh(struct task_struct *tsk)
+{
+	if (unlikely(tsk->flags & PF_UMH))
+		__exit_umh(tsk);
+}
+#else
+static inline void exit_umh(struct task_struct *tsk)
+{
+}
+#endif
+
+struct umh_info {
+	const char *cmdline;
+	struct file *pipe_to_umh;
+	struct file *pipe_from_umh;
+	struct list_head list;
+	void (*cleanup)(struct umh_info *info);
+	pid_t pid;
+};
+int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
+
+#endif /* __LINUX_USERMODE_DRIVER_H__ */
diff --git a/kernel/Makefile b/kernel/Makefile
index f3218bc5ec69..43928759893a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -12,6 +12,7 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
 	    async.o range.o smpboot.o ucount.o
 
+obj-$(CONFIG_BPFILTER) += usermode_driver.o
 obj-$(CONFIG_MODULES) += kmod.o
 obj-$(CONFIG_MULTIUSER) += groups.o
 
diff --git a/kernel/exit.c b/kernel/exit.c
index 727150f28103..a081deea52ca 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -63,6 +63,7 @@
 #include <linux/random.h>
 #include <linux/rcuwait.h>
 #include <linux/compat.h>
+#include <linux/usermode_driver.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
diff --git a/kernel/umh.c b/kernel/umh.c
index b8fa9b99b366..3e4e453d45c8 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -26,8 +26,6 @@
 #include <linux/ptrace.h>
 #include <linux/async.h>
 #include <linux/uaccess.h>
-#include <linux/shmem_fs.h>
-#include <linux/pipe_fs_i.h>
 
 #include <trace/events/module.h>
 
@@ -38,8 +36,6 @@ static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
 static DEFINE_SPINLOCK(umh_sysctl_lock);
 static DECLARE_RWSEM(umhelper_sem);
-static LIST_HEAD(umh_list);
-static DEFINE_MUTEX(umh_list_lock);
 
 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
@@ -402,121 +398,6 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
 }
 EXPORT_SYMBOL(call_usermodehelper_setup);
 
-static int umd_setup(struct subprocess_info *info, struct cred *new)
-{
-	struct umh_info *umh_info = info->data;
-	struct file *from_umh[2];
-	struct file *to_umh[2];
-	int err;
-
-	/* create pipe to send data to umh */
-	err = create_pipe_files(to_umh, 0);
-	if (err)
-		return err;
-	err = replace_fd(0, to_umh[0], 0);
-	fput(to_umh[0]);
-	if (err < 0) {
-		fput(to_umh[1]);
-		return err;
-	}
-
-	/* create pipe to receive data from umh */
-	err = create_pipe_files(from_umh, 0);
-	if (err) {
-		fput(to_umh[1]);
-		replace_fd(0, NULL, 0);
-		return err;
-	}
-	err = replace_fd(1, from_umh[1], 0);
-	fput(from_umh[1]);
-	if (err < 0) {
-		fput(to_umh[1]);
-		replace_fd(0, NULL, 0);
-		fput(from_umh[0]);
-		return err;
-	}
-
-	umh_info->pipe_to_umh = to_umh[1];
-	umh_info->pipe_from_umh = from_umh[0];
-	umh_info->pid = task_pid_nr(current);
-	current->flags |= PF_UMH;
-	return 0;
-}
-
-static void umd_cleanup(struct subprocess_info *info)
-{
-	struct umh_info *umh_info = info->data;
-
-	/* cleanup if umh_setup() was successful but exec failed */
-	if (info->retval) {
-		fput(umh_info->pipe_to_umh);
-		fput(umh_info->pipe_from_umh);
-	}
-}
-
-/**
- * fork_usermode_blob - fork a blob of bytes as a usermode process
- * @data: a blob of bytes that can be do_execv-ed as a file
- * @len: length of the blob
- * @info: information about usermode process (shouldn't be NULL)
- *
- * If info->cmdline is set it will be used as command line for the
- * user process, else "usermodehelper" is used.
- *
- * Returns either negative error or zero which indicates success
- * in executing a blob of bytes as a usermode process. In such
- * case 'struct umh_info *info' is populated with two pipes
- * and a pid of the process. The caller is responsible for health
- * check of the user process, killing it via pid, and closing the
- * pipes when user process is no longer needed.
- */
-int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
-{
-	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
-	struct subprocess_info *sub_info;
-	char **argv = NULL;
-	struct file *file;
-	ssize_t written;
-	loff_t pos = 0;
-	int err;
-
-	file = shmem_kernel_file_setup("", len, 0);
-	if (IS_ERR(file))
-		return PTR_ERR(file);
-
-	written = kernel_write(file, data, len, &pos);
-	if (written != len) {
-		err = written;
-		if (err >= 0)
-			err = -ENOMEM;
-		goto out;
-	}
-
-	err = -ENOMEM;
-	argv = argv_split(GFP_KERNEL, cmdline, NULL);
-	if (!argv)
-		goto out;
-
-	sub_info = call_usermodehelper_setup("none", argv, NULL, GFP_KERNEL,
-					     umd_setup, umd_cleanup, info);
-	if (!sub_info)
-		goto out;
-
-	sub_info->file = file;
-	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
-	if (!err) {
-		mutex_lock(&umh_list_lock);
-		list_add(&info->list, &umh_list);
-		mutex_unlock(&umh_list_lock);
-	}
-out:
-	if (argv)
-		argv_free(argv);
-	fput(file);
-	return err;
-}
-EXPORT_SYMBOL_GPL(fork_usermode_blob);
-
 /**
  * call_usermodehelper_exec - start a usermode application
  * @sub_info: information about the subprocessa
@@ -678,26 +559,6 @@ static int proc_cap_handler(struct ctl_table *table, int write,
 	return 0;
 }
 
-void __exit_umh(struct task_struct *tsk)
-{
-	struct umh_info *info;
-	pid_t pid = tsk->pid;
-
-	mutex_lock(&umh_list_lock);
-	list_for_each_entry(info, &umh_list, list) {
-		if (info->pid == pid) {
-			list_del(&info->list);
-			mutex_unlock(&umh_list_lock);
-			goto out;
-		}
-	}
-	mutex_unlock(&umh_list_lock);
-	return;
-out:
-	if (info->cleanup)
-		info->cleanup(info);
-}
-
 struct ctl_table usermodehelper_table[] = {
 	{
 		.procname	= "bset",
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
new file mode 100644
index 000000000000..5b05863af855
--- /dev/null
+++ b/kernel/usermode_driver.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * umd - User mode driver support
+ */
+#include <linux/shmem_fs.h>
+#include <linux/pipe_fs_i.h>
+#include <linux/usermode_driver.h>
+
+static LIST_HEAD(umh_list);
+static DEFINE_MUTEX(umh_list_lock);
+
+static int umd_setup(struct subprocess_info *info, struct cred *new)
+{
+	struct umh_info *umh_info = info->data;
+	struct file *from_umh[2];
+	struct file *to_umh[2];
+	int err;
+
+	/* create pipe to send data to umh */
+	err = create_pipe_files(to_umh, 0);
+	if (err)
+		return err;
+	err = replace_fd(0, to_umh[0], 0);
+	fput(to_umh[0]);
+	if (err < 0) {
+		fput(to_umh[1]);
+		return err;
+	}
+
+	/* create pipe to receive data from umh */
+	err = create_pipe_files(from_umh, 0);
+	if (err) {
+		fput(to_umh[1]);
+		replace_fd(0, NULL, 0);
+		return err;
+	}
+	err = replace_fd(1, from_umh[1], 0);
+	fput(from_umh[1]);
+	if (err < 0) {
+		fput(to_umh[1]);
+		replace_fd(0, NULL, 0);
+		fput(from_umh[0]);
+		return err;
+	}
+
+	umh_info->pipe_to_umh = to_umh[1];
+	umh_info->pipe_from_umh = from_umh[0];
+	umh_info->pid = task_pid_nr(current);
+	current->flags |= PF_UMH;
+	return 0;
+}
+
+static void umd_cleanup(struct subprocess_info *info)
+{
+	struct umh_info *umh_info = info->data;
+
+	/* cleanup if umh_setup() was successful but exec failed */
+	if (info->retval) {
+		fput(umh_info->pipe_to_umh);
+		fput(umh_info->pipe_from_umh);
+	}
+}
+
+/**
+ * fork_usermode_blob - fork a blob of bytes as a usermode process
+ * @data: a blob of bytes that can be do_execv-ed as a file
+ * @len: length of the blob
+ * @info: information about usermode process (shouldn't be NULL)
+ *
+ * If info->cmdline is set it will be used as command line for the
+ * user process, else "usermodehelper" is used.
+ *
+ * Returns either negative error or zero which indicates success
+ * in executing a blob of bytes as a usermode process. In such
+ * case 'struct umh_info *info' is populated with two pipes
+ * and a pid of the process. The caller is responsible for health
+ * check of the user process, killing it via pid, and closing the
+ * pipes when user process is no longer needed.
+ */
+int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
+{
+	const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
+	struct subprocess_info *sub_info;
+	char **argv = NULL;
+	struct file *file;
+	ssize_t written;
+	loff_t pos = 0;
+	int err;
+
+	file = shmem_kernel_file_setup("", len, 0);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	written = kernel_write(file, data, len, &pos);
+	if (written != len) {
+		err = written;
+		if (err >= 0)
+			err = -ENOMEM;
+		goto out;
+	}
+
+	err = -ENOMEM;
+	argv = argv_split(GFP_KERNEL, cmdline, NULL);
+	if (!argv)
+		goto out;
+
+	sub_info = call_usermodehelper_setup("none", argv, NULL, GFP_KERNEL,
+					     umd_setup, umd_cleanup, info);
+	if (!sub_info)
+		goto out;
+
+	sub_info->file = file;
+	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
+	if (!err) {
+		mutex_lock(&umh_list_lock);
+		list_add(&info->list, &umh_list);
+		mutex_unlock(&umh_list_lock);
+	}
+out:
+	if (argv)
+		argv_free(argv);
+	fput(file);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fork_usermode_blob);
+
+void __exit_umh(struct task_struct *tsk)
+{
+	struct umh_info *info;
+	pid_t pid = tsk->pid;
+
+	mutex_lock(&umh_list_lock);
+	list_for_each_entry(info, &umh_list, list) {
+		if (info->pid == pid) {
+			list_del(&info->list);
+			mutex_unlock(&umh_list_lock);
+			goto out;
+		}
+	}
+	mutex_unlock(&umh_list_lock);
+	return;
+out:
+	if (info->cleanup)
+		info->cleanup(info);
+}
+
-- 
2.25.0

[PATCH v3 13/16] exit: Factor thread_group_exited out of pidfd_poll

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:42

Create an independent helper thread_group_exited report return true
when all threads have passed exit_notify in do_exit.  AKA all of the
threads are at least zombies and might be dead or completely gone.

Create this helper by taking the logic out of pidfd_poll where
it is already tested, and adding a missing READ_ONCE on
the read of task->exit_state.

I will be changing the user mode driver code to use this same logic
to know when a user mode driver needs to be restarted.

Place the new helper thread_group_exited in kernel/exit.c and
EXPORT it so it can be used by modules.

Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/sched/signal.h |  2 ++
 kernel/exit.c                | 24 ++++++++++++++++++++++++
 kernel/fork.c                |  6 +-----
 3 files changed, 27 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 0ee5e696c5d8..1bad18a1d8ba 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -674,6 +674,8 @@ static inline int thread_group_empty(struct task_struct *p)
 #define delay_group_leader(p) \
 		(thread_group_leader(p) && !thread_group_empty(p))
 
+extern bool thread_group_exited(struct pid *pid);
+
 extern struct sighand_struct *__lock_task_sighand(struct task_struct *task,
 							unsigned long *flags);
 
diff --git a/kernel/exit.c b/kernel/exit.c
index d3294b611df1..a7f112feb0f6 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1713,6 +1713,30 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 }
 #endif
 
+/**
+ * thread_group_exited - check that a thread group has exited
+ * @pid: tgid of thread group to be checked.
+ *
+ * Test if thread group is has exited (all threads are zombies, dead
+ * or completely gone).
+ *
+ * Return: true if the thread group has exited. false otherwise.
+ */
+bool thread_group_exited(struct pid *pid)
+{
+	struct task_struct *task;
+	bool exited;
+
+	rcu_read_lock();
+	task = pid_task(pid, PIDTYPE_PID);
+	exited = !task ||
+		(READ_ONCE(task->exit_state) && thread_group_empty(task));
+	rcu_read_unlock();
+
+	return exited;
+}
+EXPORT_SYMBOL(thread_group_exited);
+
 __weak void abort(void)
 {
 	BUG();
diff --git a/kernel/fork.c b/kernel/fork.c
index 142b23645d82..bf215af7a904 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1787,22 +1787,18 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
  */
 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 {
-	struct task_struct *task;
 	struct pid *pid = file->private_data;
 	__poll_t poll_flags = 0;
 
 	poll_wait(file, &pid->wait_pidfd, pts);
 
-	rcu_read_lock();
-	task = pid_task(pid, PIDTYPE_PID);
 	/*
 	 * Inform pollers only when the whole thread group exits.
 	 * If the thread group leader exits before all other threads in the
 	 * group, then poll(2) should block, similar to the wait(2) family.
 	 */
-	if (!task || (task->exit_state && thread_group_empty(task)))
+	if (thread_group_exited(pid))
 		poll_flags = EPOLLIN | EPOLLRDNORM;
-	rcu_read_unlock();
 
 	return poll_flags;
 }
-- 
2.25.0

[PATCH v3 15/16] umd: Remove exit_umh

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:56

The bpfilter code no longer uses the umd_info.cleanup callback.  This
callback is what exit_umh exists to call.  So remove exit_umh and all
of it's associated booking.

v1: https://lkml.kernel.org/r/87bll6dlte.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87y2o53abg.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/sched.h           |  1 -
 include/linux/usermode_driver.h | 16 ----------------
 kernel/exit.c                   |  3 ---
 kernel/usermode_driver.c        | 28 ----------------------------
 4 files changed, 48 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 59d1e92bb88e..edb2020875ad 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1511,7 +1511,6 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
-#define PF_UMH			0x02000000	/* I'm an Usermodehelper process */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_NOCMA	0x10000000	/* All allocation request will have _GFP_MOVABLE cleared */
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 45adbffb31d9..073a9e0ec07d 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -4,26 +4,10 @@
 #include <linux/umh.h>
 #include <linux/path.h>
 
-#ifdef CONFIG_BPFILTER
-void __exit_umh(struct task_struct *tsk);
-
-static inline void exit_umh(struct task_struct *tsk)
-{
-	if (unlikely(tsk->flags & PF_UMH))
-		__exit_umh(tsk);
-}
-#else
-static inline void exit_umh(struct task_struct *tsk)
-{
-}
-#endif
-
 struct umd_info {
 	const char *driver_name;
 	struct file *pipe_to_umh;
 	struct file *pipe_from_umh;
-	struct list_head list;
-	void (*cleanup)(struct umd_info *info);
 	struct path wd;
 	struct pid *tgid;
 };
diff --git a/kernel/exit.c b/kernel/exit.c
index a7f112feb0f6..4ec82859bfe5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -63,7 +63,6 @@
 #include <linux/random.h>
 #include <linux/rcuwait.h>
 #include <linux/compat.h>
-#include <linux/usermode_driver.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -805,8 +804,6 @@ void __noreturn do_exit(long code)
 	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
 	exit_thread(tsk);
-	if (group_dead)
-		exit_umh(tsk);
 
 	/*
 	 * Flush inherited counters to the parent - before the parent
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index f77f8d7ce9e3..cd136f86f799 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -9,9 +9,6 @@
 #include <linux/task_work.h>
 #include <linux/usermode_driver.h>
 
-static LIST_HEAD(umh_list);
-static DEFINE_MUTEX(umh_list_lock);
-
 static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
 {
 	struct file_system_type *type;
@@ -134,7 +131,6 @@ static int umd_setup(struct subprocess_info *info, struct cred *new)
 	umd_info->pipe_to_umh = to_umh[1];
 	umd_info->pipe_from_umh = from_umh[0];
 	umd_info->tgid = get_pid(task_tgid(current));
-	current->flags |= PF_UMH;
 	return 0;
 }
 
@@ -182,11 +178,6 @@ int fork_usermode_driver(struct umd_info *info)
 		goto out;
 
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
-	if (!err) {
-		mutex_lock(&umh_list_lock);
-		list_add(&info->list, &umh_list);
-		mutex_unlock(&umh_list_lock);
-	}
 out:
 	if (argv)
 		argv_free(argv);
@@ -194,23 +185,4 @@ int fork_usermode_driver(struct umd_info *info)
 }
 EXPORT_SYMBOL_GPL(fork_usermode_driver);
 
-void __exit_umh(struct task_struct *tsk)
-{
-	struct umd_info *info;
-	struct pid *tgid = task_tgid(tsk);
-
-	mutex_lock(&umh_list_lock);
-	list_for_each_entry(info, &umh_list, list) {
-		if (info->tgid == tgid) {
-			list_del(&info->list);
-			mutex_unlock(&umh_list_lock);
-			goto out;
-		}
-	}
-	mutex_unlock(&umh_list_lock);
-	return;
-out:
-	if (info->cleanup)
-		info->cleanup(info);
-}
 
-- 
2.25.0

[PATCH v3 14/16] bpfilter: Take advantage of the facilities of struct pid

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:48:58

Instead of relying on the exit_umh cleanup callback use the fact a
struct pid can be tested to see if a process still exists, and that
struct pid has a wait queue that notifies when the process dies.

v1: https://lkml.kernel.org/r/87h7uydlu9.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/874kqt4owu.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/bpfilter.h     |  3 ++-
 net/bpfilter/bpfilter_kern.c | 15 +++++----------
 net/ipv4/bpfilter/sockopt.c  | 15 ++++++++-------
 3 files changed, 15 insertions(+), 18 deletions(-)
diff --git a/include/linux/bpfilter.h b/include/linux/bpfilter.h
index ec9972d822e0..9b114c718a76 100644
--- a/include/linux/bpfilter.h
+++ b/include/linux/bpfilter.h
@@ -10,6 +10,8 @@ int bpfilter_ip_set_sockopt(struct sock *sk, int optname, char __user *optval,
 			    unsigned int optlen);
 int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
 			    int __user *optlen);
+void bpfilter_umh_cleanup(struct umd_info *info);
+
 struct bpfilter_umh_ops {
 	struct umd_info info;
 	/* since ip_getsockopt() can run in parallel, serialize access to umh */
@@ -18,7 +20,6 @@ struct bpfilter_umh_ops {
 		       char __user *optval,
 		       unsigned int optlen, bool is_set);
 	int (*start)(void);
-	bool stop;
 };
 extern struct bpfilter_umh_ops bpfilter_ops;
 #endif
diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index 08ea77c2b137..9616fb7defeb 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -18,10 +18,11 @@ static void shutdown_umh(void)
 	struct umd_info *info = &bpfilter_ops.info;
 	struct pid *tgid = info->tgid;
 
-	if (bpfilter_ops.stop)
-		return;
-
-	kill_pid(tgid, SIGKILL, 1);
+	if (tgid) {
+		kill_pid(tgid, SIGKILL, 1);
+		wait_event(tgid->wait_pidfd, thread_group_exited(tgid));
+		bpfilter_umh_cleanup(info);
+	}
 }
 
 static void __stop_umh(void)
@@ -77,7 +78,6 @@ static int start_umh(void)
 	err = fork_usermode_driver(&bpfilter_ops.info);
 	if (err)
 		return err;
-	bpfilter_ops.stop = false;
 	pr_info("Loaded bpfilter_umh pid %d\n", pid_nr(bpfilter_ops.info.tgid));
 
 	/* health check that usermode process started correctly */
@@ -100,16 +100,11 @@ static int __init load_umh(void)
 		return err;
 
 	mutex_lock(&bpfilter_ops.lock);
-	if (!bpfilter_ops.stop) {
-		err = -EFAULT;
-		goto out;
-	}
 	err = start_umh();
 	if (!err && IS_ENABLED(CONFIG_INET)) {
 		bpfilter_ops.sockopt = &__bpfilter_process_sockopt;
 		bpfilter_ops.start = &start_umh;
 	}
-out:
 	mutex_unlock(&bpfilter_ops.lock);
 	if (err)
 		umd_unload_blob(&bpfilter_ops.info);
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index 56cbc43145f6..9063c6767d34 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -12,16 +12,14 @@
 struct bpfilter_umh_ops bpfilter_ops;
 EXPORT_SYMBOL_GPL(bpfilter_ops);
 
-static void bpfilter_umh_cleanup(struct umd_info *info)
+void bpfilter_umh_cleanup(struct umd_info *info)
 {
-	mutex_lock(&bpfilter_ops.lock);
-	bpfilter_ops.stop = true;
 	fput(info->pipe_to_umh);
 	fput(info->pipe_from_umh);
 	put_pid(info->tgid);
 	info->tgid = NULL;
-	mutex_unlock(&bpfilter_ops.lock);
 }
+EXPORT_SYMBOL_GPL(bpfilter_umh_cleanup);
 
 static int bpfilter_mbox_request(struct sock *sk, int optname,
 				 char __user *optval,
@@ -39,7 +37,11 @@ static int bpfilter_mbox_request(struct sock *sk, int optname,
 			goto out;
 		}
 	}
-	if (bpfilter_ops.stop) {
+	if (bpfilter_ops.info.tgid &&
+	    thread_group_exited(bpfilter_ops.info.tgid))
+		bpfilter_umh_cleanup(&bpfilter_ops.info);
+
+	if (!bpfilter_ops.info.tgid) {
 		err = bpfilter_ops.start();
 		if (err)
 			goto out;
@@ -70,9 +72,8 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname, char __user *optval,
 static int __init bpfilter_sockopt_init(void)
 {
 	mutex_init(&bpfilter_ops.lock);
-	bpfilter_ops.stop = true;
+	bpfilter_ops.info.tgid = NULL;
 	bpfilter_ops.info.driver_name = "bpfilter_umh";
-	bpfilter_ops.info.cleanup = &bpfilter_umh_cleanup;
 
 	return 0;
 }
-- 
2.25.0

[PATCH v3 12/16] umd: Track user space drivers with struct pid

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:49:03

Use struct pid instead of user space pid values that are prone to wrap
araound.

In addition track the entire thread group instead of just the first
thread that is started by exec.  There are no multi-threaded user mode
drivers today but there is nothing preclucing user drivers from being
multi-threaded, so it is just a good idea to track the entire process.

Take a reference count on the tgid's in question to make it possible
to remove exit_umh in a future change.

As a struct pid is available directly use kill_pid_info.

The prior process signalling code was iffy in using a userspace pid
known to be in the initial pid namespace and then looking up it's task
in whatever the current pid namespace is.  It worked only because
kernel threads always run in the initial pid namespace.

As the tgid is now refcounted verify the tgid is NULL at the start of
fork_usermode_driver to avoid the possibility of silent pid leaks.

v1: https://lkml.kernel.org/r/87mu4qdlv2.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/a70l4oy8.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/usermode_driver.h |  2 +-
 kernel/exit.c                   |  3 ++-
 kernel/usermode_driver.c        | 15 ++++++++++-----
 net/bpfilter/bpfilter_kern.c    | 13 +++++--------
 net/ipv4/bpfilter/sockopt.c     |  3 ++-
 5 files changed, 20 insertions(+), 16 deletions(-)
diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 97c919b7147c..45adbffb31d9 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -25,7 +25,7 @@ struct umd_info {
 	struct list_head list;
 	void (*cleanup)(struct umd_info *info);
 	struct path wd;
-	pid_t pid;
+	struct pid *tgid;
 };
 int umd_load_blob(struct umd_info *info, const void *data, size_t len);
 int umd_unload_blob(struct umd_info *info);
diff --git a/kernel/exit.c b/kernel/exit.c
index a081deea52ca..d3294b611df1 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -805,7 +805,8 @@ void __noreturn do_exit(long code)
 	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
 	exit_thread(tsk);
-	exit_umh(tsk);
+	if (group_dead)
+		exit_umh(tsk);
 
 	/*
 	 * Flush inherited counters to the parent - before the parent
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index a86798759f83..f77f8d7ce9e3 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -133,7 +133,7 @@ static int umd_setup(struct subprocess_info *info, struct cred *new)
 	set_fs_pwd(current->fs, &umd_info->wd);
 	umd_info->pipe_to_umh = to_umh[1];
 	umd_info->pipe_from_umh = from_umh[0];
-	umd_info->pid = task_pid_nr(current);
+	umd_info->tgid = get_pid(task_tgid(current));
 	current->flags |= PF_UMH;
 	return 0;
 }
@@ -146,6 +146,8 @@ static void umd_cleanup(struct subprocess_info *info)
 	if (info->retval) {
 		fput(umd_info->pipe_to_umh);
 		fput(umd_info->pipe_from_umh);
+		put_pid(umd_info->tgid);
+		umd_info->tgid = NULL;
 	}
 }
 
@@ -155,9 +157,9 @@ static void umd_cleanup(struct subprocess_info *info)
  *
  * Returns either negative error or zero which indicates success in
  * executing a usermode driver. In such case 'struct umd_info *info'
- * is populated with two pipes and a pid of the process. The caller is
+ * is populated with two pipes and a tgid of the process. The caller is
  * responsible for health check of the user process, killing it via
- * pid, and closing the pipes when user process is no longer needed.
+ * tgid, and closing the pipes when user process is no longer needed.
  */
 int fork_usermode_driver(struct umd_info *info)
 {
@@ -165,6 +167,9 @@ int fork_usermode_driver(struct umd_info *info)
 	char **argv = NULL;
 	int err;
 
+	if (WARN_ON_ONCE(info->tgid))
+		return -EBUSY;
+
 	err = -ENOMEM;
 	argv = argv_split(GFP_KERNEL, info->driver_name, NULL);
 	if (!argv)
@@ -192,11 +197,11 @@ EXPORT_SYMBOL_GPL(fork_usermode_driver);
 void __exit_umh(struct task_struct *tsk)
 {
 	struct umd_info *info;
-	pid_t pid = tsk->pid;
+	struct pid *tgid = task_tgid(tsk);
 
 	mutex_lock(&umh_list_lock);
 	list_for_each_entry(info, &umh_list, list) {
-		if (info->pid == pid) {
+		if (info->tgid == tgid) {
 			list_del(&info->list);
 			mutex_unlock(&umh_list_lock);
 			goto out;
diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index 28883b00609d..08ea77c2b137 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -15,16 +15,13 @@ extern char bpfilter_umh_end;
 
 static void shutdown_umh(void)
 {
-	struct task_struct *tsk;
+	struct umd_info *info = &bpfilter_ops.info;
+	struct pid *tgid = info->tgid;
 
 	if (bpfilter_ops.stop)
 		return;
 
-	tsk = get_pid_task(find_vpid(bpfilter_ops.info.pid), PIDTYPE_PID);
-	if (tsk) {
-		send_sig(SIGKILL, tsk, 1);
-		put_task_struct(tsk);
-	}
+	kill_pid(tgid, SIGKILL, 1);
 }
 
 static void __stop_umh(void)
@@ -48,7 +45,7 @@ static int __bpfilter_process_sockopt(struct sock *sk, int optname,
 	req.cmd = optname;
 	req.addr = (long __force __user)optval;
 	req.len = optlen;
-	if (!bpfilter_ops.info.pid)
+	if (!bpfilter_ops.info.tgid)
 		goto out;
 	n = __kernel_write(bpfilter_ops.info.pipe_to_umh, &req, sizeof(req),
 			   &pos);
@@ -81,7 +78,7 @@ static int start_umh(void)
 	if (err)
 		return err;
 	bpfilter_ops.stop = false;
-	pr_info("Loaded bpfilter_umh pid %d\n", bpfilter_ops.info.pid);
+	pr_info("Loaded bpfilter_umh pid %d\n", pid_nr(bpfilter_ops.info.tgid));
 
 	/* health check that usermode process started correctly */
 	if (__bpfilter_process_sockopt(NULL, 0, NULL, 0, 0) != 0) {
diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
index 5050de28333d..56cbc43145f6 100644
--- a/net/ipv4/bpfilter/sockopt.c
+++ b/net/ipv4/bpfilter/sockopt.c
@@ -18,7 +18,8 @@ static void bpfilter_umh_cleanup(struct umd_info *info)
 	bpfilter_ops.stop = true;
 	fput(info->pipe_to_umh);
 	fput(info->pipe_from_umh);
-	info->pid = 0;
+	put_pid(info->tgid);
+	info->tgid = NULL;
 	mutex_unlock(&bpfilter_ops.lock);
 }
 
-- 
2.25.0

[PATCH v3 16/16] umd: Stop using split_argv

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:49:08

There is exactly one argument so there is nothing to split.  All
split_argv does now is cause confusion and avoid the need for a cast
when passing a "const char *" string to call_usermodehelper_setup.

So avoid confusion and the possibility of an odd driver name causing
problems by just using a fixed argv array with a cast in the call to
call_usermodehelper_setup.

v1: https://lkml.kernel.org/r/87sged3a9n.fsf_-_@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <redacted>
---
 kernel/usermode_driver.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index cd136f86f799..0b35212ffc3d 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -160,27 +160,21 @@ static void umd_cleanup(struct subprocess_info *info)
 int fork_usermode_driver(struct umd_info *info)
 {
 	struct subprocess_info *sub_info;
-	char **argv = NULL;
+	const char *argv[] = { info->driver_name, NULL };
 	int err;
 
 	if (WARN_ON_ONCE(info->tgid))
 		return -EBUSY;
 
 	err = -ENOMEM;
-	argv = argv_split(GFP_KERNEL, info->driver_name, NULL);
-	if (!argv)
-		goto out;
-
-	sub_info = call_usermodehelper_setup(info->driver_name, argv, NULL,
-					     GFP_KERNEL,
+	sub_info = call_usermodehelper_setup(info->driver_name,
+					     (char **)argv, NULL, GFP_KERNEL,
 					     umd_setup, umd_cleanup, info);
 	if (!sub_info)
 		goto out;
 
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 out:
-	if (argv)
-		argv_free(argv);
 	return err;
 }
 EXPORT_SYMBOL_GPL(fork_usermode_driver);
-- 
2.25.0

[PATCH v3 11/16] bpfilter: Move bpfilter_umh back into init data

From: Eric W. Biederman <hidden>
Date: 2020-07-02 16:49:09

To allow for restarts 61fbf5933d42 ("net: bpfilter: restart
bpfilter_umh when error occurred") moved the blob holding the
userspace binary out of the init sections.

Now that loading the blob into a filesystem is separate from executing
the blob the blob no longer needs to live .rodata to allow for restarting.
So move the blob back to .init.rodata.

v1: https://lkml.kernel.org/r/87sgeidlvq.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87ftad4ozc.fsf_-_@x220.int.ebiederm.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <redacted>
---
 net/bpfilter/bpfilter_umh_blob.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/bpfilter/bpfilter_umh_blob.S b/net/bpfilter/bpfilter_umh_blob.S
index 9ea6100dca87..40311d10d2f2 100644
--- a/net/bpfilter/bpfilter_umh_blob.S
+++ b/net/bpfilter/bpfilter_umh_blob.S
@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-	.section .rodata, "a"
+	.section .init.rodata, "a"
 	.global bpfilter_umh_start
 bpfilter_umh_start:
 	.incbin "net/bpfilter/bpfilter_umh"
-- 
2.25.0

Re: [PATCH v3 00/16] Make the user mode driver code a better citizen

From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Date: 2020-07-02 23:52:52

On 2020/07/03 1:40, Eric W. Biederman wrote:
This is the third round of my changeset to split the user mode driver
code from the user mode helper code, and to make the code use common
facilities to get things done instead of recreating them just
for the user mode driver code.
I won't test this version, for you are ignoring my comments.

Re: [PATCH v3 13/16] exit: Factor thread_group_exited out of pidfd_poll

From: Alexei Starovoitov <hidden>
Date: 2020-07-03 20:30:30

On Thu, Jul 02, 2020 at 11:41:37AM -0500, Eric W. Biederman wrote:
quoted hunk
Create an independent helper thread_group_exited report return true
when all threads have passed exit_notify in do_exit.  AKA all of the
threads are at least zombies and might be dead or completely gone.

Create this helper by taking the logic out of pidfd_poll where
it is already tested, and adding a missing READ_ONCE on
the read of task->exit_state.

I will be changing the user mode driver code to use this same logic
to know when a user mode driver needs to be restarted.

Place the new helper thread_group_exited in kernel/exit.c and
EXPORT it so it can be used by modules.

Signed-off-by: "Eric W. Biederman" <redacted>
---
 include/linux/sched/signal.h |  2 ++
 kernel/exit.c                | 24 ++++++++++++++++++++++++
 kernel/fork.c                |  6 +-----
 3 files changed, 27 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 0ee5e696c5d8..1bad18a1d8ba 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -674,6 +674,8 @@ static inline int thread_group_empty(struct task_struct *p)
 #define delay_group_leader(p) \
 		(thread_group_leader(p) && !thread_group_empty(p))
 
+extern bool thread_group_exited(struct pid *pid);
+
 extern struct sighand_struct *__lock_task_sighand(struct task_struct *task,
 							unsigned long *flags);
 
diff --git a/kernel/exit.c b/kernel/exit.c
index d3294b611df1..a7f112feb0f6 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1713,6 +1713,30 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 }
 #endif
 
+/**
+ * thread_group_exited - check that a thread group has exited
+ * @pid: tgid of thread group to be checked.
+ *
+ * Test if thread group is has exited (all threads are zombies, dead
+ * or completely gone).
+ *
+ * Return: true if the thread group has exited. false otherwise.
+ */
+bool thread_group_exited(struct pid *pid)
+{
+	struct task_struct *task;
+	bool exited;
+
+	rcu_read_lock();
+	task = pid_task(pid, PIDTYPE_PID);
+	exited = !task ||
+		(READ_ONCE(task->exit_state) && thread_group_empty(task));
+	rcu_read_unlock();
+
+	return exited;
+}
I'm not sure why you think READ_ONCE was missing.
It's different in wait_consider_task() where READ_ONCE is needed because
of multiple checks. Here it's done once.

The rest all looks good to me. Tested with and without bpf_preload patches.
Feel free to create a frozen branch with this set.

btw I'll be offline starting tomorrow for a week.
Will catch up with threads afterwards.

Re: [PATCH v3 13/16] exit: Factor thread_group_exited out of pidfd_poll

From: Christian Brauner <hidden>
Date: 2020-07-04 16:00:56

On Thu, Jul 02, 2020 at 11:41:37AM -0500, Eric W. Biederman wrote:
Create an independent helper thread_group_exited report return true
s/report return/which reports/
when all threads have passed exit_notify in do_exit.  AKA all of the
threads are at least zombies and might be dead or completely gone.

Create this helper by taking the logic out of pidfd_poll where
it is already tested, and adding a missing READ_ONCE on
the read of task->exit_state.
I would prefer to have this comment dropped as this read_once() is not
missing as you can see from the comments elsewhere in this thread.
I will be changing the user mode driver code to use this same logic
to know when a user mode driver needs to be restarted.

Place the new helper thread_group_exited in kernel/exit.c and
EXPORT it so it can be used by modules.

Signed-off-by: "Eric W. Biederman" <redacted>
---
Minus the typos above and below, this looks good and passes the pidfd
and process test-suite.
Acked-by: Christian Brauner <redacted>

Thanks!
Christian
quoted hunk
 include/linux/sched/signal.h |  2 ++
 kernel/exit.c                | 24 ++++++++++++++++++++++++
 kernel/fork.c                |  6 +-----
 3 files changed, 27 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 0ee5e696c5d8..1bad18a1d8ba 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -674,6 +674,8 @@ static inline int thread_group_empty(struct task_struct *p)
 #define delay_group_leader(p) \
 		(thread_group_leader(p) && !thread_group_empty(p))
 
+extern bool thread_group_exited(struct pid *pid);
+
 extern struct sighand_struct *__lock_task_sighand(struct task_struct *task,
 							unsigned long *flags);
 
diff --git a/kernel/exit.c b/kernel/exit.c
index d3294b611df1..a7f112feb0f6 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1713,6 +1713,30 @@ COMPAT_SYSCALL_DEFINE5(waitid,
 }
 #endif
 
+/**
+ * thread_group_exited - check that a thread group has exited
+ * @pid: tgid of thread group to be checked.
+ *
+ * Test if thread group is has exited (all threads are zombies, dead
s/is has exited/has exited/
quoted hunk
+ * or completely gone).
+ *
+ * Return: true if the thread group has exited. false otherwise.
+ */
+bool thread_group_exited(struct pid *pid)
+{
+	struct task_struct *task;
+	bool exited;
+
+	rcu_read_lock();
+	task = pid_task(pid, PIDTYPE_PID);
+	exited = !task ||
+		(READ_ONCE(task->exit_state) && thread_group_empty(task));
+	rcu_read_unlock();
+
+	return exited;
+}
+EXPORT_SYMBOL(thread_group_exited);
+
 __weak void abort(void)
 {
 	BUG();
diff --git a/kernel/fork.c b/kernel/fork.c
index 142b23645d82..bf215af7a904 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1787,22 +1787,18 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
  */
 static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
 {
-	struct task_struct *task;
 	struct pid *pid = file->private_data;
 	__poll_t poll_flags = 0;
 
 	poll_wait(file, &pid->wait_pidfd, pts);
 
-	rcu_read_lock();
-	task = pid_task(pid, PIDTYPE_PID);
 	/*
 	 * Inform pollers only when the whole thread group exits.
 	 * If the thread group leader exits before all other threads in the
 	 * group, then poll(2) should block, similar to the wait(2) family.
 	 */
-	if (!task || (task->exit_state && thread_group_empty(task)))
+	if (thread_group_exited(pid))
 		poll_flags = EPOLLIN | EPOLLRDNORM;
-	rcu_read_unlock();
 
 	return poll_flags;
 }
-- 
2.25.0

Re: [PATCH v3 10/16] exec: Remove do_execve_file

From: Luis Chamberlain <mcgrof@kernel.org>
Date: 2020-07-08 06:35:33

On Thu, Jul 02, 2020 at 11:41:34AM -0500, Eric W. Biederman wrote:
Now that the last callser has been removed remove this code from exec.

For anyone thinking of resurrecing do_execve_file please note that
the code was buggy in several fundamental ways.

- It did not ensure the file it was passed was read-only and that
  deny_write_access had been called on it.  Which subtlely breaks
  invaniants in exec.

- The caller of do_execve_file was expected to hold and put a
  reference to the file, but an extra reference for use by exec was
  not taken so that when exec put it's reference to the file an
  underflow occured on the file reference count.
Maybe its my growing love with testing, but I'm going to have to partly
blame here that we added a new API without any respective testing.
Granted, I recall this this patch set could have used more wider review
and a bit more patience... but just mentioning this so we try to avoid
new api-without-testing with more reason in the future.

But more importantly, *how* could we have caught this? Or how can we
catch this sort of stuff better in the future?
- The point of the interface was so that a pathname did not need to
  exist.  Which breaks pathname based LSMs.
Perhaps so but this fails to do justice of the LSM consideration done
for the patch which added this during patch review [0], and I
particularly recall I called out LSM folks to bring their ray guns out at
this patch. It didn't get much attention.

Let me recap a few points I think your commit log should somehow
consider. You do as you please.

Users of shmem_kernel_file_setup() spawned out of the desire to                                                                                                      
*avoid* LSMs since it didn't make sense in their case as their inodes                                                                                                      
are never exposed to userspace. Such is the case for ipc/shm.c and                                                                                                         
security/keys/big_key.c. Refer to commit c7277090927a5 ("security: shmem:                                                                                                  
implement kernel private shmem inodes") and then commit e1832f2923ec9                                                                                                      
("ipc: use private shmem or hugetlbfs inodes for shm segments").

And the umh module approach was doing:

 a) mapping data already extracted by the kernel somehow from
    a file somehow, presumably from /lib/modules/ path somewhere, but
    again this is not visible to umc.c, as it just gets called with:
                                                                                                                                                                          
     fork_usermode_blob(void *data, size_t len, struct umh_info *info)
                                                                                                                                                                          
 b) Creating the respective tmpfs file with shmem_kernel_file_setup()
 c) Populating the file created and stuffing it with our data passed
 d) Calling do_execve_file() on it.

So, although I was hoping LSM folks would chime in for things I may have
missed during my patch review, my recollection from the patch thread was
that this becuase of a) it in theory could skip out on dealing with LSMs.

[0] https://lkml.kernel.org/r/20180509022526.hertzfpvy7apz6ny@ast-mbp               

  Luis

Re: [PATCH v3 10/16] exec: Remove do_execve_file

From: Luis Chamberlain <mcgrof@kernel.org>
Date: 2020-07-08 12:41:57

On Wed, Jul 08, 2020 at 06:35:25AM +0000, Luis Chamberlain wrote:
On Thu, Jul 02, 2020 at 11:41:34AM -0500, Eric W. Biederman wrote:
quoted
Now that the last callser has been removed remove this code from exec.

For anyone thinking of resurrecing do_execve_file please note that
the code was buggy in several fundamental ways.

- It did not ensure the file it was passed was read-only and that
  deny_write_access had been called on it.  Which subtlely breaks
  invaniants in exec.

- The caller of do_execve_file was expected to hold and put a
  reference to the file, but an extra reference for use by exec was
  not taken so that when exec put it's reference to the file an
  underflow occured on the file reference count.
Maybe its my growing love with testing, but I'm going to have to partly
blame here that we added a new API without any respective testing.
Granted, I recall this this patch set could have used more wider review
and a bit more patience... but just mentioning this so we try to avoid
new api-without-testing with more reason in the future.

But more importantly, *how* could we have caught this? Or how can we
catch this sort of stuff better in the future?
Of all the issues you pointed out with do_execve_file(), since upon
review the assumption *by design* was that LSMs/etc would pick up issues
with the file *prior* to processing, I think that this file reference
count issue comes to my attention as the more serious issue which I
wish we could address *first* before this crusade.

So I have to ask, has anyone *really tried* to give a crack at fixing
this refcount issue in a smaller way first? Alexei?

I'm not opposed to the removal of do_execve_file(), however if there
is a reproducible crash / issue with the existing user, this sledge
hammer seems a bit overkill for older kernels.

  Luis

Re: [PATCH v3 10/16] exec: Remove do_execve_file

From: Pavel Machek <hidden>
Date: 2020-07-12 21:02:56

On Thu 2020-07-02 11:41:34, Eric W. Biederman wrote:
Now that the last callser has been removed remove this code from exec.
Typo "caller".
For anyone thinking of resurrecing do_execve_file please note that
resurrecting?
the code was buggy in several fundamental ways.

- It did not ensure the file it was passed was read-only and that
  deny_write_access had been called on it.  Which subtlely breaks
  invaniants in exec.
subtly, invariants?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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