[PATCH v8 00/11] proc: modernize proc to support multiple private instances

Greetings!

Preface:
--------
This is patchset v8 to modernize procfs and make it able to support multiple
private instances per the same pid namespace.

This patchset can be applied on top of v5.4-rc7-49-g0e3f1ad80fc8


Procfs modernization:
---------------------
Historically procfs was always tied to pid namespaces, during pid
namespace creation we internally create a procfs mount for it. However,
this has the effect that all new procfs mounts are just a mirror of the
internal one, any change, any mount option update, any new future
introduction will propagate to all other procfs mounts that are in the
same pid namespace.

This may have solved several use cases in that time. However today we
face new requirements, and making procfs able to support new private
instances inside same pid namespace seems a major point. If we want to
to introduce new features and security mechanisms we have to make sure
first that we do not break existing usecases. Supporting private procfs
instances will allow to support new features and behaviour without
propagating it to all other procfs mounts.

Today procfs is more of a burden especially to some Embedded, IoT,
sandbox, container use cases. In user space we are over-mounting null
or inaccessible files on top to hide files and information. If we want
to hide pids we have to create PID namespaces otherwise mount options
propagate to all other proc mounts, changing a mount option value in one
mount will propagate to all other proc mounts. If we want to introduce
new features, then they will propagate to all other mounts too, resulting
either maybe new useful functionality or maybe breaking stuff. We have
also to note that userspace should not workaround procfs, the kernel
should just provide a sane simple interface.

In this regard several developers and maintainers pointed out that
there are problems with procfs and it has to be modernized:

"Here's another one: split up and modernize /proc." by Andy Lutomirski [1]

Discussion about kernel pointer leaks:

"And yes, as Kees and Daniel mentioned, it's definitely not just dmesg.
In fact, the primary things tend to be /proc and /sys, not dmesg
itself." By Linus Torvalds [2]

Lot of other areas in the kernel and filesystems have been updated to be
able to support private instances, devpts is one major example [3].

Which will be used for:

1) Embedded systems and IoT: usually we have one supervisor for
apps, we have some lightweight sandbox support, however if we create
pid namespaces we have to manage all the processes inside too,
where our goal is to be able to run a bunch of apps each one inside
its own mount namespace, maybe use network namespaces for vlans
setups, but right now we only want mount namespaces, without all the
other complexity. We want procfs to behave more like a real file system,
and block access to inodes that belong to other users. The 'hidepid=' will
not work since it is a shared mount option.

2) Containers, sandboxes and Private instances of file systems - devpts case
Historically, lot of file systems inside Linux kernel view when instantiated
were just a mirror of an already created and mounted filesystem. This was the
case of devpts filesystem, it seems at that time the requirements were to
optimize things and reuse the same memory, etc. This design used to work but not
anymore with today's containers, IoT, hostile environments and all the privacy
challenges that Linux faces.

In that regards, devpts was updated so that each new mounts is a total
independent file system by the following patches:

"devpts: Make each mount of devpts an independent filesystem" by
Eric W. Biederman [3] [4]

3) Linux Security Modules have multiple ptrace paths inside some
subsystems, however inside procfs, the implementation does not guarantee
that the ptrace() check which triggers the security_ptrace_check() hook
will always run. We have the 'hidepid' mount option that can be used to
force the ptrace_may_access() check inside has_pid_permissions() to run.
The problem is that 'hidepid' is per pid namespace and not attached to
the mount point, any remount or modification of 'hidepid' will propagate
to all other procfs mounts.

This also does not allow to support Yama LSM easily in desktop and user
sessions. Yama ptrace scope which restricts ptrace and some other
syscalls to be allowed only on inferiors, can be updated to have a
per-task context, where the context will be inherited during fork(),
clone() and preserved across execve(). If we support multiple private
procfs instances, then we may force the ptrace_may_access() on
/proc/<pids>/ to always run inside that new procfs instances. This will
allow to specifiy on user sessions if we should populate procfs with
pids that the user can ptrace or not.

By using Yama ptrace scope, some restricted users will only be able to see
inferiors inside /proc, they won't even be able to see their other
processes. Some software like Chromium, Firefox's crash handler, Wine
and others are already using Yama to restrict which processes can be
ptracable. With this change this will give the possibility to restrict
/proc/<pids>/ but more importantly this will give desktop users a
generic and usuable way to specifiy which users should see all processes
and which user can not.

Side notes:

* This covers the lack of seccomp where it is not able to parse
arguments, it is easy to install a seccomp filter on direct syscalls
that operate on pids, however /proc/<pid>/ is a Linux ABI using
filesystem syscalls. With this change all LSMs should be able to analyze
open/read/write/close... on /proc/<pid>/

4) This will allow to implement new features either in kernel or
userspace without having to worry about procfs.
In containers, sandboxes, etc we have workarounds to hide some /proc
inodes, this should be supported natively without doing extra complex
work, the kernel should be able to support sane options that work with
today and future Linux use cases.

5) Creation of new superblock with all procfs options for each procfs
mount will fix the ignoring of mount options. The problem is that the
second mount of procfs in the same pid namespace ignores the mount
options. The mount options are ignored without error until procfs is
remounted.

Before:

# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0

# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0

+++ exited with 0 +++

# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0
proc /tmp/proc proc rw,relatime,hidepid=2 0 0

# mount -o remount,hidepid=1 -t proc proc /tmp/proc

# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=1 0 0
proc /tmp/proc proc rw,relatime,hidepid=1 0 0

After:

# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0

# mount -o hidepid=1 -t proc proc /tmp/proc

# grep ^proc /proc/mounts
proc /proc proc rw,relatime,hidepid=2 0 0
proc /tmp/proc proc rw,relatime,hidepid=1 0 0


Introduced changes:
-------------------
Each mount of procfs creates a separate procfs instance with its own
mount options.

This series adds few new mount options:

* New 'hidepid=4' mount option to show only ptraceable processes in the procfs.
This allows to support lightweight sandboxes in Embedded Linux, also
solves the case for LSM where now with this mount option, we make sure
that they have a ptrace path in procfs.

* 'subset=pidfs' that allows to hide non-pid inodes from procfs. It can be used
in containers and sandboxes, as these are already trying to hide and block
access to procfs inodes anyway.


ChangeLog:
----------
# v8:
* Started using RCU lock to clean dcache entries as Linus Torvalds suggested.

# v7:
* 'pidonly=1' renamed to 'subset=pidfs' as Alexey Dobriyan suggested.
* HIDEPID_* moved to uapi/ as they are user interface to mount().
  Suggested-by Alexey Dobriyan [off-list ref]

# v6:
* 'hidepid=' and 'gid=' mount options are moved from pid namespace to superblock.
* 'newinstance' mount option removed as Eric W. Biederman suggested.
   Mount of procfs always creates a new instance.
* 'limit_pids' renamed to 'hidepid=3'.
* I took into account the comment of Linus Torvalds [7].
* Documentation added.

# v5:
* Fixed a bug that caused a problem with the Fedora boot.
* The 'pidonly' option is visible among the mount options.

# v2:
* Renamed mount options to 'newinstance' and 'pids='
   Suggested-by: Andy Lutomirski [off-list ref]
* Fixed order of commit, Suggested-by: Andy Lutomirski [off-list ref]
* Many bug fixes.

# v1:
* Removed 'unshared' mount option and replaced it with 'limit_pids'
   which is attached to the current procfs mount.
   Suggested-by Andy Lutomirski [off-list ref]
* Do not fill dcache with pid entries that we can not ptrace.
* Many bug fixes.


References:
-----------
[1] https://lists.linuxfoundation.org/pipermail/ksummit-discuss/2017-January/004215.html
[2] http://www.openwall.com/lists/kernel-hardening/2017/10/05/5
[3] https://lwn.net/Articles/689539/
[4] http://lxr.free-electrons.com/source/Documentation/filesystems/devpts.txt?v=3.14
[5] https://lkml.org/lkml/2017/5/2/407
[6] https://lkml.org/lkml/2017/5/3/357
[7] https://lkml.org/lkml/2018/5/11/505


Alexey Gladkov (11):
  proc: Rename struct proc_fs_info to proc_fs_opts
  proc: add proc_fs_info struct to store proc information
  proc: move /proc/{self|thread-self} dentries to proc_fs_info
  proc: move hide_pid, pid_gid from pid_namespace to proc_fs_info
  proc: add helpers to set and get proc hidepid and gid mount options
  proc: support mounting procfs instances inside same pid namespace
  proc: flush task dcache entries from all procfs instances
  proc: instantiate only pids that we can ptrace on 'hidepid=4' mount
    option
  proc: add option to mount only a pids subset
  docs: proc: add documentation for "hidepid=4" and "subset=pidfs"
    options and new mount behavior
  proc: Move hidepid values to uapi as they are user interface to mount

 Documentation/filesystems/proc.txt |  53 +++++++++++
 fs/locks.c                         |   6 +-
 fs/proc/base.c                     |  66 ++++++++++----
 fs/proc/generic.c                  |   9 ++
 fs/proc/inode.c                    |  21 +++--
 fs/proc/internal.h                 |  30 ++++++
 fs/proc/root.c                     | 141 +++++++++++++++++++++++------
 fs/proc/self.c                     |   4 +-
 fs/proc/thread_self.c              |   6 +-
 fs/proc_namespace.c                |  14 +--
 include/linux/pid_namespace.h      |  14 +--
 include/linux/proc_fs.h            |  25 ++++-
 include/uapi/linux/proc_fs.h       |  13 +++
 13 files changed, 324 insertions(+), 78 deletions(-)
 create mode 100644 include/uapi/linux/proc_fs.h

-- 
2.24.1

This is a preparation patch that adds proc_fs_info to be able to store
different procfs options and informations. Right now some mount options
are stored inside the pid namespace which makes it hard to change or
modernize procfs without affecting pid namespaces. Plus we do want to
treat proc as more of a real mount point and filesystem. procfs is part
of Linux API where it offers some features using filesystem syscalls and
in order to support some features where we are able to have multiple
instances of procfs, each one with its mount options inside the same pid
namespace, we have to separate these procfs instances.

This is the same feature that was also added to other Linux interfaces
like devpts in order to support containers, sandboxes, and to have
multiple instances of devpts filesystem [1].

[1] https://elixir.bootlin.com/linux/v3.4/source/Documentation/filesystems/devpts.txt

Cc: Kees Cook <redacted>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/locks.c              |  6 +++--
 fs/proc/base.c          |  8 +++++--
 fs/proc/inode.c         |  4 ++--
 fs/proc/root.c          | 49 +++++++++++++++++++++++++++--------------
 include/linux/proc_fs.h | 11 ++++++++-
 5 files changed, 54 insertions(+), 24 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 6970f55daf54..21200e3005e4 100644
--- a/fs/locks.c
+++ b/fs/locks.c

@@ -2795,7 +2795,8 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
 {
 	struct inode *inode = NULL;
 	unsigned int fl_pid;
-	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
+	struct proc_fs_info *fs_info = proc_sb_info(file_inode(f->file)->i_sb);
+	struct pid_namespace *proc_pidns = fs_info->pid_ns;
 
 	fl_pid = locks_translate_pid(fl, proc_pidns);
 	/*

@@ -2873,7 +2874,8 @@ static int locks_show(struct seq_file *f, void *v)
 {
 	struct locks_iterator *iter = f->private;
 	struct file_lock *fl, *bfl;
-	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
+	struct proc_fs_info *fs_info = proc_sb_info(file_inode(f->file)->i_sb);
+	struct pid_namespace *proc_pidns = fs_info->pid_ns;
 
 	fl = hlist_entry(v, struct file_lock, fl_link);
 

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..672e71c52dbd 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -3243,6 +3243,7 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 {
 	struct task_struct *task;
 	unsigned tgid;
+	struct proc_fs_info *fs_info;
 	struct pid_namespace *ns;
 	struct dentry *result = ERR_PTR(-ENOENT);
 

@@ -3250,7 +3251,8 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 	if (tgid == ~0U)
 		goto out;
 
-	ns = dentry->d_sb->s_fs_info;
+	fs_info = proc_sb_info(dentry->d_sb);
+	ns = fs_info->pid_ns;
 	rcu_read_lock();
 	task = find_task_by_pid_ns(tgid, ns);
 	if (task)

@@ -3538,6 +3540,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
 	struct task_struct *task;
 	struct task_struct *leader = get_proc_task(dir);
 	unsigned tid;
+	struct proc_fs_info *fs_info;
 	struct pid_namespace *ns;
 	struct dentry *result = ERR_PTR(-ENOENT);
 

@@ -3548,7 +3551,8 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
 	if (tid == ~0U)
 		goto out;
 
-	ns = dentry->d_sb->s_fs_info;
+	fs_info = proc_sb_info(dentry->d_sb);
+	ns = fs_info->pid_ns;
 	rcu_read_lock();
 	task = find_task_by_pid_ns(tid, ns);
 	if (task)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index dbe43a50caf2..b631608dfbcc 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c

@@ -104,8 +104,8 @@ void __init proc_init_kmemcache(void)
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
 {
-	struct super_block *sb = root->d_sb;
-	struct pid_namespace *pid = sb->s_fs_info;
+	struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
+	struct pid_namespace *pid = fs_info->pid_ns;
 
 	if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
 		seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 0b7c8dffc9ae..d449f095f0f7 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -30,7 +30,7 @@
 #include "internal.h"
 
 struct proc_fs_context {
-	struct pid_namespace	*pid_ns;
+	struct proc_fs_info	*fs_info;
 	unsigned int		mask;
 	int			hidepid;
 	int			gid;

@@ -97,7 +97,8 @@ static void proc_apply_options(struct super_block *s,
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 {
-	struct pid_namespace *pid_ns = get_pid_ns(s->s_fs_info);
+	struct proc_fs_context *ctx = fc->fs_private;
+	struct pid_namespace *pid_ns = get_pid_ns(ctx->fs_info->pid_ns);
 	struct inode *root_inode;
 	int ret;
 

@@ -145,7 +146,8 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 static int proc_reconfigure(struct fs_context *fc)
 {
 	struct super_block *sb = fc->root->d_sb;
-	struct pid_namespace *pid = sb->s_fs_info;
+	struct proc_fs_info *fs_info = proc_sb_info(sb);
+	struct pid_namespace *pid = fs_info->pid_ns;
 
 	sync_filesystem(sb);
 

@@ -157,14 +159,14 @@ static int proc_get_tree(struct fs_context *fc)
 {
 	struct proc_fs_context *ctx = fc->fs_private;
 
-	return get_tree_keyed(fc, proc_fill_super, ctx->pid_ns);
+	return get_tree_keyed(fc, proc_fill_super, ctx->fs_info);
 }
 
 static void proc_fs_context_free(struct fs_context *fc)
 {
 	struct proc_fs_context *ctx = fc->fs_private;
 
-	put_pid_ns(ctx->pid_ns);
+	put_pid_ns(ctx->fs_info->pid_ns);
 	kfree(ctx);
 }
 

@@ -178,14 +180,27 @@ static const struct fs_context_operations proc_fs_context_ops = {
 static int proc_init_fs_context(struct fs_context *fc)
 {
 	struct proc_fs_context *ctx;
+	struct pid_namespace *pid_ns;
 
 	ctx = kzalloc(sizeof(struct proc_fs_context), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 
-	ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
+	pid_ns = get_pid_ns(task_active_pid_ns(current));
+
+	if (!pid_ns->proc_mnt) {
+		ctx->fs_info = kzalloc(sizeof(struct proc_fs_info), GFP_KERNEL);
+		if (!ctx->fs_info) {
+			kfree(ctx);
+			return -ENOMEM;
+		}
+		ctx->fs_info->pid_ns = pid_ns;
+	} else {
+		ctx->fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb);
+	}
+
 	put_user_ns(fc->user_ns);
-	fc->user_ns = get_user_ns(ctx->pid_ns->user_ns);
+	fc->user_ns = get_user_ns(ctx->fs_info->pid_ns->user_ns);
 	fc->fs_private = ctx;
 	fc->ops = &proc_fs_context_ops;
 	return 0;

@@ -193,15 +208,15 @@ static int proc_init_fs_context(struct fs_context *fc)
 
 static void proc_kill_sb(struct super_block *sb)
 {
-	struct pid_namespace *ns;
+	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
-	ns = (struct pid_namespace *)sb->s_fs_info;
-	if (ns->proc_self)
-		dput(ns->proc_self);
-	if (ns->proc_thread_self)
-		dput(ns->proc_thread_self);
+	if (fs_info->pid_ns->proc_self)
+		dput(fs_info->pid_ns->proc_self);
+	if (fs_info->pid_ns->proc_thread_self)
+		dput(fs_info->pid_ns->proc_thread_self);
 	kill_anon_super(sb);
-	put_pid_ns(ns);
+	put_pid_ns(fs_info->pid_ns);
+	kfree(fs_info);
 }
 
 static struct file_system_type proc_fs_type = {

@@ -314,10 +329,10 @@ int pid_ns_prepare_proc(struct pid_namespace *ns)
 	}
 
 	ctx = fc->fs_private;
-	if (ctx->pid_ns != ns) {
-		put_pid_ns(ctx->pid_ns);
+	if (ctx->fs_info->pid_ns != ns) {
+		put_pid_ns(ctx->fs_info->pid_ns);
 		get_pid_ns(ns);
-		ctx->pid_ns = ns;
+		ctx->fs_info->pid_ns = ns;
 	}
 
 	mnt = fc_mount(fc);

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index a705aa2d03f9..2d79489e55aa 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -12,6 +12,15 @@ struct proc_dir_entry;
 struct seq_file;
 struct seq_operations;
 
+struct proc_fs_info {
+	struct pid_namespace *pid_ns;
+};
+
+static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
 #ifdef CONFIG_PROC_FS
 
 typedef int (*proc_write_t)(struct file *, char *, size_t);

@@ -146,7 +155,7 @@ int open_related_ns(struct ns_common *ns,
 /* get the associated pid namespace for a file in procfs */
 static inline struct pid_namespace *proc_pid_ns(const struct inode *inode)
 {
-	return inode->i_sb->s_fs_info;
+	return proc_sb_info(inode->i_sb)->pid_ns;
 }
 
 #endif /* _LINUX_PROC_FS_H */

-- 
2.24.1

This is a preparation patch that moves /proc/{self|thread-self} dentries
to be stored inside procfs fs_info struct instead of making them per pid
namespace. Since we want to support multiple procfs instances we need to
make sure that these dentries are also per-superblock instead of
per-pidns, unmounting a private procfs won't clash with other procfs
mounts.

Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/base.c                | 5 +++--
 fs/proc/root.c                | 8 ++++----
 fs/proc/self.c                | 4 ++--
 fs/proc/thread_self.c         | 6 +++---
 include/linux/pid_namespace.h | 4 +---
 include/linux/proc_fs.h       | 2 ++
 6 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 672e71c52dbd..1eb366ad8b06 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -3316,6 +3316,7 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
 int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct tgid_iter iter;
+	struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
 	struct pid_namespace *ns = proc_pid_ns(file_inode(file));
 	loff_t pos = ctx->pos;
 

@@ -3323,13 +3324,13 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 		return 0;
 
 	if (pos == TGID_OFFSET - 2) {
-		struct inode *inode = d_inode(ns->proc_self);
+		struct inode *inode = d_inode(fs_info->proc_self);
 		if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
 			return 0;
 		ctx->pos = pos = pos + 1;
 	}
 	if (pos == TGID_OFFSET - 1) {
-		struct inode *inode = d_inode(ns->proc_thread_self);
+		struct inode *inode = d_inode(fs_info->proc_thread_self);
 		if (!dir_emit(ctx, "thread-self", 11, inode->i_ino, DT_LNK))
 			return 0;
 		ctx->pos = pos = pos + 1;

diff --git a/fs/proc/root.c b/fs/proc/root.c
index d449f095f0f7..637e26cc795e 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -210,10 +210,10 @@ static void proc_kill_sb(struct super_block *sb)
 {
 	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
-	if (fs_info->pid_ns->proc_self)
-		dput(fs_info->pid_ns->proc_self);
-	if (fs_info->pid_ns->proc_thread_self)
-		dput(fs_info->pid_ns->proc_thread_self);
+	if (fs_info->proc_self)
+		dput(fs_info->proc_self);
+	if (fs_info->proc_thread_self)
+		dput(fs_info->proc_thread_self);
 	kill_anon_super(sb);
 	put_pid_ns(fs_info->pid_ns);
 	kfree(fs_info);

diff --git a/fs/proc/self.c b/fs/proc/self.c
index 57c0a1047250..846fc2b7c8a8 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c

@@ -36,7 +36,7 @@ static unsigned self_inum __ro_after_init;
 int proc_setup_self(struct super_block *s)
 {
 	struct inode *root_inode = d_inode(s->s_root);
-	struct pid_namespace *ns = proc_pid_ns(root_inode);
+	struct proc_fs_info *fs_info = proc_sb_info(s);
 	struct dentry *self;
 	int ret = -ENOMEM;
 	

@@ -62,7 +62,7 @@ int proc_setup_self(struct super_block *s)
 	if (ret)
 		pr_err("proc_fill_super: can't allocate /proc/self\n");
 	else
-		ns->proc_self = self;
+		fs_info->proc_self = self;
 
 	return ret;
 }

diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
index f61ae53533f5..2493cbbdfa6f 100644
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c

@@ -36,7 +36,7 @@ static unsigned thread_self_inum __ro_after_init;
 int proc_setup_thread_self(struct super_block *s)
 {
 	struct inode *root_inode = d_inode(s->s_root);
-	struct pid_namespace *ns = proc_pid_ns(root_inode);
+	struct proc_fs_info *fs_info = proc_sb_info(s);
 	struct dentry *thread_self;
 	int ret = -ENOMEM;
 

@@ -60,9 +60,9 @@ int proc_setup_thread_self(struct super_block *s)
 	inode_unlock(root_inode);
 
 	if (ret)
-		pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
+		pr_err("proc_fill_super: can't allocate /proc/thread-self\n");
 	else
-		ns->proc_thread_self = thread_self;
+		fs_info->proc_thread_self = thread_self;
 
 	return ret;
 }

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 49538b172483..f91a8bf6e09e 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h

@@ -31,9 +31,7 @@ struct pid_namespace {
 	unsigned int level;
 	struct pid_namespace *parent;
 #ifdef CONFIG_PROC_FS
-	struct vfsmount *proc_mnt;
-	struct dentry *proc_self;
-	struct dentry *proc_thread_self;
+	struct vfsmount *proc_mnt; /* Internal proc mounted during each new pidns */
 #endif
 #ifdef CONFIG_BSD_PROCESS_ACCT
 	struct fs_pin *bacct;

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 2d79489e55aa..59162988998e 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -14,6 +14,8 @@ struct seq_operations;
 
 struct proc_fs_info {
 	struct pid_namespace *pid_ns;
+	struct dentry *proc_self;        /* For /proc/self */
+	struct dentry *proc_thread_self; /* For /proc/thread-self */
 };
 
 static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)

-- 
2.24.1

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

This is a preparation patch that moves /proc/{self|thread-self} dentries
to be stored inside procfs fs_info struct instead of making them per pid
namespace. Since we want to support multiple procfs instances we need to
make sure that these dentries are also per-superblock instead of
per-pidns,

The changelog makes perfect sense so far...

unmounting a private procfs won't clash with other procfs
mounts.

This doesn't parse as part of the previous sentence.  I'm also not
convinced that this really involves unmounting per se.  Maybe just
delete these words.

On Mon, Feb 10, 2020 at 10:23:23AM -0800, Andy Lutomirski wrote:

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

quoted

This is a preparation patch that moves /proc/{self|thread-self} dentries
to be stored inside procfs fs_info struct instead of making them per pid
namespace. Since we want to support multiple procfs instances we need to
make sure that these dentries are also per-superblock instead of
per-pidns,

The changelog makes perfect sense so far...

quoted

unmounting a private procfs won't clash with other procfs
mounts.

This doesn't parse as part of the previous sentence.  I'm also not
convinced that this really involves unmounting per se.  Maybe just
delete these words.

Sure. I will remove this part.

-- 
Rgrds, legion

This allows to flush dcache entries of a task on multiple procfs mounts
per pid namespace.

The RCU lock is used because the number of reads at the task exit time
is much larger than the number of procfs mounts.

Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/base.c                | 20 +++++++++++++++-----
 fs/proc/root.c                | 27 ++++++++++++++++++++++++++-
 include/linux/pid_namespace.h |  2 ++
 include/linux/proc_fs.h       |  2 ++
 4 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4ccb280a3e79..24b7c620ded3 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -3133,7 +3133,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = {
 	.permission	= proc_pid_permission,
 };
 
-static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
+static void proc_flush_task_mnt_root(struct dentry *mnt_root, pid_t pid, pid_t tgid)
 {
 	struct dentry *dentry, *leader, *dir;
 	char buf[10 + 1];

@@ -3142,7 +3142,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
 	name.name = buf;
 	name.len = snprintf(buf, sizeof(buf), "%u", pid);
 	/* no ->d_hash() rejects on procfs */
-	dentry = d_hash_and_lookup(mnt->mnt_root, &name);
+	dentry = d_hash_and_lookup(mnt_root, &name);
 	if (dentry) {
 		d_invalidate(dentry);
 		dput(dentry);

@@ -3153,7 +3153,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
 
 	name.name = buf;
 	name.len = snprintf(buf, sizeof(buf), "%u", tgid);
-	leader = d_hash_and_lookup(mnt->mnt_root, &name);
+	leader = d_hash_and_lookup(mnt_root, &name);
 	if (!leader)
 		goto out;
 

@@ -3208,14 +3208,24 @@ void proc_flush_task(struct task_struct *task)
 	int i;
 	struct pid *pid, *tgid;
 	struct upid *upid;
+	struct dentry *mnt_root;
+	struct proc_fs_info *fs_info;
 
 	pid = task_pid(task);
 	tgid = task_tgid(task);
 
 	for (i = 0; i <= pid->level; i++) {
 		upid = &pid->numbers[i];
-		proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
-					tgid->numbers[i].nr);
+
+		rcu_read_lock();
+		list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) {
+			mnt_root = fs_info->m_super->s_root;
+			proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr);
+		}
+		rcu_read_unlock();
+
+		mnt_root = upid->ns->proc_mnt->mnt_root;
+		proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr);
 	}
 }
 

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 5d5cba4c899b..e2bb015da1a8 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -149,7 +149,22 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	if (ret) {
 		return ret;
 	}
-	return proc_setup_thread_self(s);
+
+	ret = proc_setup_thread_self(s);
+	if (ret) {
+		return ret;
+	}
+
+	/*
+	 * back reference to flush dcache entries at process exit time.
+	 */
+	ctx->fs_info->m_super = s;
+
+	spin_lock(&pid_ns->proc_mounts_lock);
+	list_add_tail_rcu(&ctx->fs_info->pidns_entry, &pid_ns->proc_mounts);
+	spin_unlock(&pid_ns->proc_mounts_lock);
+
+	return 0;
 }
 
 static int proc_reconfigure(struct fs_context *fc)

@@ -211,10 +226,17 @@ static void proc_kill_sb(struct super_block *sb)
 {
 	struct proc_fs_info *fs_info = proc_sb_info(sb);
 
+	spin_lock(&fs_info->pid_ns->proc_mounts_lock);
+	list_del_rcu(&fs_info->pidns_entry);
+	spin_unlock(&fs_info->pid_ns->proc_mounts_lock);
+
+	synchronize_rcu();
+
 	if (fs_info->proc_self)
 		dput(fs_info->proc_self);
 	if (fs_info->proc_thread_self)
 		dput(fs_info->proc_thread_self);
+
 	kill_anon_super(sb);
 	put_pid_ns(fs_info->pid_ns);
 	kfree(fs_info);

@@ -336,6 +358,9 @@ int pid_ns_prepare_proc(struct pid_namespace *ns)
 		ctx->fs_info->pid_ns = ns;
 	}
 
+	spin_lock_init(&ns->proc_mounts_lock);
+	INIT_LIST_HEAD_RCU(&ns->proc_mounts);
+
 	mnt = fc_mount(fc);
 	put_fs_context(fc);
 	if (IS_ERR(mnt))

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 66f47f1afe0d..c36af1dfd862 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h

@@ -26,6 +26,8 @@ struct pid_namespace {
 	struct pid_namespace *parent;
 #ifdef CONFIG_PROC_FS
 	struct vfsmount *proc_mnt; /* Internal proc mounted during each new pidns */
+	spinlock_t proc_mounts_lock;
+	struct list_head proc_mounts; /* list of separated procfs mounts */
 #endif
 #ifdef CONFIG_BSD_PROCESS_ACCT
 	struct fs_pin *bacct;

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 5f0b1b7e4271..f307940f8311 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -20,6 +20,8 @@ enum {
 };
 
 struct proc_fs_info {
+	struct list_head pidns_entry;    /* Node in procfs_mounts of a pidns */
+	struct super_block *m_super;
 	struct pid_namespace *pid_ns;
 	struct dentry *proc_self;        /* For /proc/self */
 	struct dentry *proc_thread_self; /* For /proc/thread-self */

-- 
2.24.1

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

This allows to flush dcache entries of a task on multiple procfs mounts
per pid namespace.

The RCU lock is used because the number of reads at the task exit time
is much larger than the number of procfs mounts.

Ok, this looks better to me than the previous version.

But that may be the "pee-in-the-snow" effect, and I _really_ want
others to take a good look at the whole series.

The right people seem to be cc'd, but this is pretty core, and /proc
has a tendency to cause interesting issues because of how it's
involved in a lot of areas indirectly.

Al, Oleg, Andy, Eric?

             Linus

On Mon, Feb 10, 2020 at 09:46:26AM -0800, Linus Torvalds wrote:

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

quoted

This allows to flush dcache entries of a task on multiple procfs mounts
per pid namespace.

The RCU lock is used because the number of reads at the task exit time
is much larger than the number of procfs mounts.

Ok, this looks better to me than the previous version.

But that may be the "pee-in-the-snow" effect, and I _really_ want
others to take a good look at the whole series.

The right people seem to be cc'd, but this is pretty core, and /proc
has a tendency to cause interesting issues because of how it's
involved in a lot of areas indirectly.

Al, Oleg, Andy, Eric?

Will check tonight (ears-deep in sorting out the old branches right now)

On Mon, Feb 10, 2020 at 04:05:15PM +0100, Alexey Gladkov wrote:

... which can block

 		dput(dentry);

... and so can this

+		rcu_read_lock();
+		list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) {
+			mnt_root = fs_info->m_super->s_root;
+			proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr);

... making that more than slightly unsafe.

On Tue, Feb 11, 2020 at 10:45:53PM +0000, Al Viro wrote:

On Mon, Feb 10, 2020 at 04:05:15PM +0100, Alexey Gladkov wrote:

quoted

This allows to flush dcache entries of a task on multiple procfs mounts
per pid namespace.

The RCU lock is used because the number of reads at the task exit time
is much larger than the number of procfs mounts.

Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/base.c                | 20 +++++++++++++++-----
 fs/proc/root.c                | 27 ++++++++++++++++++++++++++-
 include/linux/pid_namespace.h |  2 ++
 include/linux/proc_fs.h       |  2 ++
 4 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4ccb280a3e79..24b7c620ded3 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -3133,7 +3133,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = {
 	.permission	= proc_pid_permission,
 };
 
-static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
+static void proc_flush_task_mnt_root(struct dentry *mnt_root, pid_t pid, pid_t tgid)
 {
 	struct dentry *dentry, *leader, *dir;
 	char buf[10 + 1];

@@ -3142,7 +3142,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
 	name.name = buf;
 	name.len = snprintf(buf, sizeof(buf), "%u", pid);
 	/* no ->d_hash() rejects on procfs */
-	dentry = d_hash_and_lookup(mnt->mnt_root, &name);
+	dentry = d_hash_and_lookup(mnt_root, &name);
 	if (dentry) {
 		d_invalidate(dentry);

... which can block

quoted

 		dput(dentry);

... and so can this

quoted

+		rcu_read_lock();
+		list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) {
+			mnt_root = fs_info->m_super->s_root;
+			proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr);

... making that more than slightly unsafe.

I see. So, I can't use rcu locks here as well as spinlocks.
Thanks!

-- 
Rgrds, legion

Signed-off-by: Alexey Gladkov <redacted>
---
 Documentation/filesystems/proc.txt | 53 ++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 99ca040e3f90..4741fd092f36 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt

@@ -50,6 +50,8 @@ Table of Contents
   4	Configuring procfs
   4.1	Mount options
 
+  5	Filesystem behavior
+
 ------------------------------------------------------------------------------
 Preface
 ------------------------------------------------------------------------------

@@ -2021,6 +2023,7 @@ The following mount options are supported:
 
 	hidepid=	Set /proc/<pid>/ access mode.
 	gid=		Set the group authorized to learn processes information.
+	subset=		Show only the specified subset of procfs.
 
 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
 (default).

@@ -2042,6 +2045,56 @@ information about running processes, whether some daemon runs with elevated
 privileges, whether other user runs some sensitive program, whether other users
 run any program at all, etc.
 
+hidepid=4 means that procfs should only contain /proc/<pid>/ directories
+that the caller can ptrace.
+
 gid= defines a group authorized to learn processes information otherwise
 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
 information about processes information, just add identd to this group.
+
+subset=pidfs hides all top level files and directories in the procfs that
+are not related to tasks.
+
+------------------------------------------------------------------------------
+5 Filesystem behavior
+------------------------------------------------------------------------------
+
+Originally, before the advent of pid namepsace, procfs was a global file
+system. It means that there was only one procfs instance in the system.
+
+When pid namespace was added, a separate procfs instance was mounted in
+each pid namespace. So, procfs mount options are global among all
+mountpoints within the same namespace.
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+
+# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
+mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
++++ exited with 0 +++
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+proc /tmp/proc proc rw,relatime,hidepid=2 0 0
+
+and only after remounting procfs mount options will change at all
+mountpoints.
+
+# mount -o remount,hidepid=1 -t proc proc /tmp/proc
+
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=1 0 0
+proc /tmp/proc proc rw,relatime,hidepid=1 0 0
+
+This behavior is different from the behavior of other filesystems.
+
+The new procfs behavior is more like other filesystems. Each procfs mount
+creates a new procfs instance. Mount options affect own procfs instance.
+It means that it became possible to have several procfs instances
+displaying tasks with different filtering options in one pid namespace.
+
+# mount -o hidepid=2 -t proc proc /proc
+# mount -o hidepid=1 -t proc proc /tmp/proc
+# grep ^proc /proc/mounts
+proc /proc proc rw,relatime,hidepid=2 0 0
+proc /tmp/proc proc rw,relatime,hidepid=1 0 0

-- 
2.24.1

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

I have a couple of minor nits here.

First, perhaps we could stop using magic numbers and use words.
hidepid=ptraceable is actually comprehensible, whereas hidepid=4
requires looking up what '4' means.

Second, there is PTRACE_MODE_ATTACH and PTRACE_MODE_READ.  Which is it?

+
 gid= defines a group authorized to learn processes information otherwise
 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
 information about processes information, just add identd to this group.

How is this better than just creating an entirely separate mount a
different hidepid and a different gid owning it?  In any event,
usually gid= means that this gid is the group owner of inodes.  Let's
call it something different.  gid_override_hidepid might be credible.
But it's also really weird -- do different groups really see different
contents when they read a directory?

On Mon, Feb 10, 2020 at 10:29:23AM -0800, Andy Lutomirski wrote:

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

quoted

Signed-off-by: Alexey Gladkov <redacted>
---
 Documentation/filesystems/proc.txt | 53 ++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 99ca040e3f90..4741fd092f36 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt

@@ -50,6 +50,8 @@ Table of Contents
   4    Configuring procfs
   4.1  Mount options

+  5    Filesystem behavior
+
 ------------------------------------------------------------------------------
 Preface
 ------------------------------------------------------------------------------

@@ -2021,6 +2023,7 @@ The following mount options are supported:

        hidepid=        Set /proc/<pid>/ access mode.
        gid=            Set the group authorized to learn processes information.
+       subset=         Show only the specified subset of procfs.

 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
 (default).

@@ -2042,6 +2045,56 @@ information about running processes, whether some daemon runs with elevated
 privileges, whether other user runs some sensitive program, whether other users
 run any program at all, etc.

+hidepid=4 means that procfs should only contain /proc/<pid>/ directories
+that the caller can ptrace.

I have a couple of minor nits here.

First, perhaps we could stop using magic numbers and use words.
hidepid=ptraceable is actually comprehensible, whereas hidepid=4
requires looking up what '4' means.

Do you mean to add string aliases for the values?

hidepid=0 == hidepid=default
hidepid=1 == hidepid=restrict
hidepid=2 == hidepid=ownonly
hidepid=4 == hidepid=ptraceable

Something like that ?

Second, there is PTRACE_MODE_ATTACH and PTRACE_MODE_READ.  Which is it?

This is PTRACE_MODE_READ.

quoted

+
 gid= defines a group authorized to learn processes information otherwise
 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
 information about processes information, just add identd to this group.

How is this better than just creating an entirely separate mount a
different hidepid and a different gid owning it?

I'm not sure I understand the question. Now you cannot have two proc with
different hidepid in the same pid_namespace. 

In any event,
usually gid= means that this gid is the group owner of inodes.  Let's
call it something different.  gid_override_hidepid might be credible.
But it's also really weird -- do different groups really see different
contents when they read a directory?

If you use hidepid=2,gid=wheel options then the user is not in the wheel
group will see only their processes and the user in the wheel group will
see whole tree. The gid= is a kind of whitelist for hidepid=1|2.

-- 
Rgrds, legion

Suggested-by: Alexey Dobriyan <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 include/linux/proc_fs.h      |  9 +--------
 include/uapi/linux/proc_fs.h | 13 +++++++++++++
 2 files changed, 14 insertions(+), 8 deletions(-)
 create mode 100644 include/uapi/linux/proc_fs.h

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 3ad0a47c3556..f2b4a411d371 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -7,19 +7,12 @@
 
 #include <linux/types.h>
 #include <linux/fs.h>
+#include <uapi/linux/proc_fs.h>
 
 struct proc_dir_entry;
 struct seq_file;
 struct seq_operations;
 
-/* definitions for hide_pid field */
-enum {
-	HIDEPID_OFF	  = 0,
-	HIDEPID_NO_ACCESS = 1,
-	HIDEPID_INVISIBLE = 2,
-	HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */
-};
-
 /* definitions for proc mount option pidonly */
 enum {
 	PROC_PIDONLY_OFF = 0,

diff --git a/include/uapi/linux/proc_fs.h b/include/uapi/linux/proc_fs.h
new file mode 100644
index 000000000000..1e3374efffe2
--- /dev/null
+++ b/include/uapi/linux/proc_fs.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_PROC_FS_H
+#define _UAPI_PROC_FS_H
+
+/* definitions for hide_pid field */
+enum {
+	HIDEPID_OFF           = 0,
+	HIDEPID_NO_ACCESS     = 1,
+	HIDEPID_INVISIBLE     = 2,
+	HIDEPID_NOT_PTRACABLE = 4,
+};
+
+#endif

-- 
2.24.1

This allows to hide all files and directories in the procfs that are not
related to tasks.

Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/generic.c       |  9 +++++++++
 fs/proc/inode.c         |  7 +++++++
 fs/proc/internal.h      | 10 ++++++++++
 fs/proc/root.c          | 36 ++++++++++++++++++++++++++++++++++++
 include/linux/proc_fs.h |  7 +++++++
 5 files changed, 69 insertions(+)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 64e9ee1b129e..6f6517d63053 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c

@@ -267,6 +267,11 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
 struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
 		unsigned int flags)
 {
+	struct proc_fs_info *fs_info = proc_sb_info(dir->i_sb);
+
+	if (proc_fs_pidonly(fs_info) == PROC_PIDONLY_ON)
+		return ERR_PTR(-ENOENT);
+
 	return proc_lookup_de(dir, dentry, PDE(dir));
 }
 

@@ -323,6 +328,10 @@ int proc_readdir_de(struct file *file, struct dir_context *ctx,
 int proc_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct inode *inode = file_inode(file);
+	struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);
+
+	if (proc_fs_pidonly(fs_info) == PROC_PIDONLY_ON)
+		return 1;
 
 	return proc_readdir_de(file, ctx, PDE(inode));
 }

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 70b722fb8811..f35eef117775 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c

@@ -114,6 +114,9 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
 	if (hidepid != HIDEPID_OFF)
 		seq_printf(seq, ",hidepid=%u", hidepid);
 
+	if (proc_fs_pidonly(fs_info) != PROC_PIDONLY_OFF)
+		seq_printf(seq, ",subset=pidfs");
+
 	return 0;
 }
 

@@ -333,12 +336,16 @@ proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr,
 
 static int proc_reg_open(struct inode *inode, struct file *file)
 {
+	struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);
 	struct proc_dir_entry *pde = PDE(inode);
 	int rv = 0;
 	typeof_member(struct file_operations, open) open;
 	typeof_member(struct file_operations, release) release;
 	struct pde_opener *pdeo;
 
+	if (proc_fs_pidonly(fs_info) == PROC_PIDONLY_ON)
+		return -ENOENT;
+
 	/*
 	 * Ensure that
 	 * 1) PDE's ->release hook will be called no matter what

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index ff2f274b2e0d..e2c729267317 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h

@@ -126,6 +126,11 @@ static inline void proc_fs_set_hide_pid(struct proc_fs_info *fs_info, int hide_p
 	fs_info->hide_pid = hide_pid;
 }
 
+static inline void proc_fs_set_pidonly(struct proc_fs_info *fs_info, int value)
+{
+	fs_info->pidonly = value;
+}
+
 static inline void proc_fs_set_pid_gid(struct proc_fs_info *fs_info, kgid_t gid)
 {
 	fs_info->pid_gid = gid;

@@ -141,6 +146,11 @@ static inline kgid_t proc_fs_pid_gid(struct proc_fs_info *fs_info)
 	return fs_info->pid_gid;
 }
 
+static inline int proc_fs_pidonly(struct proc_fs_info *fs_info)
+{
+	return fs_info->pidonly;
+}
+
 void task_dump_owner(struct task_struct *task, umode_t mode,
 		     kuid_t *ruid, kgid_t *rgid);
 

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 5e27bb31f125..4dce77639c2b 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -34,16 +34,19 @@ struct proc_fs_context {
 	unsigned int		mask;
 	int			hidepid;
 	int			gid;
+	int			pidonly;
 };
 
 enum proc_param {
 	Opt_gid,
 	Opt_hidepid,
+	Opt_subset,
 };
 
 static const struct fs_parameter_spec proc_param_specs[] = {
 	fsparam_u32("gid",	Opt_gid),
 	fsparam_u32("hidepid",	Opt_hidepid),
+	fsparam_string("subset",	Opt_subset),
 	{}
 };
 

@@ -61,6 +64,30 @@ valid_hidepid(unsigned int value)
 		value == HIDEPID_NOT_PTRACABLE);
 }
 
+static inline int
+proc_parse_subset_param(struct fs_context *fc, char *value)
+{
+	struct proc_fs_context *ctx = fc->fs_private;
+
+	while (value) {
+		char *ptr = strchr(value, ',');
+
+		if (ptr != NULL)
+			*ptr++ = '\0';
+
+		if (*value != '\0') {
+			if (!strcmp(value, "pidfs")) {
+				ctx->pidonly = PROC_PIDONLY_ON;
+			} else {
+				return invalf(fc, "proc: unsupported subset option - %s\n", value);
+			}
+		}
+		value = ptr;
+	}
+
+	return 0;
+}
+
 static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	struct proc_fs_context *ctx = fc->fs_private;

@@ -82,6 +109,11 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		ctx->hidepid = result.uint_32;
 		break;
 
+	case Opt_subset:
+		if (proc_parse_subset_param(fc, param->string) < 0)
+			return -EINVAL;
+		break;
+
 	default:
 		return -EINVAL;
 	}

@@ -102,6 +134,7 @@ static void proc_apply_options(struct proc_fs_info *fs_info,
 
 		proc_fs_set_pid_gid(fs_info, proc_fs_pid_gid(pidns_fs_info));
 		proc_fs_set_hide_pid(fs_info, proc_fs_hide_pid(pidns_fs_info));
+		proc_fs_set_pidonly(fs_info, proc_fs_pidonly(pidns_fs_info));
 	}
 
 	if (ctx->mask & (1 << Opt_gid))

@@ -109,6 +142,9 @@ static void proc_apply_options(struct proc_fs_info *fs_info,
 
 	if (ctx->mask & (1 << Opt_hidepid))
 		proc_fs_set_hide_pid(fs_info, ctx->hidepid);
+
+	if (ctx->mask & (1 << Opt_subset))
+		proc_fs_set_pidonly(fs_info, ctx->pidonly);
 }
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 6822548405a7..3ad0a47c3556 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -20,6 +20,12 @@ enum {
 	HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */
 };
 
+/* definitions for proc mount option pidonly */
+enum {
+	PROC_PIDONLY_OFF = 0,
+	PROC_PIDONLY_ON  = 1,
+};
+
 struct proc_fs_info {
 	struct list_head pidns_entry;    /* Node in procfs_mounts of a pidns */
 	struct super_block *m_super;

@@ -28,6 +34,7 @@ struct proc_fs_info {
 	struct dentry *proc_thread_self; /* For /proc/thread-self */
 	kgid_t pid_gid;
 	int hide_pid;
+	int pidonly;
 };
 
 static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)

-- 
2.24.1

If "hidepid=4" mount option is set then do not instantiate pids that
we can not ptrace. "hidepid=4" means that procfs should only contain
pids that the caller can ptrace.

Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/base.c          | 15 +++++++++++++++
 fs/proc/root.c          | 14 +++++++++++---
 include/linux/proc_fs.h |  1 +
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 24b7c620ded3..49937d54e745 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -699,6 +699,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,
 				 struct task_struct *task,
 				 int hide_pid_min)
 {
+	/*
+	 * If 'hidpid' mount option is set force a ptrace check,
+	 * we indicate that we are using a filesystem syscall
+	 * by passing PTRACE_MODE_READ_FSCREDS
+	 */
+	if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE)
+		return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
+
 	if (proc_fs_hide_pid(fs_info) < hide_pid_min)
 		return true;
 	if (in_group_p(proc_fs_pid_gid(fs_info)))

@@ -3271,7 +3279,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
 	if (!task)
 		goto out;
 
+	/* Limit procfs to only ptracable tasks */
+	if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE) {
+		if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+			goto out_put_task;
+	}
+
 	result = proc_pid_instantiate(dentry, task, NULL);
+out_put_task:
 	put_task_struct(task);
 out:
 	return result;

diff --git a/fs/proc/root.c b/fs/proc/root.c
index e2bb015da1a8..5e27bb31f125 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -52,6 +52,15 @@ static const struct fs_parameter_description proc_fs_parameters = {
 	.specs		= proc_param_specs,
 };
 
+static inline int
+valid_hidepid(unsigned int value)
+{
+	return (value == HIDEPID_OFF ||
+		value == HIDEPID_NO_ACCESS ||
+		value == HIDEPID_INVISIBLE ||
+		value == HIDEPID_NOT_PTRACABLE);
+}
+
 static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	struct proc_fs_context *ctx = fc->fs_private;

@@ -68,10 +77,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		break;
 
 	case Opt_hidepid:
+		if (!valid_hidepid(result.uint_32))
+			return invalf(fc, "proc: unknown value of hidepid.\n");
 		ctx->hidepid = result.uint_32;
-		if (ctx->hidepid < HIDEPID_OFF ||
-		    ctx->hidepid > HIDEPID_INVISIBLE)
-			return invalf(fc, "proc: hidepid value must be between 0 and 2.\n");
 		break;
 
 	default:

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index f307940f8311..6822548405a7 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -17,6 +17,7 @@ enum {
 	HIDEPID_OFF	  = 0,
 	HIDEPID_NO_ACCESS = 1,
 	HIDEPID_INVISIBLE = 2,
+	HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */
 };
 
 struct proc_fs_info {

-- 
2.24.1

On Monday, February 10, 2020 3:05 PM, Alexey Gladkov [off-list ref] wrote:

Is there a reason new option is "4" instead of "3"? The order 1..2..4 may be
confusing for people.

Jordan

On Mon, Feb 10, 2020 at 04:29:31PM +0000, Jordan Glover wrote:

On Monday, February 10, 2020 3:05 PM, Alexey Gladkov [off-list ref] wrote:

quoted

If "hidepid=4" mount option is set then do not instantiate pids that
we can not ptrace. "hidepid=4" means that procfs should only contain
pids that the caller can ptrace.

Cc: Kees Cook keescook@chromium.org
Cc: Andy Lutomirski luto@kernel.org
Signed-off-by: Djalal Harouni tixxdz@gmail.com
Signed-off-by: Alexey Gladkov gladkov.alexey@gmail.com

fs/proc/base.c | 15 +++++++++++++++
fs/proc/root.c | 14 +++++++++++---
include/linux/proc_fs.h | 1 +
3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 24b7c620ded3..49937d54e745 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -699,6 +699,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,

struct task_struct *task,
int hide_pid_min)
{

-   /*
-   -   If 'hidpid' mount option is set force a ptrace check,
-   -   we indicate that we are using a filesystem syscall
-   -   by passing PTRACE_MODE_READ_FSCREDS
-   */
-   if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE)
-         return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);


-   if (proc_fs_hide_pid(fs_info) < hide_pid_min)
    return true;
    if (in_group_p(proc_fs_pid_gid(fs_info)))
    @@ -3271,7 +3279,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
    if (!task)
    goto out;

-   /* Limit procfs to only ptracable tasks */
-   if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE) {
-         if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))


-         	goto out_put_task;


-   }
-   result = proc_pid_instantiate(dentry, task, NULL);
    +out_put_task:
    put_task_struct(task);
    out:
    return result;
    diff --git a/fs/proc/root.c b/fs/proc/root.c
    index e2bb015da1a8..5e27bb31f125 100644
    --- a/fs/proc/root.c
    +++ b/fs/proc/root.c
    @@ -52,6 +52,15 @@ static const struct fs_parameter_description proc_fs_parameters = {
    .specs = proc_param_specs,
    };

    +static inline int
    +valid_hidepid(unsigned int value)
    +{

-   return (value == HIDEPID_OFF ||
-         value == HIDEPID_NO_ACCESS ||


-         value == HIDEPID_INVISIBLE ||


-         value == HIDEPID_NOT_PTRACABLE);



+}
+
static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct proc_fs_context *ctx = fc->fs_private;

@@ -68,10 +77,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)

break;

case Opt_hidepid:

-         if (!valid_hidepid(result.uint_32))


-         	return invalf(fc, "proc: unknown value of hidepid.\\n");
          ctx->hidepid = result.uint_32;



-         if (ctx->hidepid < HIDEPID_OFF ||


-             ctx->hidepid > HIDEPID_INVISIBLE)


-         	return invalf(fc, "proc: hidepid value must be between 0 and 2.\\n");
          break;



default:

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index f307940f8311..6822548405a7 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -17,6 +17,7 @@ enum {

HIDEPID_OFF = 0,
HIDEPID_NO_ACCESS = 1,
HIDEPID_INVISIBLE = 2,

-   HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */

Is there a reason new option is "4" instead of "3"? The order 1..2..4 may be
confusing for people.

This is just mask. For now hidepid values are mutually exclusive, but
since it moved to uapi, I thought it would be good if there was an
opportunity to combine values.

-- 
Rgrds, legion

This is a cleaning patch to add helpers to set and get proc mount
options instead of directly using them. This make it easy to track
what's happening and easy to update in future.

Cc: Kees Cook <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/base.c     |  6 +++---
 fs/proc/inode.c    | 11 +++++++----
 fs/proc/internal.h | 20 ++++++++++++++++++++
 fs/proc/root.c     |  8 ++++----
 4 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index caca1929fee1..4ccb280a3e79 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -699,9 +699,9 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,
 				 struct task_struct *task,
 				 int hide_pid_min)
 {
-	if (fs_info->hide_pid < hide_pid_min)
+	if (proc_fs_hide_pid(fs_info) < hide_pid_min)
 		return true;
-	if (in_group_p(fs_info->pid_gid))
+	if (in_group_p(proc_fs_pid_gid(fs_info)))
 		return true;
 	return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
 }

@@ -720,7 +720,7 @@ static int proc_pid_permission(struct inode *inode, int mask)
 	put_task_struct(task);
 
 	if (!has_perms) {
-		if (fs_info->hide_pid == HIDEPID_INVISIBLE) {
+		if (proc_fs_hide_pid(fs_info) == HIDEPID_INVISIBLE) {
 			/*
 			 * Let's make getdents(), stat(), and open()
 			 * consistent with each other.  If a process

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index b90c233e5968..70b722fb8811 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c

@@ -105,11 +105,14 @@ void __init proc_init_kmemcache(void)
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
 {
 	struct proc_fs_info *fs_info = proc_sb_info(root->d_sb);
+	int hidepid = proc_fs_hide_pid(fs_info);
+	kgid_t gid = proc_fs_pid_gid(fs_info);
 
-	if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID))
-		seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid));
-	if (fs_info->hide_pid != HIDEPID_OFF)
-		seq_printf(seq, ",hidepid=%u", fs_info->hide_pid);
+	if (!gid_eq(gid, GLOBAL_ROOT_GID))
+		seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, gid));
+
+	if (hidepid != HIDEPID_OFF)
+		seq_printf(seq, ",hidepid=%u", hidepid);
 
 	return 0;
 }

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index cd0c8d5ce9a1..ff2f274b2e0d 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h

@@ -121,6 +121,26 @@ static inline struct task_struct *get_proc_task(const struct inode *inode)
 	return get_pid_task(proc_pid(inode), PIDTYPE_PID);
 }
 
+static inline void proc_fs_set_hide_pid(struct proc_fs_info *fs_info, int hide_pid)
+{
+	fs_info->hide_pid = hide_pid;
+}
+
+static inline void proc_fs_set_pid_gid(struct proc_fs_info *fs_info, kgid_t gid)
+{
+	fs_info->pid_gid = gid;
+}
+
+static inline int proc_fs_hide_pid(struct proc_fs_info *fs_info)
+{
+	return fs_info->hide_pid;
+}
+
+static inline kgid_t proc_fs_pid_gid(struct proc_fs_info *fs_info)
+{
+	return fs_info->pid_gid;
+}
+
 void task_dump_owner(struct task_struct *task, umode_t mode,
 		     kuid_t *ruid, kgid_t *rgid);
 

diff --git a/fs/proc/root.c b/fs/proc/root.c
index 1ca47d446aa4..efd76c004e86 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -91,14 +91,14 @@ static void proc_apply_options(struct super_block *s,
 
 	if (pid_ns->proc_mnt) {
 		struct proc_fs_info *fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb);
-		ctx->fs_info->pid_gid = fs_info->pid_gid;
-		ctx->fs_info->hide_pid = fs_info->hide_pid;
+		proc_fs_set_pid_gid(ctx->fs_info, proc_fs_pid_gid(fs_info));
+		proc_fs_set_hide_pid(ctx->fs_info, proc_fs_hide_pid(fs_info));
 	}
 
 	if (ctx->mask & (1 << Opt_gid))
-		ctx->fs_info->pid_gid = make_kgid(user_ns, ctx->gid);
+		proc_fs_set_pid_gid(ctx->fs_info, make_kgid(user_ns, ctx->gid));
 	if (ctx->mask & (1 << Opt_hidepid))
-		ctx->fs_info->hide_pid = ctx->hidepid;
+		proc_fs_set_hide_pid(ctx->fs_info, ctx->hidepid);
 }
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)

-- 
2.24.1

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

This is a cleaning patch to add helpers to set and get proc mount
options instead of directly using them. This make it easy to track
what's happening and easy to update in future.

On a cursory inspection, this looks like it obfuscates the code, and I
don't see where it does something useful later in the series.  What is
this abstraction for?

--Andy

On Mon, Feb 10, 2020 at 10:30:45AM -0800, Andy Lutomirski wrote:

On Mon, Feb 10, 2020 at 7:06 AM Alexey Gladkov [off-list ref] wrote:

quoted

This is a cleaning patch to add helpers to set and get proc mount
options instead of directly using them. This make it easy to track
what's happening and easy to update in future.

On a cursory inspection, this looks like it obfuscates the code, and I
don't see where it does something useful later in the series.  What is
this abstraction for?

To be honest, this part is from Djalal Harouni. For me, these wrappers
exist for a slight increase in readability.

I will not cry if you tell me to remove them :)

-- 
Rgrds, legion

This patch allows to have multiple procfs instances inside the
same pid namespace. The aim here is lightweight sandboxes, and to allow
that we have to modernize procfs internals.

1) The main aim of this work is to have on embedded systems one
supervisor for apps. Right now we have some lightweight sandbox support,
however if we create pid namespacess we have to manages all the
processes inside too, where our goal is to be able to run a bunch of
apps each one inside its own mount namespace without being able to
notice each other. We only want to use mount namespaces, and we want
procfs to behave more like a real mount point.

2) Linux Security Modules have multiple ptrace paths inside some
subsystems, however inside procfs, the implementation does not guarantee
that the ptrace() check which triggers the security_ptrace_check() hook
will always run. We have the 'hidepid' mount option that can be used to
force the ptrace_may_access() check inside has_pid_permissions() to run.
The problem is that 'hidepid' is per pid namespace and not attached to
the mount point, any remount or modification of 'hidepid' will propagate
to all other procfs mounts.

This also does not allow to support Yama LSM easily in desktop and user
sessions. Yama ptrace scope which restricts ptrace and some other
syscalls to be allowed only on inferiors, can be updated to have a
per-task context, where the context will be inherited during fork(),
clone() and preserved across execve(). If we support multiple private
procfs instances, then we may force the ptrace_may_access() on
/proc/<pids>/ to always run inside that new procfs instances. This will
allow to specifiy on user sessions if we should populate procfs with
pids that the user can ptrace or not.

By using Yama ptrace scope, some restricted users will only be able to see
inferiors inside /proc, they won't even be able to see their other
processes. Some software like Chromium, Firefox's crash handler, Wine
and others are already using Yama to restrict which processes can be
ptracable. With this change this will give the possibility to restrict
/proc/<pids>/ but more importantly this will give desktop users a
generic and usuable way to specifiy which users should see all processes
and which users can not.

Side notes:
* This covers the lack of seccomp where it is not able to parse
arguments, it is easy to install a seccomp filter on direct syscalls
that operate on pids, however /proc/<pid>/ is a Linux ABI using
filesystem syscalls. With this change LSMs should be able to analyze
open/read/write/close...

In the new patchset version I removed the 'newinstance' option
as Eric W. Biederman suggested.

Cc: Kees Cook <redacted>
Cc: "Eric W. Biederman" <redacted>
Signed-off-by: Alexey Gladkov <redacted>
---
 fs/proc/root.c | 41 ++++++++++++++++++-----------------------
 1 file changed, 18 insertions(+), 23 deletions(-)

diff --git a/fs/proc/root.c b/fs/proc/root.c
index efd76c004e86..5d5cba4c899b 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c

@@ -82,7 +82,7 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	return 0;
 }
 
-static void proc_apply_options(struct super_block *s,
+static void proc_apply_options(struct proc_fs_info *fs_info,
 			       struct fs_context *fc,
 			       struct pid_namespace *pid_ns,
 			       struct user_namespace *user_ns)

@@ -90,15 +90,17 @@ static void proc_apply_options(struct super_block *s,
 	struct proc_fs_context *ctx = fc->fs_private;
 
 	if (pid_ns->proc_mnt) {
-		struct proc_fs_info *fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb);
-		proc_fs_set_pid_gid(ctx->fs_info, proc_fs_pid_gid(fs_info));
-		proc_fs_set_hide_pid(ctx->fs_info, proc_fs_hide_pid(fs_info));
+		struct proc_fs_info *pidns_fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb);
+
+		proc_fs_set_pid_gid(fs_info, proc_fs_pid_gid(pidns_fs_info));
+		proc_fs_set_hide_pid(fs_info, proc_fs_hide_pid(pidns_fs_info));
 	}
 
 	if (ctx->mask & (1 << Opt_gid))
-		proc_fs_set_pid_gid(ctx->fs_info, make_kgid(user_ns, ctx->gid));
+		proc_fs_set_pid_gid(fs_info, make_kgid(user_ns, ctx->gid));
+
 	if (ctx->mask & (1 << Opt_hidepid))
-		proc_fs_set_hide_pid(ctx->fs_info, ctx->hidepid);
+		proc_fs_set_hide_pid(fs_info, ctx->hidepid);
 }
 
 static int proc_fill_super(struct super_block *s, struct fs_context *fc)

@@ -108,7 +110,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc)
 	struct inode *root_inode;
 	int ret;
 
-	proc_apply_options(s, fc, pid_ns, current_user_ns());
+	proc_apply_options(ctx->fs_info, fc, pid_ns, current_user_ns());
 
 	/* User space would break if executables or devices appear on proc */
 	s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;