On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
Argh. Are you able to uncover what userspace is doing here?
So far, my test cases are:
1) self: open, write, close: allowed
2) self: open, clone thread. thread: change privileges, write, close: allowed
3) self: open, give to privileged process. privileged process: write: reject
--
Kees Cook
On Mon, Jun 14, 2021 at 08:32:35AM -0700, Kees Cook wrote:
On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
quoted
I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
I found getpidcon() in libselinux:
https://github.com/SELinuxProject/selinux/blob/master/libselinux/src/procattr.c#L159
quoted
06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
Argh. Are you able to uncover what userspace is doing here?
It looks like this is a case of attempting to _read_ the attr file, and
the new opener check was requiring the opener/target relationship pass
the mm_access() checks, which is clearly too strict.
So far, my test cases are:
1) self: open, write, close: allowed
2) self: open, clone thread. thread: change privileges, write, close: allowed
3) self: open, give to privileged process. privileged process: write: reject
I've now added:
4) self: open privileged process's attr, read, close: allowed
Can folks please test this patch to double-check?
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7118ebe38fa6..7c55301674e0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2676,7 +2676,14 @@ static int proc_pident_readdir(struct file *file, struct dir_context *ctx,
#ifdef CONFIG_SECURITY
static int proc_pid_attr_open(struct inode *inode, struct file *file)
{
- return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
+ struct mm_struct *mm = __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
+
+ /* Reads do not require mm_struct access. */
+ if (IS_ERR(mm))
+ mm = NULL;
+
+ file->private_data = mm;
+ return 0;
}
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,@@ -2709,7 +2716,7 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
int rv;
/* A task may only write when it was the opener. */
- if (file->private_data != current->mm)
+ if (!file->private_data || file->private_data != current->mm)
return -EPERM;
rcu_read_lock();
Wheee.
--
Kees Cook
On 6/14/2021 8:32 AM, Kees Cook wrote:
On Mon, Jun 14, 2021 at 06:02:34PM +0800, youling257 wrote:
quoted
I used mainline kernel on android, this patch cause "failed to retrieve pid context" problem.
06-14 02:15:51.165 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1682) failed to retrieve pid context.
06-14 02:15:51.166 1685 1685 E ServiceManager: add_service('batteryproperties',1) uid=0 - PERMISSION DENIED
06-14 02:15:51.166 1682 1682 I ServiceManager: addService() batteryproperties failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.197 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1695) failed to retrieve pid context.
06-14 02:15:51.197 1685 1685 E ServiceManager: add_service('android.security.keystore',1) uid=1017 - PERMISSION DENIED
06-14 02:15:51.198 1695 1695 I ServiceManager: addService() android.security.keystore failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.207 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1708) failed to retrieve pid context.
06-14 02:15:51.207 1685 1685 E ServiceManager: add_service('android.service.gatekeeper.IGateKeeperService',1) uid=1000 - PERMISSION DENIED
06-14 02:15:51.207 1708 1708 I ServiceManager: addService() android.service.gatekeeper.IGateKeeperService failed (err -1 - no service manager yet?). Retrying...
06-14 02:15:51.275 1685 1685 E ServiceManager: SELinux: getpidcon(pid=1693) failed to retrieve pid context.
06-14 02:15:51.275 1692 1692 I cameraserver: ServiceManager: 0xf6d309e0
06-14 02:15:51.275 1685 1685 E ServiceManager: add_service('drm.drmManager',1) uid=1019 - PERMISSION DENIED
06-14 02:15:51.276 1693 1693 I ServiceManager: addService() drm.drmManager failed (err -1 - no service manager yet?). Retrying...
Argh. Are you able to uncover what userspace is doing here?
So far, my test cases are:
1) self: open, write, close: allowed
2) self: open, clone thread. thread: change privileges, write, close: allowed
3) self: open, give to privileged process. privileged process: write: reject
I found an issue under Smack where a privileged process opened
/proc/self/attr/smack/current, wrote to it successfully, then tried
to write to it again, which failed because the cred has changed.
That's not a common use case. The usual case is open, write, close.
If ServiceManager is assuming that it can leave a descriptor open
while manipulations are in progress it could encounter the same kind
of problem.
On Mon, Jun 14, 2021 at 9:45 AM Kees Cook [off-list ref] wrote:
/* A task may only write when it was the opener. */
- if (file->private_data != current->mm)
+ if (!file->private_data || file->private_data != current->mm)
I don't think this is necessary.
If file->private_data is NULL, then the old test for private_data !=
current->mm will still work just fine.
Because if you can fool kernel threads to do the write for you, you
have bigger security issues than that test.
Linus