This is a note to let you know that I've just added the patch titled
drm: Lock pointer access in drm_master_release()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-lock-pointer-access-in-drm_master_release.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c336a5ee984708db4826ef9e47d184e638e29717 Mon Sep 17 00:00:00 2001
From: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Date: Wed, 9 Jun 2021 17:21:19 +0800
Subject: drm: Lock pointer access in drm_master_release()
From: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
commit c336a5ee984708db4826ef9e47d184e638e29717 upstream.
This patch eliminates the following smatch warning:
drivers/gpu/drm/drm_auth.c:320 drm_master_release() warn: unlocked access 'master' (line 318) expected lock '&dev->master_mutex'
The 'file_priv->master' field should be protected by the mutex lock to
'&dev->master_mutex'. This is because other processes can concurrently
modify this field and free the current 'file_priv->master'
pointer. This could result in a use-after-free error when 'master' is
dereferenced in subsequent function calls to
'drm_legacy_lock_master_cleanup()' or to 'drm_lease_revoke()'.
An example of a scenario that would produce this error can be seen
from a similar bug in 'drm_getunique()' that was reported by Syzbot:
https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803
In the Syzbot report, another process concurrently acquired the
device's master mutex in 'drm_setmaster_ioctl()', then overwrote
'fpriv->master' in 'drm_new_set_master()'. The old value of
'fpriv->master' was subsequently freed before the mutex was unlocked.
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210609092119.173590-1-desmondcheongzx@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_auth.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -314,9 +314,10 @@ int drm_master_open(struct drm_file *fil
void drm_master_release(struct drm_file *file_priv)
{
struct drm_device *dev = file_priv->minor->dev;
- struct drm_master *master = file_priv->master;
+ struct drm_master *master;
mutex_lock(&dev->master_mutex);
+ master = file_priv->master;
if (file_priv->magic)
idr_remove(&file_priv->master->magic_map, file_priv->magic);
Patches currently in stable-queue which might be from desmondcheongzx@xxxxxxxxx are
queue-5.10/drm-fix-use-after-free-read-in-drm_getunique.patch
queue-5.10/drm-lock-pointer-access-in-drm_master_release.patch
