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authorDesmond Cheong Zhi Xi <desmondcheongzx@gmail.com>2021-06-09 17:21:19 +0800
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-06-10 12:22:02 +0200
commitc336a5ee984708db4826ef9e47d184e638e29717 (patch)
tree7959ebffcd91998b5b807f2aa1e1659b84d5799a /drivers
parentc8a570443943304cac2e4186dbce6989b6c2b8b5 (diff)
drm: Lock pointer access in drm_master_release()
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@oracle.com> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20210609092119.173590-1-desmondcheongzx@gmail.com
Diffstat (limited to 'drivers')
-rw-r--r--drivers/gpu/drm/drm_auth.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index f2d46b7ac6f9..232abbba3686 100644
--- 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 *file_priv)
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);