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| author | Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> | 2021-06-08 19:04:36 +0800 |
|---|---|---|
| committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2021-06-08 18:18:58 +0200 |
| commit | b436acd1cf7fac0ba987abd22955d98025c80c2b (patch) | |
| tree | 0b7130c261bc7b56dcfd51907200e8839e7ce925 | |
| parent | 8a11e84b8056c9daa0ea9d6dbb4d75382fb4a8e0 (diff) | |
| download | linux-b436acd1cf7fac0ba987abd22955d98025c80c2b.tar.gz | |
drm: Fix use-after-free read in drm_getunique()
There is a time-of-check-to-time-of-use error in drm_getunique() due
to retrieving file_priv->master prior to locking the device's master
mutex.
An example can be seen in the crash report of the use-after-free error
found by Syzbot:
https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803
In the report, the master pointer was used after being freed. This is
because another process had 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.
To fix this, we lock the device's master mutex before retrieving the
pointer from from fpriv->master. This patch passes the Syzbot
reproducer test.
Reported-by: syzbot+c3a706cec1ea99e1c693@syzkaller.appspotmail.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/20210608110436.239583-1-desmondcheongzx@gmail.com
| -rw-r--r-- | drivers/gpu/drm/drm_ioctl.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index d273d1a8603a9..495a4767a4430 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -118,17 +118,18 @@ int drm_getunique(struct drm_device *dev, void *data, struct drm_file *file_priv) { struct drm_unique *u = data; - struct drm_master *master = file_priv->master; + struct drm_master *master; - mutex_lock(&master->dev->master_mutex); + mutex_lock(&dev->master_mutex); + master = file_priv->master; if (u->unique_len >= master->unique_len) { if (copy_to_user(u->unique, master->unique, master->unique_len)) { - mutex_unlock(&master->dev->master_mutex); + mutex_unlock(&dev->master_mutex); return -EFAULT; } } u->unique_len = master->unique_len; - mutex_unlock(&master->dev->master_mutex); + mutex_unlock(&dev->master_mutex); return 0; } |