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authorDesmond Cheong Zhi Xi <desmondcheongzx@gmail.com>2021-06-08 14:04:36 +0300
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-06-08 19:18:58 +0300
commitb436acd1cf7fac0ba987abd22955d98025c80c2b (patch)
tree0b7130c261bc7b56dcfd51907200e8839e7ce925 /drivers/gpu
parent8a11e84b8056c9daa0ea9d6dbb4d75382fb4a8e0 (diff)
downloadlinux-b436acd1cf7fac0ba987abd22955d98025c80c2b.tar.xz
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
Diffstat (limited to 'drivers/gpu')
-rw-r--r--drivers/gpu/drm/drm_ioctl.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index d273d1a8603a..495a4767a443 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;
}