In em28xx_v4l2_init(), if an error occurs after video_register_device() succeeds, the unregister_dev error path unregisters the video devices and drops the initial v4l2_dev reference, but leaves dev->v4l2 set. An em28xx_v4l2_open() call already in progress (such as from v4l_id) that blocked on dev->lock while em28xx_v4l2_init() held it will then find dev->v4l2 still non-NULL and succeed on an unregistered node instead of returning -ENODEV. When the device is later disconnected, em28xx_v4l2_fini() also sees dev->v4l2 is still set and calls v4l2_device_put() a second time, dropping the refcount to zero and freeing v4l2 while v4l_id still holds it, causing a slab-use-after-free in v4l2_open(). Fix this by clearing dev->v4l2 under dev->lock in the unregister_dev error path of em28xx_v4l2_init(). Fixes: 288254383674 ("media: em28xx: use v4l2_device release callback") Cc: stable@vger.kernel.org Reported-by: syzbot+1a7507a194fff09e5c44@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=1a7507a194fff09e5c44 Signed-off-by: Diego Fernando Mancera Gomez --- Changes in v2: - Drop the non-standard 'Assisted-by: Gemini' trailer that failed checkpatch. Note: compile-tested drivers/media/usb/em28xx/em28xx_video.o with allmodconfig (no warnings); not runtime-tested locally against the syzbot reproducer. drivers/media/usb/em28xx/em28xx-video.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c index 84424284d486..f78325a41124 100644 --- a/drivers/media/usb/em28xx/em28xx-video.c +++ b/drivers/media/usb/em28xx/em28xx-video.c @@ -3129,6 +3129,12 @@ static int em28xx_v4l2_init(struct em28xx *dev) vb2_video_unregister_device(&v4l2->vdev); } + /* + * Clear dev->v4l2 to prevent an in-progress em28xx_v4l2_open() from + * succeeding on an unregistered node (returning -ENODEV instead) and + * to prevent em28xx_v4l2_fini() from tearing down the instance again. + */ + dev->v4l2 = NULL; mutex_unlock(&dev->lock); /* -- 2.56.1