Re: [PATCH v3 3/3] media: uvcvideo: Lock video streams and queues while unregistering

[Sakari Ailus]

Hi Ricardo,

On Tue, Nov 21, 2023 at 07:53:50PM +0000, Ricardo Ribalda wrote:
> From: Guenter Roeck <linux@xxxxxxxxxxxx>
> 
> The call to uvc_disconnect() is not protected by any mutex.
> This means it can and will be called while other accesses to the video
> device are in progress. This can cause all kinds of race conditions,
> including crashes such as the following.
> 
> usb 1-4: USB disconnect, device number 3
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 0 PID: 5633 Comm: V4L2CaptureThre Not tainted 4.19.113-08536-g5d29ca36db06 #1
> Hardware name: GOOGLE Edgar, BIOS Google_Edgar.7287.167.156 03/25/2019
> RIP: 0010:usb_ifnum_to_if+0x29/0x40
> Code: <...>
> RSP: 0018:ffffa46f42a47a80 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff904a396c9000
> RDX: ffff904a39641320 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: ffffa46f42a47a80 R08: 0000000000000002 R09: 0000000000000000
> R10: 0000000000009975 R11: 0000000000000009 R12: 0000000000000000
> R13: ffff904a396b3800 R14: ffff904a39e88000 R15: 0000000000000000
> FS: 00007f396448e700(0000) GS:ffff904a3ba00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 000000016cb46000 CR4: 00000000001006f0
> Call Trace:
>  usb_hcd_alloc_bandwidth+0x1ee/0x30f
>  usb_set_interface+0x1a3/0x2b7
>  uvc_video_start_transfer+0x29b/0x4b8 [uvcvideo]
>  uvc_video_start_streaming+0x91/0xdd [uvcvideo]
>  uvc_start_streaming+0x28/0x5d [uvcvideo]
>  vb2_start_streaming+0x61/0x143 [videobuf2_common]
>  vb2_core_streamon+0xf7/0x10f [videobuf2_common]
>  uvc_queue_streamon+0x2e/0x41 [uvcvideo]
>  uvc_ioctl_streamon+0x42/0x5c [uvcvideo]
>  __video_do_ioctl+0x33d/0x42a
>  video_usercopy+0x34e/0x5ff
>  ? video_ioctl2+0x16/0x16
>  v4l2_ioctl+0x46/0x53
>  do_vfs_ioctl+0x50a/0x76f
>  ksys_ioctl+0x58/0x83
>  __x64_sys_ioctl+0x1a/0x1e
>  do_syscall_64+0x54/0xde
> 
> usb_set_interface() should not be called after the USB device has been
> unregistered. However, in the above case the disconnect happened after
> v4l2_ioctl() was called, but before the call to usb_ifnum_to_if().
> 
> Acquire various mutexes in uvc_unregister_video() to fix the majority
> (maybe all) of the observed race conditions.
> 
> The uvc_device lock prevents races against suspend and resume calls
> and the poll function.
> 
> The uvc_streaming lock prevents races against stream related functions;
> for the most part, those are ioctls. This lock also requires other
> functions using this lock to check if a video device is still registered
> after acquiring it. For example, it was observed that the video device
> was already unregistered by the time the stream lock was acquired in
> uvc_ioctl_streamon().
> 
> The uvc_queue lock prevents races against queue functions, Most of
> those are already protected by the uvc_streaming lock, but some
> are called directly. This is done as added protection; an actual race
> was not (yet) observed.
> 
> Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> Reviewed-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 413c32867617..3408b865d346 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1907,14 +1907,22 @@ static void uvc_unregister_video(struct uvc_device *dev)
>  {
>  	struct uvc_streaming *stream;
>  
> +	mutex_lock(&dev->lock);
> +
>  	list_for_each_entry(stream, &dev->streams, list) {
>  		if (!video_is_registered(&stream->vdev))
>  			continue;
>  
> +		mutex_lock(&stream->mutex);
> +		mutex_lock(&stream->queue.mutex);
> +
>  		video_unregister_device(&stream->vdev);
>  		video_unregister_device(&stream->meta.vdev);
>  
>  		uvc_debugfs_cleanup_stream(stream);
> +
> +		mutex_unlock(&stream->queue.mutex);
> +		mutex_unlock(&stream->mutex);
>  	}
>  
>  	uvc_status_unregister(dev);
> @@ -1925,6 +1933,7 @@ static void uvc_unregister_video(struct uvc_device *dev)
>  	if (media_devnode_is_registered(dev->mdev.devnode))
>  		media_device_unregister(&dev->mdev);
>  #endif
> +	mutex_unlock(&dev->lock);
>  }
>  
>  int uvc_register_video_device(struct uvc_device *dev,
> 

Instead of acquiring all the possible locks, could you instead take the
same approach as you do with ISP? It should use refcount_t btw.
<URL:https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/heads/kcam-6.1/drivers/isp/isp-device.c:

-- 
Regards,

Sakari Ailus