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

[Sergey Senozhatsky]

On (23/11/21 19:53), Ricardo Ribalda wrote:
> 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.
> 
[..]
> 
> 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>

Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>