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SubjectRe: [PATCH 0/5] media: uvcvideo: Fix race conditions
Hi Guenter,

Thank you for the patches.

On Sun, Aug 30, 2020 at 08:04:38AM -0700, Guenter Roeck wrote:
> The uvcvideo code has no lock protection against USB disconnects
> while video operations are ongoing. This has resulted in random
> error reports, typically pointing to a crash in usb_ifnum_to_if(),
> called from usb_hcd_alloc_bandwidth(). A typical traceback is as
> follows.
>
> 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
>
> While this is problem rarely observed in the field, it is relatively easy
> to reproduce by adding msleep() calls into the code.
>
> I don't presume to claim that I found every issue, but this patch series
> should fix at least the major problems.
>
> The patch series was tested exensively on a Chromebook running chromeos-4.19
> and on a Linux system running a v5.8.y based kernel.

I'll review each patch individually, but I think 2/5, 4/5 and 5/5 should
be handled in the V4L2 core, not the uvcvideo driver. Otherwise we would
have to replicate that logic in all drivers, while I think it can easily
be implemented in a generic fashion as previously discussed.

> ----------------------------------------------------------------
> Guenter Roeck (5):
> media: uvcvideo: Cancel async worker earlier
> media: uvcvideo: Lock video streams and queues while unregistering
> media: uvcvideo: Release stream queue when unregistering video device
> media: uvcvideo: Protect uvc queue file operations against disconnect
> media: uvcvideo: In uvc_v4l2_open, check if video device is registered
>
> drivers/media/usb/uvc/uvc_ctrl.c | 11 ++++++----
> drivers/media/usb/uvc/uvc_driver.c | 12 ++++++++++
> drivers/media/usb/uvc/uvc_queue.c | 32 +++++++++++++++++++++++++--
> drivers/media/usb/uvc/uvc_v4l2.c | 45 ++++++++++++++++++++++++++++++++++++--
> drivers/media/usb/uvc/uvcvideo.h | 1 +
> 5 files changed, 93 insertions(+), 8 deletions(-)

--
Regards,

Laurent Pinchart

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