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Thu, 03 Sep 2026 06:12:24 -0700 (PDT) From: huhb1 X-Google-Original-From: huhb1 To: laurent.pinchart@ideasonboard.com, hansg@kernel.org Cc: mchehab@kernel.org, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, huhb04 , stable@vger.kernel.org Subject: [PATCH] media: uvcvideo: defer cancelled buffer completion until copies finish Date: Thu, 3 Sep 2026 21:11:41 +0800 Message-Id: <20260903131141.6368-1-huhb1@xiaopeng.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: huhb04 uvc_queue_cancel() returns queued buffers to videobuf2 directly via vb2_buffer_done(). This is unsafe because asynchronous memcpy workers may still hold a reference on the same uvc_buffer. Once vb2_buffer_done() has run, userspace can dequeue and requeue the buffer while the old worker is still running, leading to the same list_head being inserted into irqqueue twice and corrupting the list. The crash manifests in two ways depending on the drop-corrupted-frames module parameter: 1. With the drop corrupted frames enabled, the old worker's final kref_put reaches uvc_queue_buffer_complete(), sees buf->error set, and calls uvc_queue_buffer_requeue(). This performs list_add_tail() on buf->queue even though userspace has already QBUF'd the same buffer and added it to irqqueue. 2. With nodrop=1, uvc_queue_buffer_complete() calls vb2_buffer_done() a second time. If userspace has already dequeued and requeued the buffer, the second completion exposes it to userspace again, and the next DQBUF/QBUF inserts the still-linked list_head into irqqueue a second time. Both cases produce the kind of list_del corruption seen here: list_del corruption. next->prev should be ..., but was ... kernel BUG at lib/list_debug.c:64! Fix the cancel path to remove buffers from irqqueue and drop the queue's reference through uvc_queue_buffer_release() (i.e. kref_put()). The final VB2 completion then only happens from uvc_queue_buffer_complete() once the last async reference is released, so userspace cannot reuse the buffer while an old worker still accesses it. A buffer whose state is already UVC_BUF_STATE_ERROR is forced to complete as an error and must not be requeued by the corrupted-frame policy. Normal malformed frames are still requeued/dropped as before. Fixes: 01e90464e42e ("media: uvcvideo: queue: Support asynchronous buffer handling") Cc: stable@vger.kernel.org Signed-off-by: huhb04 --- drivers/media/usb/uvc/uvc_queue.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c index 3c002c8f44..9206e0a355 100644 --- a/drivers/media/usb/uvc/uvc_queue.c +++ b/drivers/media/usb/uvc/uvc_queue.c @@ -289,10 +289,19 @@ int uvc_queue_init(struct uvc_streaming *stream, struct uvc_video_queue *queue, */ void uvc_queue_cancel(struct uvc_video_queue *queue, int disconnect) { + struct uvc_buffer *buf, *next; + struct list_head local_list; unsigned long flags; + INIT_LIST_HEAD(&local_list); + spin_lock_irqsave(&queue->irqlock, flags); - __uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR); + while (!list_empty(&queue->irqqueue)) { + buf = list_first_entry(&queue->irqqueue, struct uvc_buffer, queue); + list_del(&buf->queue); + buf->state = UVC_BUF_STATE_ERROR; + list_add_tail(&buf->queue, &local_list); + } /* * This must be protected by the irqlock spinlock to avoid race * conditions between uvc_buffer_queue and the disconnection event that @@ -303,6 +312,17 @@ void uvc_queue_cancel(struct uvc_video_queue *queue, int disconnect) if (disconnect) queue->flags |= UVC_QUEUE_DISCONNECTED; spin_unlock_irqrestore(&queue->irqlock, flags); + + /* + * Release the queue-owned kref outside the irqlock. The final VB2 + * completion only happens from uvc_queue_buffer_complete() once all + * asynchronous copy references have been released, preventing userspace + * from reusing the buffer while an old worker still accesses it. + */ + list_for_each_entry_safe(buf, next, &local_list, queue) { + list_del(&buf->queue); + uvc_queue_buffer_release(buf); + } } /* @@ -356,7 +376,13 @@ static void uvc_queue_buffer_complete(struct kref *ref) struct vb2_buffer *vb = &buf->buf.vb2_buf; struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue); - if (buf->error && !uvc_no_drop_param) { + /* + * Buffers cancelled from uvc_queue_cancel() are forced to complete as + * errors. They must not be requeued by the corrupted-frame policy even + * when buf->error is set. + */ + if (buf->state != UVC_BUF_STATE_ERROR && + buf->error && !uvc_no_drop_param) { uvc_queue_buffer_requeue(queue, buf); return; } -- 2.34.1