V4L/DVB (13831): uvcvideo: Fix oops caused by a race condition in buffer dequeuing

Buffers were marked as done before being removed from the IRQ queue. If
a userspace application dequeued and requeued the buffer fast enough
during that time window, the buffer could end up being deleted twice,
generating an oops in interrupt context.

Add a new state, UVC_BUF_STATE_READY, to mark buffers as ready for reuse
but not yet removed from the queue, and transition to UVC_BUF_STATE_DONE
only when the buffer is removed from the queue.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_queue.c

@@ -59,9 +59,9 @@
  *    returns immediately.
  *
  *    When the buffer is full, the completion handler removes it from the irq
- *    queue, marks it as ready (UVC_BUF_STATE_DONE) and wakes its wait queue.
+ *    queue, marks it as done (UVC_BUF_STATE_DONE) and wakes its wait queue.
  *    At that point, any process waiting on the buffer will be woken up. If a
- *    process tries to dequeue a buffer after it has been marked ready, the
+ *    process tries to dequeue a buffer after it has been marked done, the
  *    dequeing will succeed immediately.
  *
  * 2. Buffers are queued, user is waiting on a buffer and the device gets
@@ -201,6 +201,7 @@ static void __uvc_query_buffer(struct uvc_buffer *buf,
 		break;
 	case UVC_BUF_STATE_QUEUED:
 	case UVC_BUF_STATE_ACTIVE:
+	case UVC_BUF_STATE_READY:
 		v4l2_buf->flags |= V4L2_BUF_FLAG_QUEUED;
 		break;
 	case UVC_BUF_STATE_IDLE:
@@ -295,13 +296,15 @@ static int uvc_queue_waiton(struct uvc_buffer *buf, int nonblocking)
 {
 	if (nonblocking) {
 		return (buf->state != UVC_BUF_STATE_QUEUED &&
-			buf->state != UVC_BUF_STATE_ACTIVE)
+			buf->state != UVC_BUF_STATE_ACTIVE &&
+			buf->state != UVC_BUF_STATE_READY)
 			? 0 : -EAGAIN;
 	}
 
 	return wait_event_interruptible(buf->wait,
 		buf->state != UVC_BUF_STATE_QUEUED &&
-		buf->state != UVC_BUF_STATE_ACTIVE);
+		buf->state != UVC_BUF_STATE_ACTIVE &&
+		buf->state != UVC_BUF_STATE_READY);
 }
 
 /*
@@ -348,6 +351,7 @@ int uvc_dequeue_buffer(struct uvc_video_queue *queue,
 	case UVC_BUF_STATE_IDLE:
 	case UVC_BUF_STATE_QUEUED:
 	case UVC_BUF_STATE_ACTIVE:
+	case UVC_BUF_STATE_READY:
 	default:
 		uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state %u "
 			"(driver bug?).\n", buf->state);
@@ -489,6 +493,7 @@ struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
 
 	spin_lock_irqsave(&queue->irqlock, flags);
 	list_del(&buf->queue);
+	buf->state = UVC_BUF_STATE_DONE;
 	if (!list_empty(&queue->irqqueue))
 		nextbuf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
 					   queue);

drivers/media/video/uvc/uvc_video.c

@@ -441,7 +441,7 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 	if (fid != stream->last_fid && buf->buf.bytesused != 0) {
 		uvc_trace(UVC_TRACE_FRAME, "Frame complete (FID bit "
 				"toggled).\n");
-		buf->state = UVC_BUF_STATE_DONE;
+		buf->state = UVC_BUF_STATE_READY;
 		return -EAGAIN;
 	}
 
@@ -470,7 +470,7 @@ static void uvc_video_decode_data(struct uvc_streaming *stream,
 	/* Complete the current frame if the buffer size was exceeded. */
 	if (len > maxlen) {
 		uvc_trace(UVC_TRACE_FRAME, "Frame complete (overflow).\n");
-		buf->state = UVC_BUF_STATE_DONE;
+		buf->state = UVC_BUF_STATE_READY;
 	}
 }
 
@@ -482,7 +482,7 @@ static void uvc_video_decode_end(struct uvc_streaming *stream,
 		uvc_trace(UVC_TRACE_FRAME, "Frame complete (EOF found).\n");
 		if (data[0] == len)
 			uvc_trace(UVC_TRACE_FRAME, "EOF in empty payload.\n");
-		buf->state = UVC_BUF_STATE_DONE;
+		buf->state = UVC_BUF_STATE_READY;
 		if (stream->dev->quirks & UVC_QUIRK_STREAM_NO_FID)
 			stream->last_fid ^= UVC_STREAM_FID;
 	}
@@ -568,8 +568,7 @@ static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
 		uvc_video_decode_end(stream, buf, mem,
 			urb->iso_frame_desc[i].actual_length);
 
-		if (buf->state == UVC_BUF_STATE_DONE ||
-		    buf->state == UVC_BUF_STATE_ERROR)
+		if (buf->state == UVC_BUF_STATE_READY)
 			buf = uvc_queue_next_buffer(&stream->queue, buf);
 	}
 }
@@ -627,8 +626,7 @@ static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
 		if (!stream->bulk.skip_payload && buf != NULL) {
 			uvc_video_decode_end(stream, buf, stream->bulk.header,
 				stream->bulk.payload_size);
-			if (buf->state == UVC_BUF_STATE_DONE ||
-			    buf->state == UVC_BUF_STATE_ERROR)
+			if (buf->state == UVC_BUF_STATE_READY)
 				buf = uvc_queue_next_buffer(&stream->queue,
 							    buf);
 		}
@@ -669,7 +667,7 @@ static void uvc_video_encode_bulk(struct urb *urb, struct uvc_streaming *stream,
 	    stream->bulk.payload_size == stream->bulk.max_payload_size) {
 		if (buf->buf.bytesused == stream->queue.buf_used) {
 			stream->queue.buf_used = 0;
-			buf->state = UVC_BUF_STATE_DONE;
+			buf->state = UVC_BUF_STATE_READY;
 			uvc_queue_next_buffer(&stream->queue, buf);
 			stream->last_fid ^= UVC_STREAM_FID;
 		}

drivers/media/video/uvc/uvcvideo.h

@@ -365,8 +365,9 @@ enum uvc_buffer_state {
 	UVC_BUF_STATE_IDLE	= 0,
 	UVC_BUF_STATE_QUEUED	= 1,
 	UVC_BUF_STATE_ACTIVE	= 2,
-	UVC_BUF_STATE_DONE	= 3,
-	UVC_BUF_STATE_ERROR	= 4,
+	UVC_BUF_STATE_READY	= 3,
+	UVC_BUF_STATE_DONE	= 4,
+	UVC_BUF_STATE_ERROR	= 5,
 };
 
 struct uvc_buffer {