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>

1 files changed, 6 insertions, 8 deletions

diff --git a/drivers/media/video/uvc/uvc_video.c b/drivers/media/video/uvc/uvc_video.c
index e8cc0a9..7dcf534 100644
--- a/drivers/media/video/uvc/uvc_video.c
+++ b/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;
 		}