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>

3 files changed, 18 insertions, 14 deletions

diff --git a/drivers/media/video/uvc/uvc_queue.c b/drivers/media/video/uvc/uvc_queue.c
index f854698c4061..ea11839cba4a 100644
--- a/drivers/media/video/uvc/uvc_queue.c
+++ b/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);
diff --git a/drivers/media/video/uvc/uvc_video.c b/drivers/media/video/uvc/uvc_video.c
index e8cc0a9ddadd..7dcf534a0cf3 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;
                 }
diff --git a/drivers/media/video/uvc/uvcvideo.h b/drivers/media/video/uvc/uvcvideo.h
index 7ec9a04ced50..2337585001ea 100644
--- a/drivers/media/video/uvc/uvcvideo.h
+++ b/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 {