9p/trans_virtio: discard zero-length reply

When a 9p request is successfully flushed, the server is expected to just
mark it as used without sending a 9p reply (ie, without writing data into
the buffer). In this case, virtqueue_get_buf() will return len == 0 and
we must not report a REQ_STATUS_RCVD status to the client, otherwise the
client will erroneously assume the request has not been flushed.

Cc: stable@vger.kernel.org
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index f3a4efcf1456..3aa5a93ad107 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -160,7 +160,8 @@ static void req_done(struct virtqueue *vq)
                 spin_unlock_irqrestore(&chan->lock, flags);
                 /* Wakeup if anyone waiting for VirtIO ring space. */
                 wake_up(chan->vc_wq);
-                p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
+                if (len)
+                        p9_client_cb(chan->client, req, REQ_STATUS_RCVD);
         }
 }