[PATCH 4.9 23/77] 9p/trans_virtio: discard zero-length reply

From: Greg Kroah-Hartman
Date: Wed Feb 21 2018 - 07:55:03 EST


4.9-stable review patch. If anyone has any objections, please let me know.

------------------

From: Greg Kurz <groug@xxxxxxxx>

commit 26d99834f89e76514076d9cd06f61e56e6a509b8 upstream.

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@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kurz <groug@xxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
net/9p/trans_virtio.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -160,7 +160,8 @@ static void req_done(struct virtqueue *v
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);
}
}