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    Subject[PATCH 4.15 141/163] 9p/trans_virtio: discard zero-length reply
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

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

    From: Greg Kurz <groug@kaod.org>

    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@vger.kernel.org
    Signed-off-by: Greg Kurz <groug@kaod.org>
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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);
    }
    }


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