9p: virtio: fix unlikely null pointer deref in handle_rerror

handle_rerror can dereference the pages pointer, but it is not
necessarily set for small payloads.
In practice these should be filtered out by the size check, but
might as well double-check explicitly.

This fixes the following scan-build warnings:
net/9p/trans_virtio.c:401:24: warning: Dereference of null pointer [core.NullDereference]
                memcpy_from_page(to, *pages++, offs, n);
                                     ^~~~~~~~
net/9p/trans_virtio.c:406:23: warning: Dereference of null pointer (loaded from variable 'pages') [core.NullDereference]
        memcpy_from_page(to, *pages, offs, size);
                             ^~~~~~

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3c27ffb781e3e03f05e13e45c23c61af29d617b9..2c9495ccda6baa2a594e9b79007bb705564bb8e6 100644 (file)
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -384,7 +384,7 @@ static void handle_rerror(struct p9_req_t *req, int in_hdr_len,
        void *to = req->rc.sdata + in_hdr_len;
 
        // Fits entirely into the static data?  Nothing to do.
-       if (req->rc.size < in_hdr_len)
+       if (req->rc.size < in_hdr_len || !pages)
                return;
 
        // Really long error message?  Tough, truncate the reply.  Might get