9p: BUG before corrupting memory

commit 5fcb08befaf57faa1b00e514915c1660252b8c26 upstream.

The BUG_ON() in pack_sg_list() would get triggered only one time after we've
corrupted some memory by sg_set_buf() into an invalid sg buffer.

I'm still working on figuring out why I manage to trigger that bug...

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 3d43206..052d343 100644 (file)
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -192,10 +192,10 @@ static int pack_sg_list(struct scatterlist *sg, int start,
                s = rest_of_page(data);
                if (s > count)
                        s = count;
+               BUG_ON(index > limit);
                sg_set_buf(&sg[index++], data, s);
                count -= s;
                data += s;
-               BUG_ON(index > limit);
        }
 
        return index-start;