vringh: fix __vringh_iov() when riov and wiov are different

commit 5745bcfbbf89b158416075374254d3c013488f21 upstream.

If riov and wiov are both defined and they point to different
objects, only riov is initialized. If the wiov is not initialized
by the caller, the function fails returning -EINVAL and printing
"Readable desc 0x... after writable" error message.

This issue happens when descriptors have both readable and writable
buffers (eg. virtio-blk devices has virtio_blk_outhdr in the readable
buffer and status as last byte of writable buffer) and we call
__vringh_iov() to get both type of buffers in two different iovecs.

Let's replace the 'else if' clause with 'if' to initialize both
riov and wiov if they are not NULL.

As checkpatch pointed out, we also avoid crashing the kernel
when riov and wiov are both NULL, replacing BUG() with WARN_ON()
and returning -EINVAL.

Fixes: f87d0fbb5798 ("vringh: host-side implementation of virtio rings.")
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20201008204256.162292-1-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 3bb02c60a2f5fe85a4d38e5d884b66f03b8756e9..d56736655dec4dfa4c29d54bcd950eaf1e25a4cf 100644 (file)
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -272,13 +272,14 @@ __vringh_iov(struct vringh *vrh, u16 i,
        desc_max = vrh->vring.num;
        up_next = -1;
 
+       /* You must want something! */
+       if (WARN_ON(!riov && !wiov))
+               return -EINVAL;
+
        if (riov)
                riov->i = riov->used = 0;
-       else if (wiov)
+       if (wiov)
                wiov->i = wiov->used = 0;
-       else
-               /* You must want something! */
-               BUG();
 
        for (;;) {
                void *addr;