vhost: fix vhost_vq_access_ok() log check

Commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ("vhost: validate log
when IOTLB is enabled") introduced a regression.  The logic was
originally:

  if (vq->iotlb)
      return 1;
  return A && B;

After the patch the short-circuit logic for A was inverted:

  if (A || vq->iotlb)
      return A;
  return B;

This patch fixes the regression by rewriting the checks in the obvious
way, no longer returning A when vq->iotlb is non-NULL (which is hard to
understand).

Reported-by: syzbot+65a84dde0214b0387ccd@syzkaller.appspotmail.com
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f44aead98d60..9a18535fafba 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1244,10 +1244,12 @@ static int vq_log_access_ok(struct vhost_virtqueue *vq,
 /* Caller should have vq mutex and device mutex */
 int vhost_vq_access_ok(struct vhost_virtqueue *vq)
 {
-        int ret = vq_log_access_ok(vq, vq->log_base);
+        if (!vq_log_access_ok(vq, vq->log_base))
+                return 0;
 
-        if (ret || vq->iotlb)
-                return ret;
+        /* Access validation occurs at prefetch time with IOTLB */
+        if (vq->iotlb)
+                return 1;
 
         return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
 }