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From:   Stefan Hajnoczi <stefanha@redhat.com>
To:     virtualization@lists.linux-foundation.org
Cc:     linux-kernel@vger.kernel.org, jasowang@redhat.com,
        kvm@vger.kernel.org, mst@redhat.com,
        syzkaller-bugs@googlegroups.com,
        Stefan Hajnoczi <stefanha@redhat.com>
Subject: [PATCH] vhost: fix vhost_vq_access_ok() log check
Date:   Mon,  9 Apr 2018 21:10:21 +0800
Message-Id: <20180409131021.5132-1-stefanha@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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;

The correct logic is:

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

Reported-by: syzbot+65a84dde0214b0387ccd@syzkaller.appspotmail.com
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 drivers/vhost/vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 5320039671b7..f6af4210679a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1246,7 +1246,7 @@ int vhost_vq_access_ok(struct vhost_virtqueue *vq)
 {
 	int ret = vq_log_access_ok(vq, vq->log_base);
 
-	if (ret || vq->iotlb)
+	if (!ret || vq->iotlb)
 		return ret;
 
 	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
-- 
2.14.3