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Subject[PATCH 4.9 65/66] vhost: fix vhost_vq_access_ok() log check
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Hajnoczi <stefanha@redhat.com>


[ Upstream commit d14d2b78090c7de0557362b26a4ca591aa6a9faa ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/vhost/vhost.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1175,10 +1175,12 @@ static int vq_log_access_ok(struct vhost
/* 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);
}

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