[PATCH v3 1/2] vhost: fix vhost_vq_access_ok() log check

From: Stefan Hajnoczi
Date: Tue Apr 10 2018 - 22:36:03 EST


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@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
drivers/vhost/vhost.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index bec722e41f58..fc805b7fad9d 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);
}
--
2.14.3