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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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