[PATCH] VSOCK: fix vhost virtio_vsock_pkt use-after-free

[Stefan Hajnoczi]

Stash the packet length in a local variable before handing over
ownership of the packet to virtio_transport_recv_pkt() or
virtio_transport_free_pkt().

This patch solves the use-after-free since pkt is no longer guaranteed
to be alive.

Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
 drivers/vhost/vsock.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 0ddf3a2..e3b30ea 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -307,6 +307,8 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work 
*work)
 
        vhost_disable_notify(&vsock->dev, vq);
        for (;;) {
+               u32 len;
+
                if (!vhost_vsock_more_replies(vsock)) {
                        /* Stop tx until the device processes already
                         * pending replies.  Leave tx virtqueue
@@ -334,13 +336,15 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work 
*work)
                        continue;
                }
 
+               len = pkt->len;
+
                /* Only accept correctly addressed packets */
                if (le64_to_cpu(pkt->hdr.src_cid) == vsock->guest_cid)
                        virtio_transport_recv_pkt(pkt);
                else
                        virtio_transport_free_pkt(pkt);
 
-               vhost_add_used(vq, head, sizeof(pkt->hdr) + pkt->len);
+               vhost_add_used(vq, head, sizeof(pkt->hdr) + len);
                added = true;
        }
 
-- 
2.7.4