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

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 <redacted>
Signed-off-by: Stefan Hajnoczi <stefanha@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

On Thu, Aug 04, 2016 at 02:52:53PM +0100, Stefan Hajnoczi wrote:

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 <redacted>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Thanks!
I'd prefer a lower-case prefix, mentioning vhost, such as vhost/vsock.
I'll tweak it for now.

On Thu, Aug 04, 2016 at 07:34:43PM +0300, Michael S. Tsirkin wrote:

On Thu, Aug 04, 2016 at 02:52:53PM +0100, Stefan Hajnoczi wrote:

quoted

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 <redacted>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Thanks!
I'd prefer a lower-case prefix, mentioning vhost, such as vhost/vsock.
I'll tweak it for now.

Thanks, I will use vhost/vsock in the future.

Stefan