[PATCH 4.9 310/310] vrf: Fix use after free and double free in vrf_finish_output

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: David Ahern <dsahern@xxxxxxxxx>

commit 82dd0d2a9a76fc8fa2b18d80b987d455728bf83a upstream.

Miguel reported an skb use after free / double free in vrf_finish_output
when neigh_output returns an error. The vrf driver should return after
the call to neigh_output as it takes over the skb on error path as well.

Patch is a simplified version of Miguel's patch which was written for 4.9,
and updated to top of tree.

Fixes: 8f58336d3f78a ("net: Add ethernet header for pass through VRF device")
Signed-off-by: Miguel Fadon Perlines <mfadon@xxxxxxxxxx>
Signed-off-by: David Ahern <dsahern@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[ backport to 4.4 and 4.9 dropped the sock_confirm_neigh and
  changed neigh_output to dst_neigh_output ]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/net/vrf.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -585,13 +585,15 @@ static int vrf_finish_output(struct net
 	neigh = __ipv4_neigh_lookup_noref(dev, nexthop);
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&arp_tbl, &nexthop, dev, false);
-	if (!IS_ERR(neigh))
+	if (!IS_ERR(neigh)) {
 		ret = dst_neigh_output(dst, neigh, skb);
+		rcu_read_unlock_bh();
+		return ret;
+	}
 
 	rcu_read_unlock_bh();
 err:
-	if (unlikely(ret < 0))
-		vrf_tx_error(skb->dev, skb);
+	vrf_tx_error(skb->dev, skb);
 	return ret;
 }