[PATCH net] vrf: Fix use after free and double free in vrf_finish_output

[David Ahern <dsahern@gmail.com>]

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@teldat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
---
 drivers/net/vrf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 139c61c8244a..ac40924fe437 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -578,12 +578,13 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
 	if (!IS_ERR(neigh)) {
 		sock_confirm_neigh(skb, neigh);
 		ret = neigh_output(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;
 }
 
-- 
2.11.0