vrf: Fix use after free and double free in vrf_finish_output

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@teldat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ 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@linuxfoundation.org>

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 346e486..42c9480 100644 (file)
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -585,13 +585,15 @@ static int vrf_finish_output(struct net *net, struct sock *sk, struct sk_buff *s
        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;
 }