[PATCH 4.9 070/105] packet: only test po->has_vnet_hdr once in packet_snd

[Greg Kroah-Hartman]

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

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

From: Willem de Bruijn <willemb@xxxxxxxxxx>


[ Upstream commit da7c9561015e93d10fe6aab73e9288e0d09d65a6 ]

Packet socket option po->has_vnet_hdr can be updated concurrently with
other operations if no ring is attached.

Do not test the option twice in packet_snd, as the value may change in
between calls. A race on setsockopt disable may cause a packet > mtu
to be sent without having GSO options set.

Fixes: bfd5f4a3d605 ("packet: Add GSO/csum offload support.")
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/packet/af_packet.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1713,7 +1713,7 @@ static int fanout_add(struct sock *sk, u
 	}
 	spin_unlock(&po->bind_lock);
 
-	if (err && !refcount_read(&match->sk_ref)) {
+	if (err && !atomic_read(&match->sk_ref)) {
 		list_del(&match->list);
 		kfree(match);
 	}
@@ -2838,6 +2838,7 @@ static int packet_snd(struct socket *soc
 	struct virtio_net_hdr vnet_hdr = { 0 };
 	int offset = 0;
 	struct packet_sock *po = pkt_sk(sk);
+	bool has_vnet_hdr = false;
 	int hlen, tlen, linear;
 	int extra_len = 0;
 
@@ -2881,6 +2882,7 @@ static int packet_snd(struct socket *soc
 		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr);
 		if (err)
 			goto out_unlock;
+		has_vnet_hdr = true;
 	}
 
 	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {
@@ -2941,7 +2943,7 @@ static int packet_snd(struct socket *soc
 
 	packet_pick_tx_queue(dev, skb);
 
-	if (po->has_vnet_hdr) {
+	if (has_vnet_hdr) {
 		err = packet_snd_vnet_gso(skb, &vnet_hdr);
 		if (err)
 			goto out_free;