[PATCH 4.4 17/46] packet: only test po->has_vnet_hdr once in packet_snd

[Greg Kroah-Hartman]

4.4-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
@@ -1717,7 +1717,7 @@ 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);
 	}
@@ -2656,6 +2656,7 @@ static int packet_snd(struct socket *soc
 	int vnet_hdr_len;
 	struct packet_sock *po = pkt_sk(sk);
 	unsigned short gso_type = 0;
+	bool has_vnet_hdr = false;
 	int hlen, tlen, linear;
 	int extra_len = 0;
 	ssize_t n;
@@ -2743,6 +2744,7 @@ static int packet_snd(struct socket *soc
 				goto out_unlock;
 
 		}
+		has_vnet_hdr = true;
 	}
 
 	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {
@@ -2802,7 +2804,7 @@ static int packet_snd(struct socket *soc
 
 	packet_pick_tx_queue(dev, skb);
 
-	if (po->has_vnet_hdr) {
+	if (has_vnet_hdr) {
 		if (vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
 			u16 s = __virtio16_to_cpu(vio_le(), vnet_hdr.csum_start);
 			u16 o = __virtio16_to_cpu(vio_le(), vnet_hdr.csum_offset);