[PATCH 3.16 071/204] packet: only test po->has_vnet_hdr once in packet_snd

[Ben Hutchings]

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit da7c9561015e93d10fe6aab73e9288e0d09d65a6 upstream.

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>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/packet/af_packet.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2432,6 +2432,7 @@ static int packet_snd(struct socket *soc
 	int offset = 0;
 	int vnet_hdr_len;
 	struct packet_sock *po = pkt_sk(sk);
+	bool has_vnet_hdr = false;
 	unsigned short gso_type = 0;
 	int hlen, tlen;
 	int extra_len = 0;
@@ -2466,6 +2467,7 @@ static int packet_snd(struct socket *soc
 		reserve = dev->hard_header_len;
 	if (po->has_vnet_hdr) {
 		vnet_hdr_len = sizeof(vnet_hdr);
+		has_vnet_hdr = true;
 
 		err = -EINVAL;
 		if (len < vnet_hdr_len)
@@ -2557,7 +2559,7 @@ static int packet_snd(struct socket *soc
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
 
-	if (po->has_vnet_hdr) {
+	if (has_vnet_hdr) {
 		if (vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
 			if (!skb_partial_csum_set(skb, vnet_hdr.csum_start,
 						  vnet_hdr.csum_offset)) {