Subject: [PATCH 35/48] packet: only test po->has_vnet_hdr once in packet_snd

From: Willem de Bruijn <[email-masked]>
Date: Tue, 26 Sep 2017 12:20:17 -0400

[ 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 <[email-masked]>
Reviewed-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/packet/af_packet.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 79362d8d3a8e..29d7b7e5b128 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2842,6 +2842,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	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;
 
@@ -2885,6 +2886,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 		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))) {
@@ -2943,7 +2945,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	skb->priority = sk->sk_priority;
 	skb->mark = sockc.mark;
 
-	if (po->has_vnet_hdr) {
+	if (has_vnet_hdr) {
 		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
 		if (err)
 			goto out_free;
-- 
2.13.6