[PATCH net] packet: only test po->has_vnet_hdr once in packet_snd

From: Willem de Bruijn <willemb@google.com>

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@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
 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 d288f52c53f7..1da0851f51f2 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c

@@ -2840,6 +2840,7 @@ 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;
 

@@ -2883,6 +2884,7 @@ 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))) {

@@ -2941,7 +2943,7 @@ 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;

-- 
2.14.1.821.g8fa685d3b7-goog

aFrom: Willem de Bruijn [off-list ref]
Date: Tue, 26 Sep 2017 12:20:17 -0400

From: Willem de Bruijn <willemb@google.com>

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@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>

Applied and queued up for -stable.