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

[Willem de Bruijn]

From: Willem de Bruijn <will...@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 <will...@google.com>
Reviewed-by: Eric Dumazet <eduma...@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