packet: only test po->has_vnet_hdr once in packet_snd

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@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2d44726..4f6392d 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2231,6 +2231,7 @@ static int packet_snd(struct socket *sock,
        int offset = 0;
        int vnet_hdr_len;
        struct packet_sock *po = pkt_sk(sk);
+       bool has_vnet_hdr = false;
        unsigned short gso_type = 0;
 
        /*
@@ -2263,6 +2264,7 @@ static int packet_snd(struct socket *sock,
                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)
@@ -2354,7 +2356,7 @@ static int packet_snd(struct socket *sock,
        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)) {