packet: round up linear to header len

Link layer protocols may unconditionally pull headers, as Ethernet
does in eth_type_trans. Ensure that the entire link layer header
always lies in the skb linear segment. tpacket_snd has such a check.
Extend this to packet_snd.

Variable length link layer headers complicate the computation
somewhat. Here skb->len may be smaller than dev->hard_header_len.

Round up the linear length to be at least as long as the smallest of
the two.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 3d555c7..d56ee46 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2755,7 +2755,7 @@ 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);
-       int hlen, tlen;
+       int hlen, tlen, linear;
        int extra_len = 0;
 
        /*
@@ -2816,8 +2816,9 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
        err = -ENOBUFS;
        hlen = LL_RESERVED_SPACE(dev);
        tlen = dev->needed_tailroom;
-       skb = packet_alloc_skb(sk, hlen + tlen, hlen, len,
-                              __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len),
+       linear = __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len);
+       linear = max(linear, min_t(int, len, dev->hard_header_len));
+       skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, linear,
                               msg->msg_flags & MSG_DONTWAIT, &err);
        if (skb == NULL)
                goto out_unlock;