packet: round up linear to header len

[ Upstream commit 57031eb794906eea4e1c7b31dc1e2429c0af0c66 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 94e4a5941d89..458722b938c7 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2813,7 +2813,7 @@ 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;
 
         /*
@@ -2874,8 +2874,9 @@ 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;