Commit e0bc2c24 authored Nov 11, 2015 by Daniel Borkmann Committed by Sasha Levin Dec 14, 2015

packet: infer protocol from ethernet header if unset



[ Upstream commit c72219b75fde768efccf7666342282fab7f9e4e7 ]

In case no struct sockaddr_ll has been passed to packet
socket's sendmsg() when doing a TX_RING flush run, then
skb->protocol is set to po->num instead, which is the protocol
passed via socket(2)/bind(2).

Applications only xmitting can go the path of allocating the
socket as socket(PF_PACKET, <mode>, 0) and do a bind(2) on the
TX_RING with sll_protocol of 0. That way, register_prot_hook()
is neither called on creation nor on bind time, which saves
cycles when there's no interest in capturing anyway.

That leaves us however with po->num 0 instead and therefore
the TX_RING flush run sets skb->protocol to 0 as well. Eric
reported that this leads to problems when using tools like
trafgen over bonding device. I.e. the bonding's hash function
could invoke the kernel's flow dissector, which depends on
skb->protocol being properly set. In the current situation, all
the traffic is then directed to a single slave.

Fix it up by inferring skb->protocol from the Ethernet header
when not set and we have ARPHRD_ETHER device type. This is only
done in case of SOCK_RAW and where we have a dev->hard_header_len
length. In case of ARPHRD_ETHER devices, this is guaranteed to
cover ETH_HLEN, and therefore being accessed on the skb after
the skb_store_bits().

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent 9293664a

net/packet/af_packet.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -2087,6 +2087,15 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
		sock_wfree(skb);
		}

		static void tpacket_set_protocol(const struct net_device *dev,
		struct sk_buff *skb)
		{
		if (dev->type == ARPHRD_ETHER) {
		skb_reset_mac_header(skb);
		skb->protocol = eth_hdr(skb)->h_proto;
		}
		}

		static int tpacket_fill_skb(struct packet_sock po, struct sk_buff skb,
		void frame, struct net_device dev, int size_max,
		__be16 proto, unsigned char *addr, int hlen)
		@@ -2172,6 +2181,8 @@ static int tpacket_fill_skb(struct packet_sock po, struct sk_buff skb,
		dev->hard_header_len);
		if (unlikely(err))
		return err;
		if (!skb->protocol)
		tpacket_set_protocol(dev, skb);

		data += dev->hard_header_len;
		to_write -= dev->hard_header_len;