From c72219b75fde768efccf7666342282fab7f9e4e7 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 11 Nov 2015 23:25:43 +0100 Subject: [PATCH] packet: infer protocol from ethernet header if unset 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, , 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 Signed-off-by: Daniel Borkmann Acked-by: Willem de Bruijn Signed-off-by: David S. Miller --- net/packet/af_packet.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 8795b0fb1ed1..0066da2b8e44 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2338,6 +2338,15 @@ static bool ll_header_truncated(const struct net_device *dev, int len) return false; } +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) @@ -2419,6 +2428,8 @@ 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; -- 2.20.1