Patch "packet: infer protocol from ethernet header if unset" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

packet: infer protocol from ethernet header if unset

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
packet-infer-protocol-from-ethernet-header-if-unset.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Borkmann <[email protected]>
Date: Wed, 11 Nov 2015 23:25:43 +0100
Subject: packet: infer protocol from ethernet header if unset

From: Daniel Borkmann <[email protected]>

[ 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().

---
 net/packet/af_packet.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

@@ -2121,6 +2121,15 @@ static bool ll_header_truncated(const st
 	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)

@@ -2202,6 +2211,8 @@ static int tpacket_fill_skb(struct packe
 				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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/packet-infer-protocol-from-ethernet-header-if-unset.patch queue-4.1/bpf-array-fix-heap-out-of-bounds-access-when-updating-elements.patch queue-4.1/ipv6-sctp-implement-sctp_v6_destroy_sock.patch queue-4.1/packet-only-allow-extra-vlan-len-on-ethernet-devices.patch queue-4.1/net-scm-fix-pax-detected-msg_controllen-overflow-in-scm_detach_fds.patch queue-4.1/packet-fix-tpacket_snd-max-frame-len.patch queue-4.1/packet-always-probe-for-transport-header.patch queue-4.1/packet-do-skb_probe_transport_header-when-we-actually-have-data.patch queue-4.1/tools-net-use-include-uapi-with-__exported_headers__.patch