Commit 9382fe71 authored Jan 31, 2018 by Ed Swierk Committed by David S. Miller Feb 01, 2018

openvswitch: Remove padding from packet before L3+ conntrack processing



IPv4 and IPv6 packets may arrive with lower-layer padding that is not
included in the L3 length. For example, a short IPv4 packet may have
up to 6 bytes of padding following the IP payload when received on an
Ethernet device with a minimum packet length of 64 bytes.

Higher-layer processing functions in netfilter (e.g. nf_ip_checksum(),
and help() in nf_conntrack_ftp) assume skb->len reflects the length of
the L3 header and payload, rather than referring back to
ip_hdr->tot_len or ipv6_hdr->payload_len, and get confused by
lower-layer padding.

In the normal IPv4 receive path, ip_rcv() trims the packet to
ip_hdr->tot_len before invoking netfilter hooks. In the IPv6 receive
path, ip6_rcv() does the same using ipv6_hdr->payload_len. Similarly
in the br_netfilter receive path, br_validate_ipv4() and
br_validate_ipv6() trim the packet to the L3 length before invoking
netfilter hooks.

Currently in the OVS conntrack receive path, ovs_ct_execute() pulls
the skb to the L3 header but does not trim it to the L3 length before
calling nf_conntrack_in(NF_INET_PRE_ROUTING). When
nf_conntrack_proto_tcp encounters a packet with lower-layer padding,
nf_ip_checksum() fails causing a "nf_ct_tcp: bad TCP checksum" log
message. While extra zero bytes don't affect the checksum, the length
in the IP pseudoheader does. That length is based on skb->len, and
without trimming, it doesn't match the length the sender used when
computing the checksum.

In ovs_ct_execute(), trim the skb to the L3 length before higher-layer
processing.

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 3aff3b4b

net/openvswitch/conntrack.c

+34 −0

Original line number	Original line	Diff line number	Diff line
	@@ -1098,6 +1098,36 @@ static int ovs_ct_commit(struct net net, struct sw_flow_key key,
	return 0;		return 0;
	}		}

			/* Trim the skb to the length specified by the IP/IPv6 header,
			* removing any trailing lower-layer padding. This prepares the skb
			* for higher-layer processing that assumes skb->len excludes padding
			* (such as nf_ip_checksum). The caller needs to pull the skb to the
			* network header, and ensure ip_hdr/ipv6_hdr points to valid data.
			*/
			static int ovs_skb_network_trim(struct sk_buff *skb)
			{
			unsigned int len;
			int err;

			switch (skb->protocol) {
			case htons(ETH_P_IP):
			len = ntohs(ip_hdr(skb)->tot_len);
			break;
			case htons(ETH_P_IPV6):
			len = sizeof(struct ipv6hdr)
			+ ntohs(ipv6_hdr(skb)->payload_len);
			break;
			default:
			len = skb->len;
			}

			err = pskb_trim_rcsum(skb, len);
			if (err)
			kfree_skb(skb);

			return err;
			}

	/* Returns 0 on success, -EINPROGRESS if 'skb' is stolen, or other nonzero		/* Returns 0 on success, -EINPROGRESS if 'skb' is stolen, or other nonzero
	* value if 'skb' is freed.		* value if 'skb' is freed.
	*/		*/
	@@ -1112,6 +1142,10 @@ int ovs_ct_execute(struct net net, struct sk_buff skb,
	nh_ofs = skb_network_offset(skb);		nh_ofs = skb_network_offset(skb);
	skb_pull_rcsum(skb, nh_ofs);		skb_pull_rcsum(skb, nh_ofs);

			err = ovs_skb_network_trim(skb);
			if (err)
			return err;

	if (key->ip.frag != OVS_FRAG_TYPE_NONE) {		if (key->ip.frag != OVS_FRAG_TYPE_NONE) {
	err = handle_fragments(net, key, info->zone.id, skb);		err = handle_fragments(net, key, info->zone.id, skb);
	if (err)		if (err)

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