linux-kernel - [PATCH 4.9 075/329] openvswitch: Remove padding from packet before L3+ conntrack processing

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Message-Id: <20180528100249.088945809@linuxfoundation.org>
Date:   Mon, 28 May 2018 12:00:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ed Swierk <eswierk@...portsystems.com>,
        Pravin B Shelar <pshelar@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.9 075/329] openvswitch: Remove padding from packet before L3+ conntrack processing

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ed Swierk <eswierk@...portsystems.com>

[ Upstream commit 9382fe71c0058465e942a633869629929102843d ]

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@...portsystems.com>
Acked-by: Pravin B Shelar <pshelar@....org>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/openvswitch/conntrack.c |   34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -906,6 +906,36 @@ static int ovs_ct_commit(struct net *net
 	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
  * value if 'skb' is freed.
  */
@@ -920,6 +950,10 @@ int ovs_ct_execute(struct net *net, stru
 	nh_ofs = skb_network_offset(skb);
 	skb_pull_rcsum(skb, nh_ofs);

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