1 files changed, 174 insertions, 126 deletions

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index d40f7e4b128..e762de5ee89 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -2,18 +2,23 @@
  * This is a module which is used for setting the MSS option in TCP packets.
  *
  * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
+ * Copyright (C) 2007 Patrick McHardy <kaber@trash.net>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  */
-
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/ip.h>
+#include <linux/gfp.h>
 #include <linux/ipv6.h>
 #include <linux/tcp.h>
+#include <net/dst.h>
+#include <net/flow.h>
 #include <net/ipv6.h>
+#include <net/route.h>
 #include <net/tcp.h>
 
 #include <linux/netfilter_ipv4/ip_tables.h>
@@ -24,7 +29,7 @@
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
-MODULE_DESCRIPTION("x_tables TCP MSS modification module");
+MODULE_DESCRIPTION("Xtables: TCP Maximum Segment Size (MSS) adjustment");
 MODULE_ALIAS("ipt_TCPMSS");
 MODULE_ALIAS("ip6t_TCPMSS");
 
@@ -38,243 +43,286 @@ optlen(const u_int8_t *opt, unsigned int offset)
 		return opt[offset+1];
 }
 
+static u_int32_t tcpmss_reverse_mtu(struct net *net,
+				    const struct sk_buff *skb,
+				    unsigned int family)
+{
+	struct flowi fl;
+	const struct nf_afinfo *ai;
+	struct rtable *rt = NULL;
+	u_int32_t mtu     = ~0U;
+
+	if (family == PF_INET) {
+		struct flowi4 *fl4 = &fl.u.ip4;
+		memset(fl4, 0, sizeof(*fl4));
+		fl4->daddr = ip_hdr(skb)->saddr;
+	} else {
+		struct flowi6 *fl6 = &fl.u.ip6;
+
+		memset(fl6, 0, sizeof(*fl6));
+		fl6->daddr = ipv6_hdr(skb)->saddr;
+	}
+	rcu_read_lock();
+	ai = nf_get_afinfo(family);
+	if (ai != NULL)
+		ai->route(net, (struct dst_entry **)&rt, &fl, false);
+	rcu_read_unlock();
+
+	if (rt != NULL) {
+		mtu = dst_mtu(&rt->dst);
+		dst_release(&rt->dst);
+	}
+	return mtu;
+}
+
 static int
-tcpmss_mangle_packet(struct sk_buff **pskb,
-		     const struct xt_tcpmss_info *info,
+tcpmss_mangle_packet(struct sk_buff *skb,
+		     const struct xt_action_param *par,
+		     unsigned int family,
 		     unsigned int tcphoff,
 		     unsigned int minlen)
 {
+	const struct xt_tcpmss_info *info = par->targinfo;
 	struct tcphdr *tcph;
-	unsigned int tcplen, i;
+	int len, tcp_hdrlen;
+	unsigned int i;
 	__be16 oldval;
 	u16 newmss;
 	u8 *opt;
 
-	if (!skb_make_writable(pskb, (*pskb)->len))
+	/* This is a fragment, no TCP header is available */
+	if (par->fragoff != 0)
+		return 0;
+
+	if (!skb_make_writable(skb, skb->len))
 		return -1;
 
-	tcplen = (*pskb)->len - tcphoff;
-	tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff);
-
-	/* Since it passed flags test in tcp match, we know it is is
-	   not a fragment, and has data >= tcp header length.  SYN
-	   packets should not contain data: if they did, then we risk
-	   running over MTU, sending Frag Needed and breaking things
-	   badly. --RR */
-	if (tcplen != tcph->doff*4) {
-		if (net_ratelimit())
-			printk(KERN_ERR "xt_TCPMSS: bad length (%u bytes)\n",
-			       (*pskb)->len);
+	len = skb->len - tcphoff;
+	if (len < (int)sizeof(struct tcphdr))
+		return -1;
+
+	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
+	tcp_hdrlen = tcph->doff * 4;
+
+	if (len < tcp_hdrlen)
 		return -1;
-	}
 
 	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
-		if (dst_mtu((*pskb)->dst) <= minlen) {
-			if (net_ratelimit())
-				printk(KERN_ERR "xt_TCPMSS: "
-				       "unknown or invalid path-MTU (%u)\n",
-				       dst_mtu((*pskb)->dst));
+		struct net *net = dev_net(par->in ? par->in : par->out);
+		unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family);
+
+		if (dst_mtu(skb_dst(skb)) <= minlen) {
+			net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
+					    dst_mtu(skb_dst(skb)));
 			return -1;
 		}
-		newmss = dst_mtu((*pskb)->dst) - minlen;
+		if (in_mtu <= minlen) {
+			net_err_ratelimited("unknown or invalid path-MTU (%u)\n",
+					    in_mtu);
+			return -1;
+		}
+		newmss = min(dst_mtu(skb_dst(skb)), in_mtu) - minlen;
 	} else
 		newmss = info->mss;
 
 	opt = (u_int8_t *)tcph;
-	for (i = sizeof(struct tcphdr); i < tcph->doff*4; i += optlen(opt, i)) {
-		if (opt[i] == TCPOPT_MSS && tcph->doff*4 - i >= TCPOLEN_MSS &&
-		    opt[i+1] == TCPOLEN_MSS) {
+	for (i = sizeof(struct tcphdr); i <= tcp_hdrlen - TCPOLEN_MSS; i += optlen(opt, i)) {
+		if (opt[i] == TCPOPT_MSS && opt[i+1] == TCPOLEN_MSS) {
 			u_int16_t oldmss;
 
 			oldmss = (opt[i+2] << 8) | opt[i+3];
 
-			if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
-			    oldmss <= newmss)
+			/* Never increase MSS, even when setting it, as
+			 * doing so results in problems for hosts that rely
+			 * on MSS being set correctly.
+			 */
+			if (oldmss <= newmss)
 				return 0;
 
 			opt[i+2] = (newmss & 0xff00) >> 8;
 			opt[i+3] = newmss & 0x00ff;
 
-			nf_proto_csum_replace2(&tcph->check, *pskb,
-					       htons(oldmss), htons(newmss), 0);
+			inet_proto_csum_replace2(&tcph->check, skb,
+						 htons(oldmss), htons(newmss),
+						 0);
 			return 0;
 		}
 	}
 
+	/* There is data after the header so the option can't be added
+	 * without moving it, and doing so may make the SYN packet
+	 * itself too large. Accept the packet unmodified instead.
+	 */
+	if (len > tcp_hdrlen)
+		return 0;
+
 	/*
 	 * MSS Option not found ?! add it..
 	 */
-	if (skb_tailroom((*pskb)) < TCPOLEN_MSS) {
-		struct sk_buff *newskb;
-
-		newskb = skb_copy_expand(*pskb, skb_headroom(*pskb),
-					 TCPOLEN_MSS, GFP_ATOMIC);
-		if (!newskb)
+	if (skb_tailroom(skb) < TCPOLEN_MSS) {
+		if (pskb_expand_head(skb, 0,
+				     TCPOLEN_MSS - skb_tailroom(skb),
+				     GFP_ATOMIC))
 			return -1;
-		kfree_skb(*pskb);
-		*pskb = newskb;
-		tcph = (struct tcphdr *)(skb_network_header(*pskb) + tcphoff);
+		tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
 	}
 
-	skb_put((*pskb), TCPOLEN_MSS);
+	skb_put(skb, TCPOLEN_MSS);
+
+	/*
+	 * IPv4: RFC 1122 states "If an MSS option is not received at
+	 * connection setup, TCP MUST assume a default send MSS of 536".
+	 * IPv6: RFC 2460 states IPv6 has a minimum MTU of 1280 and a minimum
+	 * length IPv6 header of 60, ergo the default MSS value is 1220
+	 * Since no MSS was provided, we must use the default values
+	 */
+	if (par->family == NFPROTO_IPV4)
+		newmss = min(newmss, (u16)536);
+	else
+		newmss = min(newmss, (u16)1220);
 
 	opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
-	memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
+	memmove(opt + TCPOLEN_MSS, opt, len - sizeof(struct tcphdr));
 
-	nf_proto_csum_replace2(&tcph->check, *pskb,
-			       htons(tcplen), htons(tcplen + TCPOLEN_MSS), 1);
+	inet_proto_csum_replace2(&tcph->check, skb,
+				 htons(len), htons(len + TCPOLEN_MSS), 1);
 	opt[0] = TCPOPT_MSS;
 	opt[1] = TCPOLEN_MSS;
 	opt[2] = (newmss & 0xff00) >> 8;
 	opt[3] = newmss & 0x00ff;
 
-	nf_proto_csum_replace4(&tcph->check, *pskb, 0, *((__be32 *)opt), 0);
+	inet_proto_csum_replace4(&tcph->check, skb, 0, *((__be32 *)opt), 0);
 
 	oldval = ((__be16 *)tcph)[6];
 	tcph->doff += TCPOLEN_MSS/4;
-	nf_proto_csum_replace2(&tcph->check, *pskb,
-				oldval, ((__be16 *)tcph)[6], 0);
+	inet_proto_csum_replace2(&tcph->check, skb,
+				 oldval, ((__be16 *)tcph)[6], 0);
 	return TCPOLEN_MSS;
 }
 
 static unsigned int
-xt_tcpmss_target4(struct sk_buff **pskb,
-		  const struct net_device *in,
-		  const struct net_device *out,
-		  unsigned int hooknum,
-		  const struct xt_target *target,
-		  const void *targinfo)
+tcpmss_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	struct iphdr *iph = ip_hdr(*pskb);
+	struct iphdr *iph = ip_hdr(skb);
 	__be16 newlen;
 	int ret;
 
-	ret = tcpmss_mangle_packet(pskb, targinfo, iph->ihl * 4,
+	ret = tcpmss_mangle_packet(skb, par,
+				   PF_INET,
+				   iph->ihl * 4,
 				   sizeof(*iph) + sizeof(struct tcphdr));
 	if (ret < 0)
 		return NF_DROP;
 	if (ret > 0) {
-		iph = ip_hdr(*pskb);
+		iph = ip_hdr(skb);
 		newlen = htons(ntohs(iph->tot_len) + ret);
-		nf_csum_replace2(&iph->check, iph->tot_len, newlen);
+		csum_replace2(&iph->check, iph->tot_len, newlen);
 		iph->tot_len = newlen;
 	}
 	return XT_CONTINUE;
 }
 
-#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
 static unsigned int
-xt_tcpmss_target6(struct sk_buff **pskb,
-		  const struct net_device *in,
-		  const struct net_device *out,
-		  unsigned int hooknum,
-		  const struct xt_target *target,
-		  const void *targinfo)
+tcpmss_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	struct ipv6hdr *ipv6h = ipv6_hdr(*pskb);
+	struct ipv6hdr *ipv6h = ipv6_hdr(skb);
 	u8 nexthdr;
+	__be16 frag_off;
 	int tcphoff;
 	int ret;
 
 	nexthdr = ipv6h->nexthdr;
-	tcphoff = ipv6_skip_exthdr(*pskb, sizeof(*ipv6h), &nexthdr);
-	if (tcphoff < 0) {
-		WARN_ON(1);
+	tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr, &frag_off);
+	if (tcphoff < 0)
 		return NF_DROP;
-	}
-	ret = tcpmss_mangle_packet(pskb, targinfo, tcphoff,
+	ret = tcpmss_mangle_packet(skb, par,
+				   PF_INET6,
+				   tcphoff,
 				   sizeof(*ipv6h) + sizeof(struct tcphdr));
 	if (ret < 0)
 		return NF_DROP;
 	if (ret > 0) {
-		ipv6h = ipv6_hdr(*pskb);
+		ipv6h = ipv6_hdr(skb);
 		ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
 	}
 	return XT_CONTINUE;
 }
 #endif
 
-#define TH_SYN 0x02
-
 /* Must specify -p tcp --syn */
 static inline bool find_syn_match(const struct xt_entry_match *m)
 {
 	const struct xt_tcp *tcpinfo = (const struct xt_tcp *)m->data;
 
 	if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
-	    tcpinfo->flg_cmp & TH_SYN &&
+	    tcpinfo->flg_cmp & TCPHDR_SYN &&
 	    !(tcpinfo->invflags & XT_TCP_INV_FLAGS))
 		return true;
 
 	return false;
 }
 
-static bool
-xt_tcpmss_checkentry4(const char *tablename,
-		      const void *entry,
-		      const struct xt_target *target,
-		      void *targinfo,
-		      unsigned int hook_mask)
+static int tcpmss_tg4_check(const struct xt_tgchk_param *par)
 {
-	const struct xt_tcpmss_info *info = targinfo;
-	const struct ipt_entry *e = entry;
+	const struct xt_tcpmss_info *info = par->targinfo;
+	const struct ipt_entry *e = par->entryinfo;
+	const struct xt_entry_match *ematch;
 
 	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
-	    (hook_mask & ~((1 << NF_IP_FORWARD) |
-			   (1 << NF_IP_LOCAL_OUT) |
-			   (1 << NF_IP_POST_ROUTING))) != 0) {
-		printk("xt_TCPMSS: path-MTU clamping only supported in "
-		       "FORWARD, OUTPUT and POSTROUTING hooks\n");
-		return false;
+	    (par->hook_mask & ~((1 << NF_INET_FORWARD) |
+			   (1 << NF_INET_LOCAL_OUT) |
+			   (1 << NF_INET_POST_ROUTING))) != 0) {
+		pr_info("path-MTU clamping only supported in "
+			"FORWARD, OUTPUT and POSTROUTING hooks\n");
+		return -EINVAL;
 	}
-	if (IPT_MATCH_ITERATE(e, find_syn_match))
-		return true;
-	printk("xt_TCPMSS: Only works on TCP SYN packets\n");
-	return false;
+	xt_ematch_foreach(ematch, e)
+		if (find_syn_match(ematch))
+			return 0;
+	pr_info("Only works on TCP SYN packets\n");
+	return -EINVAL;
 }
 
-#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
-static bool
-xt_tcpmss_checkentry6(const char *tablename,
-		      const void *entry,
-		      const struct xt_target *target,
-		      void *targinfo,
-		      unsigned int hook_mask)
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+static int tcpmss_tg6_check(const struct xt_tgchk_param *par)
 {
-	const struct xt_tcpmss_info *info = targinfo;
-	const struct ip6t_entry *e = entry;
+	const struct xt_tcpmss_info *info = par->targinfo;
+	const struct ip6t_entry *e = par->entryinfo;
+	const struct xt_entry_match *ematch;
 
 	if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
-	    (hook_mask & ~((1 << NF_IP6_FORWARD) |
-			   (1 << NF_IP6_LOCAL_OUT) |
-			   (1 << NF_IP6_POST_ROUTING))) != 0) {
-		printk("xt_TCPMSS: path-MTU clamping only supported in "
-		       "FORWARD, OUTPUT and POSTROUTING hooks\n");
-		return false;
+	    (par->hook_mask & ~((1 << NF_INET_FORWARD) |
+			   (1 << NF_INET_LOCAL_OUT) |
+			   (1 << NF_INET_POST_ROUTING))) != 0) {
+		pr_info("path-MTU clamping only supported in "
+			"FORWARD, OUTPUT and POSTROUTING hooks\n");
+		return -EINVAL;
 	}
-	if (IP6T_MATCH_ITERATE(e, find_syn_match))
-		return true;
-	printk("xt_TCPMSS: Only works on TCP SYN packets\n");
-	return false;
+	xt_ematch_foreach(ematch, e)
+		if (find_syn_match(ematch))
+			return 0;
+	pr_info("Only works on TCP SYN packets\n");
+	return -EINVAL;
 }
 #endif
 
-static struct xt_target xt_tcpmss_reg[] __read_mostly = {
+static struct xt_target tcpmss_tg_reg[] __read_mostly = {
 	{
-		.family		= AF_INET,
+		.family		= NFPROTO_IPV4,
 		.name		= "TCPMSS",
-		.checkentry	= xt_tcpmss_checkentry4,
-		.target		= xt_tcpmss_target4,
+		.checkentry	= tcpmss_tg4_check,
+		.target		= tcpmss_tg4,
 		.targetsize	= sizeof(struct xt_tcpmss_info),
 		.proto		= IPPROTO_TCP,
 		.me		= THIS_MODULE,
 	},
-#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
 	{
-		.family		= AF_INET6,
+		.family		= NFPROTO_IPV6,
 		.name		= "TCPMSS",
-		.checkentry	= xt_tcpmss_checkentry6,
-		.target		= xt_tcpmss_target6,
+		.checkentry	= tcpmss_tg6_check,
+		.target		= tcpmss_tg6,
 		.targetsize	= sizeof(struct xt_tcpmss_info),
 		.proto		= IPPROTO_TCP,
 		.me		= THIS_MODULE,
@@ -282,15 +330,15 @@ static struct xt_target xt_tcpmss_reg[] __read_mostly = {
 #endif
 };
 
-static int __init xt_tcpmss_init(void)
+static int __init tcpmss_tg_init(void)
 {
-	return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
+	return xt_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
 }
 
-static void __exit xt_tcpmss_fini(void)
+static void __exit tcpmss_tg_exit(void)
 {
-	xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
+	xt_unregister_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
 }
 
-module_init(xt_tcpmss_init);
-module_exit(xt_tcpmss_fini);
+module_init(tcpmss_tg_init);
+module_exit(tcpmss_tg_exit);