header-y += xt_tcpudp.h
header-y += xt_SECMARK.h
header-y += xt_CONNSECMARK.h
+header-y += xt_TCPMSS.h
unifdef-y += nf_conntrack_common.h
unifdef-y += nf_conntrack_ftp.h
--- /dev/null
+#ifndef _XT_TCPMSS_H
+#define _XT_TCPMSS_H
+
+struct xt_tcpmss_info {
+ u_int16_t mss;
+};
+
+#define XT_TCPMSS_CLAMP_PMTU 0xffff
+
+#endif /* _XT_TCPMSS_H */
#ifndef _IPT_TCPMSS_H
#define _IPT_TCPMSS_H
-struct ipt_tcpmss_info {
- u_int16_t mss;
-};
+#include <linux/netfilter/xt_TCPMSS.h>
-#define IPT_TCPMSS_CLAMP_PMTU 0xffff
+#define ipt_tcpmss_info xt_tcpmss_info
+#define IPT_TCPMSS_CLAMP_PMTU XT_TCPMSS_CLAMP_PMTU
#endif /*_IPT_TCPMSS_H*/
To compile it as a module, choose M here. If unsure, say N.
-config IP_NF_TARGET_TCPMSS
- tristate "TCPMSS target support"
- depends on IP_NF_IPTABLES
- ---help---
- This option adds a `TCPMSS' target, which allows you to alter the
- MSS value of TCP SYN packets, to control the maximum size for that
- connection (usually limiting it to your outgoing interface's MTU
- minus 40).
-
- This is used to overcome criminally braindead ISPs or servers which
- block ICMP Fragmentation Needed packets. The symptoms of this
- problem are that everything works fine from your Linux
- firewall/router, but machines behind it can never exchange large
- packets:
- 1) Web browsers connect, then hang with no data received.
- 2) Small mail works fine, but large emails hang.
- 3) ssh works fine, but scp hangs after initial handshaking.
-
- Workaround: activate this option and add a rule to your firewall
- configuration like:
-
- iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
- -j TCPMSS --clamp-mss-to-pmtu
-
- To compile it as a module, choose M here. If unsure, say N.
-
# NAT + specific targets: ip_conntrack
config IP_NF_NAT
tristate "Full NAT"
obj-$(CONFIG_IP_NF_NAT_SNMP_BASIC) += ip_nat_snmp_basic.o
obj-$(CONFIG_IP_NF_TARGET_LOG) += ipt_LOG.o
obj-$(CONFIG_IP_NF_TARGET_ULOG) += ipt_ULOG.o
-obj-$(CONFIG_IP_NF_TARGET_TCPMSS) += ipt_TCPMSS.o
obj-$(CONFIG_IP_NF_TARGET_CLUSTERIP) += ipt_CLUSTERIP.o
obj-$(CONFIG_IP_NF_TARGET_TTL) += ipt_TTL.o
+++ /dev/null
-/*
- * This is a module which is used for setting the MSS option in TCP packets.
- *
- * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
- *
- * 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.
- */
-
-#include <linux/module.h>
-#include <linux/skbuff.h>
-
-#include <linux/ip.h>
-#include <net/tcp.h>
-
-#include <linux/netfilter_ipv4/ip_tables.h>
-#include <linux/netfilter_ipv4/ipt_TCPMSS.h>
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
-MODULE_DESCRIPTION("iptables TCP MSS modification module");
-
-static inline unsigned int
-optlen(const u_int8_t *opt, unsigned int offset)
-{
- /* Beware zero-length options: make finite progress */
- if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0)
- return 1;
- else
- return opt[offset+1];
-}
-
-static unsigned int
-ipt_tcpmss_target(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)
-{
- const struct ipt_tcpmss_info *tcpmssinfo = targinfo;
- struct tcphdr *tcph;
- struct iphdr *iph;
- u_int16_t tcplen, newmss;
- __be16 newtotlen, oldval;
- unsigned int i;
- u_int8_t *opt;
-
- if (!skb_make_writable(pskb, (*pskb)->len))
- return NF_DROP;
-
- iph = (*pskb)->nh.iph;
- tcplen = (*pskb)->len - iph->ihl*4;
- tcph = (void *)iph + iph->ihl*4;
-
- /* 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
- "ipt_tcpmss_target: bad length (%d bytes)\n",
- (*pskb)->len);
- return NF_DROP;
- }
-
- if (tcpmssinfo->mss == IPT_TCPMSS_CLAMP_PMTU) {
- if (dst_mtu((*pskb)->dst) <= sizeof(struct iphdr) +
- sizeof(struct tcphdr)) {
- if (net_ratelimit())
- printk(KERN_ERR "ipt_tcpmss_target: "
- "unknown or invalid path-MTU (%d)\n",
- dst_mtu((*pskb)->dst));
- return NF_DROP; /* or IPT_CONTINUE ?? */
- }
-
- newmss = dst_mtu((*pskb)->dst) - sizeof(struct iphdr) -
- sizeof(struct tcphdr);
- } else
- newmss = tcpmssinfo->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) {
- u_int16_t oldmss;
-
- oldmss = (opt[i+2] << 8) | opt[i+3];
-
- if (tcpmssinfo->mss == IPT_TCPMSS_CLAMP_PMTU &&
- oldmss <= newmss)
- return IPT_CONTINUE;
-
- opt[i+2] = (newmss & 0xff00) >> 8;
- opt[i+3] = (newmss & 0x00ff);
-
- nf_proto_csum_replace2(&tcph->check, *pskb,
- htons(oldmss), htons(newmss), 0);
- return IPT_CONTINUE;
- }
- }
-
- /*
- * 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)
- return NF_DROP;
- kfree_skb(*pskb);
- *pskb = newskb;
- iph = (*pskb)->nh.iph;
- tcph = (void *)iph + iph->ihl*4;
- }
-
- skb_put((*pskb), TCPOLEN_MSS);
-
- opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
- memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
-
- nf_proto_csum_replace2(&tcph->check, *pskb,
- htons(tcplen), htons(tcplen + 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);
-
- oldval = ((__be16 *)tcph)[6];
- tcph->doff += TCPOLEN_MSS/4;
- nf_proto_csum_replace2(&tcph->check, *pskb,
- oldval, ((__be16 *)tcph)[6], 0);
-
- newtotlen = htons(ntohs(iph->tot_len) + TCPOLEN_MSS);
- nf_csum_replace2(&iph->check, iph->tot_len, newtotlen);
- iph->tot_len = newtotlen;
- return IPT_CONTINUE;
-}
-
-#define TH_SYN 0x02
-
-static inline int find_syn_match(const struct ipt_entry_match *m)
-{
- const struct ipt_tcp *tcpinfo = (const struct ipt_tcp *)m->data;
-
- if (strcmp(m->u.kernel.match->name, "tcp") == 0 &&
- tcpinfo->flg_cmp & TH_SYN &&
- !(tcpinfo->invflags & IPT_TCP_INV_FLAGS))
- return 1;
-
- return 0;
-}
-
-/* Must specify -p tcp --syn/--tcp-flags SYN */
-static int
-ipt_tcpmss_checkentry(const char *tablename,
- const void *e_void,
- const struct xt_target *target,
- void *targinfo,
- unsigned int hook_mask)
-{
- const struct ipt_tcpmss_info *tcpmssinfo = targinfo;
- const struct ipt_entry *e = e_void;
-
- if (tcpmssinfo->mss == IPT_TCPMSS_CLAMP_PMTU &&
- (hook_mask & ~((1 << NF_IP_FORWARD) |
- (1 << NF_IP_LOCAL_OUT) |
- (1 << NF_IP_POST_ROUTING))) != 0) {
- printk("TCPMSS: path-MTU clamping only supported in "
- "FORWARD, OUTPUT and POSTROUTING hooks\n");
- return 0;
- }
-
- if (IPT_MATCH_ITERATE(e, find_syn_match))
- return 1;
- printk("TCPMSS: Only works on TCP SYN packets\n");
- return 0;
-}
-
-static struct ipt_target ipt_tcpmss_reg = {
- .name = "TCPMSS",
- .target = ipt_tcpmss_target,
- .targetsize = sizeof(struct ipt_tcpmss_info),
- .proto = IPPROTO_TCP,
- .checkentry = ipt_tcpmss_checkentry,
- .me = THIS_MODULE,
-};
-
-static int __init ipt_tcpmss_init(void)
-{
- return ipt_register_target(&ipt_tcpmss_reg);
-}
-
-static void __exit ipt_tcpmss_fini(void)
-{
- ipt_unregister_target(&ipt_tcpmss_reg);
-}
-
-module_init(ipt_tcpmss_init);
-module_exit(ipt_tcpmss_fini);
To compile it as a module, choose M here. If unsure, say N.
+config NETFILTER_XT_TARGET_TCPMSS
+ tristate '"TCPMSS" target support'
+ depends on NETFILTER_XTABLES && (IPV6 || IPV6=n)
+ ---help---
+ This option adds a `TCPMSS' target, which allows you to alter the
+ MSS value of TCP SYN packets, to control the maximum size for that
+ connection (usually limiting it to your outgoing interface's MTU
+ minus 40).
+
+ This is used to overcome criminally braindead ISPs or servers which
+ block ICMP Fragmentation Needed packets. The symptoms of this
+ problem are that everything works fine from your Linux
+ firewall/router, but machines behind it can never exchange large
+ packets:
+ 1) Web browsers connect, then hang with no data received.
+ 2) Small mail works fine, but large emails hang.
+ 3) ssh works fine, but scp hangs after initial handshaking.
+
+ Workaround: activate this option and add a rule to your firewall
+ configuration like:
+
+ iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
+ -j TCPMSS --clamp-mss-to-pmtu
+
+ To compile it as a module, choose M here. If unsure, say N.
+
config NETFILTER_XT_MATCH_COMMENT
tristate '"comment" match support'
depends on NETFILTER_XTABLES
obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o
obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o
obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o
obj-$(CONFIG_NETFILTER_XT_TARGET_CONNSECMARK) += xt_CONNSECMARK.o
# matches
--- /dev/null
+/*
+ * This is a module which is used for setting the MSS option in TCP packets.
+ *
+ * Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
+ *
+ * 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.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
+#include <net/ipv6.h>
+#include <net/tcp.h>
+
+#include <linux/netfilter_ipv4/ip_tables.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_tcpudp.h>
+#include <linux/netfilter/xt_TCPMSS.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
+MODULE_DESCRIPTION("x_tables TCP MSS modification module");
+MODULE_ALIAS("ipt_TCPMSS");
+MODULE_ALIAS("ip6t_TCPMSS");
+
+static inline unsigned int
+optlen(const u_int8_t *opt, unsigned int offset)
+{
+ /* Beware zero-length options: make finite progress */
+ if (opt[offset] <= TCPOPT_NOP || opt[offset+1] == 0)
+ return 1;
+ else
+ return opt[offset+1];
+}
+
+static int
+tcpmss_mangle_packet(struct sk_buff **pskb,
+ const struct xt_tcpmss_info *info,
+ unsigned int tcphoff,
+ unsigned int minlen)
+{
+ struct tcphdr *tcph;
+ unsigned int tcplen, i;
+ __be16 oldval;
+ u16 newmss;
+ u8 *opt;
+
+ if (!skb_make_writable(pskb, (*pskb)->len))
+ return -1;
+
+ tcplen = (*pskb)->len - tcphoff;
+ tcph = (struct tcphdr *)((*pskb)->nh.raw + 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);
+ 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));
+ return -1;
+ }
+ newmss = dst_mtu((*pskb)->dst) - 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) {
+ u_int16_t oldmss;
+
+ oldmss = (opt[i+2] << 8) | opt[i+3];
+
+ if (info->mss == XT_TCPMSS_CLAMP_PMTU &&
+ 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);
+ 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)
+ return -1;
+ kfree_skb(*pskb);
+ *pskb = newskb;
+ tcph = (struct tcphdr *)((*pskb)->nh.raw + tcphoff);
+ }
+
+ skb_put((*pskb), TCPOLEN_MSS);
+
+ opt = (u_int8_t *)tcph + sizeof(struct tcphdr);
+ memmove(opt + TCPOLEN_MSS, opt, tcplen - sizeof(struct tcphdr));
+
+ nf_proto_csum_replace2(&tcph->check, *pskb,
+ htons(tcplen), htons(tcplen + 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);
+
+ oldval = ((__be16 *)tcph)[6];
+ tcph->doff += TCPOLEN_MSS/4;
+ nf_proto_csum_replace2(&tcph->check, *pskb,
+ 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)
+{
+ struct iphdr *iph = (*pskb)->nh.iph;
+ __be16 newlen;
+ int ret;
+
+ ret = tcpmss_mangle_packet(pskb, targinfo, iph->ihl * 4,
+ sizeof(*iph) + sizeof(struct tcphdr));
+ if (ret < 0)
+ return NF_DROP;
+ if (ret > 0) {
+ iph = (*pskb)->nh.iph;
+ newlen = htons(ntohs(iph->tot_len) + ret);
+ nf_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)
+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)
+{
+ struct ipv6hdr *ipv6h = (*pskb)->nh.ipv6h;
+ u8 nexthdr;
+ int tcphoff;
+ int ret;
+
+ nexthdr = ipv6h->nexthdr;
+ tcphoff = ipv6_skip_exthdr(*pskb, sizeof(*ipv6h), &nexthdr);
+ if (tcphoff < 0) {
+ WARN_ON(1);
+ return NF_DROP;
+ }
+ ret = tcpmss_mangle_packet(pskb, targinfo, tcphoff,
+ sizeof(*ipv6h) + sizeof(struct tcphdr));
+ if (ret < 0)
+ return NF_DROP;
+ if (ret > 0) {
+ ipv6h = (*pskb)->nh.ipv6h;
+ ipv6h->payload_len = htons(ntohs(ipv6h->payload_len) + ret);
+ }
+ return XT_CONTINUE;
+}
+#endif
+
+#define TH_SYN 0x02
+
+/* Must specify -p tcp --syn */
+static inline int 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->invflags & XT_TCP_INV_FLAGS))
+ return 1;
+
+ return 0;
+}
+
+static int
+xt_tcpmss_checkentry4(const char *tablename,
+ const void *entry,
+ const struct xt_target *target,
+ void *targinfo,
+ unsigned int hook_mask)
+{
+ const struct xt_tcpmss_info *info = targinfo;
+ const struct ipt_entry *e = entry;
+
+ 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 0;
+ }
+ if (IPT_MATCH_ITERATE(e, find_syn_match))
+ return 1;
+ printk("xt_TCPMSS: Only works on TCP SYN packets\n");
+ return 0;
+}
+
+#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
+static int
+xt_tcpmss_checkentry6(const char *tablename,
+ const void *entry,
+ const struct xt_target *target,
+ void *targinfo,
+ unsigned int hook_mask)
+{
+ const struct xt_tcpmss_info *info = targinfo;
+ const struct ip6t_entry *e = entry;
+
+ 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 0;
+ }
+ if (IP6T_MATCH_ITERATE(e, find_syn_match))
+ return 1;
+ printk("xt_TCPMSS: Only works on TCP SYN packets\n");
+ return 0;
+}
+#endif
+
+static struct xt_target xt_tcpmss_reg[] = {
+ {
+ .family = AF_INET,
+ .name = "TCPMSS",
+ .checkentry = xt_tcpmss_checkentry4,
+ .target = xt_tcpmss_target4,
+ .targetsize = sizeof(struct xt_tcpmss_info),
+ .proto = IPPROTO_TCP,
+ .me = THIS_MODULE,
+ },
+#if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
+ {
+ .family = AF_INET6,
+ .name = "TCPMSS",
+ .checkentry = xt_tcpmss_checkentry6,
+ .target = xt_tcpmss_target6,
+ .targetsize = sizeof(struct xt_tcpmss_info),
+ .proto = IPPROTO_TCP,
+ .me = THIS_MODULE,
+ },
+#endif
+};
+
+static int __init xt_tcpmss_init(void)
+{
+ return xt_register_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
+}
+
+static void __exit xt_tcpmss_fini(void)
+{
+ xt_unregister_targets(xt_tcpmss_reg, ARRAY_SIZE(xt_tcpmss_reg));
+}
+
+module_init(xt_tcpmss_init);
+module_exit(xt_tcpmss_fini);
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