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Diffstat (limited to 'net/netfilter/xt_TCPMSS.c')
-rw-r--r--net/netfilter/xt_TCPMSS.c296
1 files changed, 296 insertions, 0 deletions
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
new file mode 100644
index 000000000000..db7e38c08de2
--- /dev/null
+++ b/net/netfilter/xt_TCPMSS.c
@@ -0,0 +1,296 @@
+/*
+ * 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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