diff options
Diffstat (limited to 'net/netfilter/xt_TCPMSS.c')
| -rw-r--r-- | net/netfilter/xt_TCPMSS.c | 296 |
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); |