From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Apr 2005 15:20:36 -0700 Subject: Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip! --- net/ipv4/netfilter/ipt_TCPMSS.c | 262 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 262 insertions(+) create mode 100644 net/ipv4/netfilter/ipt_TCPMSS.c (limited to 'net/ipv4/netfilter/ipt_TCPMSS.c') diff --git a/net/ipv4/netfilter/ipt_TCPMSS.c b/net/ipv4/netfilter/ipt_TCPMSS.c new file mode 100644 index 00000000000..1049050b2bf --- /dev/null +++ b/net/ipv4/netfilter/ipt_TCPMSS.c @@ -0,0 +1,262 @@ +/* + * This is a module which is used for setting the MSS option in TCP packets. + * + * Copyright (C) 2000 Marc Boucher + * + * 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 +#include + +#include +#include + +#include +#include + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Marc Boucher "); +MODULE_DESCRIPTION("iptables TCP MSS modification module"); + +#if 0 +#define DEBUGP printk +#else +#define DEBUGP(format, args...) +#endif + +static u_int16_t +cheat_check(u_int32_t oldvalinv, u_int32_t newval, u_int16_t oldcheck) +{ + u_int32_t diffs[] = { oldvalinv, newval }; + return csum_fold(csum_partial((char *)diffs, sizeof(diffs), + oldcheck^0xFFFF)); +} + +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 void *targinfo, + void *userinfo) +{ + const struct ipt_tcpmss_info *tcpmssinfo = targinfo; + struct tcphdr *tcph; + struct iphdr *iph; + u_int16_t tcplen, newtotlen, oldval, newmss; + unsigned int i; + u_int8_t *opt; + + if (!skb_ip_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(!(*pskb)->dst) { + if (net_ratelimit()) + printk(KERN_ERR + "ipt_tcpmss_target: no dst?! can't determine path-MTU\n"); + return NF_DROP; /* or IPT_CONTINUE ?? */ + } + + 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); + + tcph->check = cheat_check(htons(oldmss)^0xFFFF, + htons(newmss), + tcph->check); + + DEBUGP(KERN_INFO "ipt_tcpmss_target: %u.%u.%u.%u:%hu" + "->%u.%u.%u.%u:%hu changed TCP MSS option" + " (from %u to %u)\n", + NIPQUAD((*pskb)->nh.iph->saddr), + ntohs(tcph->source), + NIPQUAD((*pskb)->nh.iph->daddr), + ntohs(tcph->dest), + oldmss, newmss); + goto retmodified; + } + } + + /* + * 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 (net_ratelimit()) + printk(KERN_ERR "ipt_tcpmss_target:" + " unable to allocate larger skb\n"); + 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)); + + tcph->check = cheat_check(htons(tcplen) ^ 0xFFFF, + htons(tcplen + TCPOLEN_MSS), tcph->check); + tcplen += TCPOLEN_MSS; + + opt[0] = TCPOPT_MSS; + opt[1] = TCPOLEN_MSS; + opt[2] = (newmss & 0xff00) >> 8; + opt[3] = (newmss & 0x00ff); + + tcph->check = cheat_check(~0, *((u_int32_t *)opt), tcph->check); + + oldval = ((u_int16_t *)tcph)[6]; + tcph->doff += TCPOLEN_MSS/4; + tcph->check = cheat_check(oldval ^ 0xFFFF, + ((u_int16_t *)tcph)[6], tcph->check); + + newtotlen = htons(ntohs(iph->tot_len) + TCPOLEN_MSS); + iph->check = cheat_check(iph->tot_len ^ 0xFFFF, + newtotlen, iph->check); + iph->tot_len = newtotlen; + + DEBUGP(KERN_INFO "ipt_tcpmss_target: %u.%u.%u.%u:%hu" + "->%u.%u.%u.%u:%hu added TCP MSS option (%u)\n", + NIPQUAD((*pskb)->nh.iph->saddr), + ntohs(tcph->source), + NIPQUAD((*pskb)->nh.iph->daddr), + ntohs(tcph->dest), + newmss); + + retmodified: + /* We never hw checksum SYN packets. */ + BUG_ON((*pskb)->ip_summed == CHECKSUM_HW); + + (*pskb)->nfcache |= NFC_UNKNOWN | NFC_ALTERED; + 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 struct ipt_entry *e, + void *targinfo, + unsigned int targinfosize, + unsigned int hook_mask) +{ + const struct ipt_tcpmss_info *tcpmssinfo = targinfo; + + if (targinfosize != IPT_ALIGN(sizeof(struct ipt_tcpmss_info))) { + DEBUGP("ipt_tcpmss_checkentry: targinfosize %u != %u\n", + targinfosize, IPT_ALIGN(sizeof(struct ipt_tcpmss_info))); + return 0; + } + + + 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 (e->ip.proto == IPPROTO_TCP + && !(e->ip.invflags & IPT_INV_PROTO) + && 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, + .checkentry = ipt_tcpmss_checkentry, + .me = THIS_MODULE, +}; + +static int __init init(void) +{ + return ipt_register_target(&ipt_tcpmss_reg); +} + +static void __exit fini(void) +{ + ipt_unregister_target(&ipt_tcpmss_reg); +} + +module_init(init); +module_exit(fini); -- cgit v1.2.3