| // SPDX-License-Identifier: GPL-2.0-only |
| /* Kernel module to match TCP MSS values. */ |
| |
| /* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca> |
| * Portions (C) 2005 by Harald Welte <laforge@netfilter.org> |
| */ |
| |
| #include <linux/module.h> |
| #include <linux/skbuff.h> |
| #include <net/tcp.h> |
| |
| #include <linux/netfilter/xt_tcpmss.h> |
| #include <linux/netfilter/x_tables.h> |
| |
| #include <linux/netfilter_ipv4/ip_tables.h> |
| #include <linux/netfilter_ipv6/ip6_tables.h> |
| |
| MODULE_LICENSE("GPL"); |
| MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>"); |
| MODULE_DESCRIPTION("Xtables: TCP MSS match"); |
| MODULE_ALIAS("ipt_tcpmss"); |
| MODULE_ALIAS("ip6t_tcpmss"); |
| |
| static bool |
| tcpmss_mt(const struct sk_buff *skb, struct xt_action_param *par) |
| { |
| const struct xt_tcpmss_match_info *info = par->matchinfo; |
| const struct tcphdr *th; |
| struct tcphdr _tcph; |
| /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */ |
| const u_int8_t *op; |
| u8 _opt[15 * 4 - sizeof(_tcph)]; |
| unsigned int i, optlen; |
| |
| /* If we don't have the whole header, drop packet. */ |
| th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph); |
| if (th == NULL) |
| goto dropit; |
| |
| /* Malformed. */ |
| if (th->doff*4 < sizeof(*th)) |
| goto dropit; |
| |
| optlen = th->doff*4 - sizeof(*th); |
| if (!optlen) |
| goto out; |
| |
| /* Truncated options. */ |
| op = skb_header_pointer(skb, par->thoff + sizeof(*th), optlen, _opt); |
| if (op == NULL) |
| goto dropit; |
| |
| for (i = 0; i < optlen; ) { |
| if (op[i] == TCPOPT_MSS |
| && (optlen - i) >= TCPOLEN_MSS |
| && op[i+1] == TCPOLEN_MSS) { |
| u_int16_t mssval; |
| |
| mssval = (op[i+2] << 8) | op[i+3]; |
| |
| return (mssval >= info->mss_min && |
| mssval <= info->mss_max) ^ info->invert; |
| } |
| if (op[i] < 2) |
| i++; |
| else |
| i += op[i+1] ? : 1; |
| } |
| out: |
| return info->invert; |
| |
| dropit: |
| par->hotdrop = true; |
| return false; |
| } |
| |
| static struct xt_match tcpmss_mt_reg[] __read_mostly = { |
| { |
| .name = "tcpmss", |
| .family = NFPROTO_IPV4, |
| .match = tcpmss_mt, |
| .matchsize = sizeof(struct xt_tcpmss_match_info), |
| .proto = IPPROTO_TCP, |
| .me = THIS_MODULE, |
| }, |
| { |
| .name = "tcpmss", |
| .family = NFPROTO_IPV6, |
| .match = tcpmss_mt, |
| .matchsize = sizeof(struct xt_tcpmss_match_info), |
| .proto = IPPROTO_TCP, |
| .me = THIS_MODULE, |
| }, |
| }; |
| |
| static int __init tcpmss_mt_init(void) |
| { |
| return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg)); |
| } |
| |
| static void __exit tcpmss_mt_exit(void) |
| { |
| xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg)); |
| } |
| |
| module_init(tcpmss_mt_init); |
| module_exit(tcpmss_mt_exit); |