diff options
Diffstat (limited to 'net/netfilter/xt_TCPOPTSTRIP.c')
| -rw-r--r-- | net/netfilter/xt_TCPOPTSTRIP.c | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/net/netfilter/xt_TCPOPTSTRIP.c b/net/netfilter/xt_TCPOPTSTRIP.c new file mode 100644 index 0000000..9dd8c8e --- /dev/null +++ b/net/netfilter/xt_TCPOPTSTRIP.c @@ -0,0 +1,143 @@ +/* + * A module for stripping a specific TCP option from TCP packets. + * + * Copyright (C) 2007 Sven Schnelle <svens@bitebene.org> + * Copyright © CC Computer Consultants GmbH, 2007 + * Contact: Jan Engelhardt <jengelh@computergmbh.de> + * + * 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/x_tables.h> +#include <linux/netfilter/xt_TCPOPTSTRIP.h> + +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 +tcpoptstrip_mangle_packet(struct sk_buff *skb, + const struct xt_tcpoptstrip_target_info *info, + unsigned int tcphoff, unsigned int minlen) +{ + unsigned int optl, i, j; + struct tcphdr *tcph; + u_int16_t n, o; + u_int8_t *opt; + + if (!skb_make_writable(skb, skb->len)) + return NF_DROP; + + tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff); + opt = (u_int8_t *)tcph; + + /* + * Walk through all TCP options - if we find some option to remove, + * set all octets to %TCPOPT_NOP and adjust checksum. + */ + for (i = sizeof(struct tcphdr); i < tcp_hdrlen(skb); i += optl) { + optl = optlen(opt, i); + + if (i + optl > tcp_hdrlen(skb)) + break; + + if (!tcpoptstrip_test_bit(info->strip_bmap, opt[i])) + continue; + + for (j = 0; j < optl; ++j) { + o = opt[i+j]; + n = TCPOPT_NOP; + if ((i + j) % 2 == 0) { + o <<= 8; + n <<= 8; + } + inet_proto_csum_replace2(&tcph->check, skb, htons(o), + htons(n), 0); + } + memset(opt + i, TCPOPT_NOP, optl); + } + + return XT_CONTINUE; +} + +static unsigned int +tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_target_param *par) +{ + return tcpoptstrip_mangle_packet(skb, par->targinfo, ip_hdrlen(skb), + sizeof(struct iphdr) + sizeof(struct tcphdr)); +} + +#if defined(CONFIG_IP6_NF_MANGLE) || defined(CONFIG_IP6_NF_MANGLE_MODULE) +static unsigned int +tcpoptstrip_tg6(struct sk_buff *skb, const struct xt_target_param *par) +{ + struct ipv6hdr *ipv6h = ipv6_hdr(skb); + int tcphoff; + u_int8_t nexthdr; + + nexthdr = ipv6h->nexthdr; + tcphoff = ipv6_skip_exthdr(skb, sizeof(*ipv6h), &nexthdr); + if (tcphoff < 0) + return NF_DROP; + + return tcpoptstrip_mangle_packet(skb, par->targinfo, tcphoff, + sizeof(*ipv6h) + sizeof(struct tcphdr)); +} +#endif + +static struct xt_target tcpoptstrip_tg_reg[] __read_mostly = { + { + .name = "TCPOPTSTRIP", + .family = NFPROTO_IPV4, + .table = "mangle", + .proto = IPPROTO_TCP, + .target = tcpoptstrip_tg4, + .targetsize = sizeof(struct xt_tcpoptstrip_target_info), + .me = THIS_MODULE, + }, +#if defined(CONFIG_IP6_NF_MANGLE) || defined(CONFIG_IP6_NF_MANGLE_MODULE) + { + .name = "TCPOPTSTRIP", + .family = NFPROTO_IPV6, + .table = "mangle", + .proto = IPPROTO_TCP, + .target = tcpoptstrip_tg6, + .targetsize = sizeof(struct xt_tcpoptstrip_target_info), + .me = THIS_MODULE, + }, +#endif +}; + +static int __init tcpoptstrip_tg_init(void) +{ + return xt_register_targets(tcpoptstrip_tg_reg, + ARRAY_SIZE(tcpoptstrip_tg_reg)); +} + +static void __exit tcpoptstrip_tg_exit(void) +{ + xt_unregister_targets(tcpoptstrip_tg_reg, + ARRAY_SIZE(tcpoptstrip_tg_reg)); +} + +module_init(tcpoptstrip_tg_init); +module_exit(tcpoptstrip_tg_exit); +MODULE_AUTHOR("Sven Schnelle <svens@bitebene.org>, Jan Engelhardt <jengelh@computergmbh.de>"); +MODULE_DESCRIPTION("Xtables: TCP option stripping"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("ipt_TCPOPTSTRIP"); +MODULE_ALIAS("ip6t_TCPOPTSTRIP"); |
