diff options
| -rw-r--r-- | include/linux/netfilter/xt_TCPOPTSTRIP.h | 13 | ||||
| -rw-r--r-- | net/netfilter/Kconfig | 8 | ||||
| -rw-r--r-- | net/netfilter/Makefile | 1 | ||||
| -rw-r--r-- | net/netfilter/xt_TCPOPTSTRIP.c | 147 |
4 files changed, 169 insertions, 0 deletions
diff --git a/include/linux/netfilter/xt_TCPOPTSTRIP.h b/include/linux/netfilter/xt_TCPOPTSTRIP.h new file mode 100644 index 0000000..2db5432 --- /dev/null +++ b/include/linux/netfilter/xt_TCPOPTSTRIP.h @@ -0,0 +1,13 @@ +#ifndef _XT_TCPOPTSTRIP_H +#define _XT_TCPOPTSTRIP_H + +#define tcpoptstrip_set_bit(bmap, idx) \ + (bmap[(idx) >> 5] |= 1U << (idx & 31)) +#define tcpoptstrip_test_bit(bmap, idx) \ + (((1U << (idx & 31)) & bmap[(idx) >> 5]) != 0) + +struct xt_tcpoptstrip_target_info { + u_int32_t strip_bmap[8]; +}; + +#endif /* _XT_TCPOPTSTRIP_H */ diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig index 21a9fcc..693f861 100644 --- a/net/netfilter/Kconfig +++ b/net/netfilter/Kconfig @@ -411,6 +411,14 @@ config NETFILTER_XT_TARGET_TCPMSS To compile it as a module, choose M here. If unsure, say N. +config NETFILTER_XT_TARGET_TCPOPTSTRIP + tristate '"TCPOPTSTRIP" target support (EXPERIMENTAL)' + depends on EXPERIMENTAL && NETFILTER_XTABLES + depends on IP_NF_MANGLE || IP6_NF_MANGLE + help + This option adds a "TCPOPTSTRIP" target, which allows you to strip + TCP options from TCP packets. + config NETFILTER_XT_MATCH_COMMENT tristate '"comment" match support' depends on NETFILTER_XTABLES diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile index ad0e36e..7763dea 100644 --- a/net/netfilter/Makefile +++ b/net/netfilter/Makefile @@ -48,6 +48,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o +obj-$(CONFIG_NETFILTER_XT_TARGET_TCPOPTSTRIP) += xt_TCPOPTSTRIP.o obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o # matches diff --git a/net/netfilter/xt_TCPOPTSTRIP.c b/net/netfilter/xt_TCPOPTSTRIP.c new file mode 100644 index 0000000..43d6ac2 --- /dev/null +++ b/net/netfilter/xt_TCPOPTSTRIP.c @@ -0,0 +1,147 @@ +/* + * 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 net_device *in, + const struct net_device *out, unsigned int hooknum, + const struct xt_target *target, const void *targinfo) +{ + return tcpoptstrip_mangle_packet(skb, 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 net_device *in, + const struct net_device *out, unsigned int hooknum, + const struct xt_target *target, const void *targinfo) +{ + struct ipv6hdr *ipv6h = ipv6_hdr(skb); + unsigned 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, targinfo, tcphoff, + sizeof(*ipv6h) + sizeof(struct tcphdr)); +} +#endif + +static struct xt_target tcpoptstrip_tg_reg[] __read_mostly = { + { + .name = "TCPOPTSTRIP", + .family = AF_INET, + .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 = AF_INET6, + .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("netfilter \"TCPOPTSTRIP\" target module"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("ipt_TCPOPTSTRIP"); +MODULE_ALIAS("ip6t_TCPOPTSTRIP"); |