Netfilter: Import xt_TCPOPTSTRIP
Originally from Sven Schnelle.
xt_TCPOPTSTRIP can strip TCP options from TCP packets, for example,
to disable Selective ACK or Window scaling.
Signed-off-by: Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxx>
---
include/linux/netfilter/xt_TCPOPTSTRIP.h | 13 ++
net/netfilter/Kconfig | 8 +
net/netfilter/Makefile | 1
net/netfilter/xt_TCPOPTSTRIP.c | 143 +++++++++++++++++++++++++++++++
4 files changed, 165 insertions(+)
Index: linux-2.6/include/linux/netfilter/xt_TCPOPTSTRIP.h
===================================================================
--- /dev/null
+++ linux-2.6/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] |= 1UL << (idx & 31))
+#define tcpoptstrip_test_bit(bmap, idx) \
+ (((1UL << (idx & 31)) & bmap[(idx) >> 5]) != 0)
+
+struct xt_tcpoptstrip_target_info {
+ u_int32_t strip_bmap[8];
+};
+
+#endif /* _XT_TCPOPTSTRIP_H */
Index: linux-2.6/net/netfilter/Kconfig
===================================================================
--- linux-2.6.orig/net/netfilter/Kconfig
+++ linux-2.6/net/netfilter/Kconfig
@@ -424,6 +424,14 @@ config NETFILTER_XT_TARGET_TEE
Documentation/modules.txt. The module will be called xt_TEE.ko.
If unsure, say N.
+config NETFILTER_XT_TARGET_TCPOPTSTRIP
+ tristate '"TCPOPTSTRIP" target support'
+ depends on 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
Index: linux-2.6/net/netfilter/Makefile
===================================================================
--- linux-2.6.orig/net/netfilter/Makefile
+++ linux-2.6/net/netfilter/Makefile
@@ -48,6 +48,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE
obj-$(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_TEE) += xt_TEE.o
obj-$(CONFIG_NETFILTER_XT_TARGET_TRACE) += xt_TRACE.o
Index: linux-2.6/net/netfilter/xt_TCPOPTSTRIP.c
===================================================================
--- /dev/null
+++ linux-2.6/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@xxxxxxxxxxxx>
+ * Copyright © CC Computer Consultants GmbH, 2007
+ * Contact: Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx>
+ *
+ * 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;
+ }
+ nf_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));
+}
+
+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));
+}
+
+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,
+ },
+ {
+ .name = "TCPOPTSTRIP",
+ .family = AF_INET6,
+ .table = "mangle",
+ .proto = IPPROTO_TCP,
+ .target = tcpoptstrip_tg6,
+ .targetsize = sizeof(struct xt_tcpoptstrip_target_info),
+ .me = THIS_MODULE,
+ },
+};
+
+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@xxxxxxxxxxxx>, Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("netfilter \"TCPOPTSTRIP\" target module");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_TCPOPTSTRIP");
+MODULE_ALIAS("ip6t_TCPOPTSTRIP");
-
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
