// SPDX-License-Identifier: GPL-2.0-only /* * TTL modification target for IP tables * (C) 2000,2005 by Harald Welte <laforge@netfilter.org> * * Hop Limit modification target for ip6tables * Maciej Soltysiak <solt@dns.toxicfilms.tv> */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/module.h> #include <linux/skbuff.h> #include <linux/ip.h> #include <linux/ipv6.h> #include <net/checksum.h> #include <linux/netfilter/x_tables.h> #include <linux/netfilter_ipv4/ipt_TTL.h> #include <linux/netfilter_ipv6/ip6t_HL.h> MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>"); MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>"); MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target"); MODULE_LICENSE("GPL"); static unsigned int ttl_tg(struct sk_buff *skb, const struct xt_action_param *par) { struct iphdr *iph; const struct ipt_TTL_info *info = par->targinfo; int new_ttl; if (skb_ensure_writable(skb, sizeof(*iph))) return NF_DROP; iph = ip_hdr(skb); switch (info->mode) { case IPT_TTL_SET: new_ttl = info->ttl; break; case IPT_TTL_INC: new_ttl = iph->ttl + info->ttl; if (new_ttl > 255) new_ttl = 255; break; case IPT_TTL_DEC: new_ttl = iph->ttl - info->ttl; if (new_ttl < 0) new_ttl = 0; break; default: new_ttl = iph->ttl; break; } if (new_ttl != iph->ttl) { csum_replace2(&iph->check, htons(iph->ttl << 8), htons(new_ttl << 8)); iph->ttl = new_ttl; } return XT_CONTINUE; } static unsigned int hl_tg6(struct sk_buff *skb, const struct xt_action_param *par) { struct ipv6hdr *ip6h; const struct ip6t_HL_info *info = par->targinfo; int new_hl; if (skb_ensure_writable(skb, sizeof(*ip6h))) return NF_DROP; ip6h = ipv6_hdr(skb); switch (info->mode) { case IP6T_HL_SET: new_hl = info->hop_limit; break; case IP6T_HL_INC: new_hl = ip6h->hop_limit + info->hop_limit; if (new_hl > 255) new_hl = 255; break; case IP6T_HL_DEC: new_hl = ip6h->hop_limit - info->hop_limit; if (new_hl < 0) new_hl = 0; break; default: new_hl = ip6h->hop_limit; break; } ip6h->hop_limit = new_hl; return XT_CONTINUE; } static int ttl_tg_check(const struct xt_tgchk_param *par) { const struct ipt_TTL_info *info = par->targinfo; if (info->mode > IPT_TTL_MAXMODE) return -EINVAL; if (info->mode != IPT_TTL_SET && info->ttl == 0) return -EINVAL; return 0; } static int hl_tg6_check(const struct xt_tgchk_param *par) { const struct ip6t_HL_info *info = par->targinfo; if (info->mode > IP6T_HL_MAXMODE) return -EINVAL; if (info->mode != IP6T_HL_SET && info->hop_limit == 0) return -EINVAL; return 0; } static struct xt_target hl_tg_reg[] __read_mostly = { { .name = "TTL", .revision = 0, .family = NFPROTO_IPV4, .target = ttl_tg, .targetsize = sizeof(struct ipt_TTL_info), .table = "mangle", .checkentry = ttl_tg_check, .me = THIS_MODULE, }, { .name = "HL", .revision = 0, .family = NFPROTO_IPV6, .target = hl_tg6, .targetsize = sizeof(struct ip6t_HL_info), .table = "mangle", .checkentry = hl_tg6_check, .me = THIS_MODULE, }, }; static int __init hl_tg_init(void) { return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); } static void __exit hl_tg_exit(void) { xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg)); } module_init(hl_tg_init); module_exit(hl_tg_exit); MODULE_ALIAS("ipt_TTL"); MODULE_ALIAS("ip6t_HL");