// SPDX-License-Identifier: GPL-2.0-only
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/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
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*
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* (C) 2002 by Harald Welte <laforge@netfilter.org>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/in.h>
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <net/ip.h>
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#include <linux/tcp.h>
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#include <net/checksum.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#include <linux/netfilter_ipv4/ipt_ECN.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
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MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
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/* set ECT codepoint from IP header.
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* return false if there was an error. */
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static inline bool
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set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
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{
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struct iphdr *iph = ip_hdr(skb);
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if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
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__u8 oldtos;
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if (skb_ensure_writable(skb, sizeof(struct iphdr)))
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return false;
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iph = ip_hdr(skb);
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oldtos = iph->tos;
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iph->tos &= ~IPT_ECN_IP_MASK;
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iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
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csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
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}
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return true;
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}
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/* Return false if there was an error. */
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static inline bool
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set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
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{
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struct tcphdr _tcph, *tcph;
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__be16 oldval;
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/* Not enough header? */
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tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
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if (!tcph)
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return false;
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if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
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tcph->ece == einfo->proto.tcp.ece) &&
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(!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
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tcph->cwr == einfo->proto.tcp.cwr))
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return true;
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if (skb_ensure_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
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return false;
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tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
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oldval = ((__be16 *)tcph)[6];
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if (einfo->operation & IPT_ECN_OP_SET_ECE)
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tcph->ece = einfo->proto.tcp.ece;
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if (einfo->operation & IPT_ECN_OP_SET_CWR)
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tcph->cwr = einfo->proto.tcp.cwr;
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inet_proto_csum_replace2(&tcph->check, skb,
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oldval, ((__be16 *)tcph)[6], false);
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return true;
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}
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static unsigned int
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ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
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{
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const struct ipt_ECN_info *einfo = par->targinfo;
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if (einfo->operation & IPT_ECN_OP_SET_IP)
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if (!set_ect_ip(skb, einfo))
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return NF_DROP;
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if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
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ip_hdr(skb)->protocol == IPPROTO_TCP)
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if (!set_ect_tcp(skb, einfo))
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return NF_DROP;
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return XT_CONTINUE;
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}
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static int ecn_tg_check(const struct xt_tgchk_param *par)
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{
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const struct ipt_ECN_info *einfo = par->targinfo;
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const struct ipt_entry *e = par->entryinfo;
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if (einfo->operation & IPT_ECN_OP_MASK)
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return -EINVAL;
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if (einfo->ip_ect & ~IPT_ECN_IP_MASK)
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return -EINVAL;
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if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
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(e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
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pr_info_ratelimited("cannot use operation on non-tcp rule\n");
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return -EINVAL;
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}
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return 0;
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}
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static struct xt_target ecn_tg_reg __read_mostly = {
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.name = "ECN",
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.family = NFPROTO_IPV4,
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.target = ecn_tg,
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.targetsize = sizeof(struct ipt_ECN_info),
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.table = "mangle",
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.checkentry = ecn_tg_check,
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.me = THIS_MODULE,
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};
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static int __init ecn_tg_init(void)
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{
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return xt_register_target(&ecn_tg_reg);
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}
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static void __exit ecn_tg_exit(void)
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{
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xt_unregister_target(&ecn_tg_reg);
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}
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module_init(ecn_tg_init);
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module_exit(ecn_tg_exit);
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