LXR linux/net/ipv4/netfilter/ipt

   1// SPDX-License-Identifier: GPL-2.0-only
   2/* iptables module for the IPv4 and TCP ECN bits, Version 1.5
   3 *
   4 * (C) 2002 by Harald Welte <laforge@netfilter.org>
   5*/
   6#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   7#include <linux/in.h>
   8#include <linux/module.h>
   9#include <linux/skbuff.h>
  10#include <linux/ip.h>
  11#include <net/ip.h>
  12#include <linux/tcp.h>
  13#include <net/checksum.h>
  14
  15#include <linux/netfilter/x_tables.h>
  16#include <linux/netfilter_ipv4/ip_tables.h>
  17#include <linux/netfilter_ipv4/ipt_ECN.h>
  18
  19MODULE_LICENSE("GPL");
  20MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  21MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
  22
  23/* set ECT codepoint from IP header.
  24 *      return false if there was an error. */
  25static inline bool
  26set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  27{
  28        struct iphdr *iph = ip_hdr(skb);
  29
  30        if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  31                __u8 oldtos;
  32                if (skb_ensure_writable(skb, sizeof(struct iphdr)))
  33                        return false;
  34                iph = ip_hdr(skb);
  35                oldtos = iph->tos;
  36                iph->tos &= ~IPT_ECN_IP_MASK;
  37                iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  38                csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  39        }
  40        return true;
  41}
  42
  43/* Return false if there was an error. */
  44static inline bool
  45set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  46{
  47        struct tcphdr _tcph, *tcph;
  48        __be16 oldval;
  49
  50        /* Not enough header? */
  51        tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  52        if (!tcph)
  53                return false;
  54
  55        if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  56             tcph->ece == einfo->proto.tcp.ece) &&
  57            (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  58             tcph->cwr == einfo->proto.tcp.cwr))
  59                return true;
  60
  61        if (skb_ensure_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
  62                return false;
  63        tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
  64
  65        oldval = ((__be16 *)tcph)[6];
  66        if (einfo->operation & IPT_ECN_OP_SET_ECE)
  67                tcph->ece = einfo->proto.tcp.ece;
  68        if (einfo->operation & IPT_ECN_OP_SET_CWR)
  69                tcph->cwr = einfo->proto.tcp.cwr;
  70
  71        inet_proto_csum_replace2(&tcph->check, skb,
  72                                 oldval, ((__be16 *)tcph)[6], false);
  73        return true;
  74}
  75
  76static unsigned int
  77ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
  78{
  79        const struct ipt_ECN_info *einfo = par->targinfo;
  80
  81        if (einfo->operation & IPT_ECN_OP_SET_IP)
  82                if (!set_ect_ip(skb, einfo))
  83                        return NF_DROP;
  84
  85        if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
  86            ip_hdr(skb)->protocol == IPPROTO_TCP)
  87                if (!set_ect_tcp(skb, einfo))
  88                        return NF_DROP;
  89
  90        return XT_CONTINUE;
  91}
  92
  93static int ecn_tg_check(const struct xt_tgchk_param *par)
  94{
  95        const struct ipt_ECN_info *einfo = par->targinfo;
  96        const struct ipt_entry *e = par->entryinfo;
  97
  98        if (einfo->operation & IPT_ECN_OP_MASK)
  99                return -EINVAL;
 100
 101        if (einfo->ip_ect & ~IPT_ECN_IP_MASK)
 102                return -EINVAL;
 103
 104        if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
 105            (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
 106                pr_info_ratelimited("cannot use operation on non-tcp rule\n");
 107                return -EINVAL;
 108        }
 109        return 0;
 110}
 111
 112static struct xt_target ecn_tg_reg __read_mostly = {
 113        .name           = "ECN",
 114        .family         = NFPROTO_IPV4,
 115        .target         = ecn_tg,
 116        .targetsize     = sizeof(struct ipt_ECN_info),
 117        .table          = "mangle",
 118        .checkentry     = ecn_tg_check,
 119        .me             = THIS_MODULE,
 120};
 121
 122static int __init ecn_tg_init(void)
 123{
 124        return xt_register_target(&ecn_tg_reg);
 125}
 126
 127static void __exit ecn_tg_exit(void)
 128{
 129        xt_unregister_target(&ecn_tg_reg);
 130}
 131
 132module_init(ecn_tg_init);
 133module_exit(ecn_tg_exit);
 134