root/net/ipv4/netfilter/ipt_ECN.c

DEFINITIONS

1. set_ect_ip
2. set_ect_tcp
3. ecn_tg
4. ecn_tg_check
5. ecn_tg_init
6. ecn_tg_exit

   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 
  19 MODULE_LICENSE("GPL");
  20 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  21 MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
  22 
  23 /* set ECT codepoint from IP header.
  24  *      return false if there was an error. */
  25 static inline bool
  26 set_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. */
  44 static inline bool
  45 set_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 
  76 static unsigned int
  77 ecn_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 
  93 static 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 
 112 static 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 
 122 static int __init ecn_tg_init(void)
 123 {
 124         return xt_register_target(&ecn_tg_reg);
 125 }
 126 
 127 static void __exit ecn_tg_exit(void)
 128 {
 129         xt_unregister_target(&ecn_tg_reg);
 130 }
 131 
 132 module_init(ecn_tg_init);
 133 module_exit(ecn_tg_exit);