bridge/netfilter/ebt_arpreply.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  ebt_arpreply
0004  *
0005  *  Authors:
0006  *  Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
0007  *  Bart De Schuymer <bdschuym@pandora.be>
0008  *
0009  *  August, 2003
0010  *
0011  */
0012 #include <linux/if_arp.h>
0013 #include <net/arp.h>
0014 #include <linux/module.h>
0015 #include <linux/netfilter/x_tables.h>
0016 #include <linux/netfilter_bridge/ebtables.h>
0017 #include <linux/netfilter_bridge/ebt_arpreply.h>
0018
0019 static unsigned int
0020 ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
0021 {
0022     const struct ebt_arpreply_info *info = par->targinfo;
0023     const __be32 *siptr, *diptr;
0024     __be32 _sip, _dip;
0025     const struct arphdr *ap;
0026     struct arphdr _ah;
0027     const unsigned char *shp;
0028     unsigned char _sha[ETH_ALEN];
0029
0030     ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
0031     if (ap == NULL)
0032         return EBT_DROP;
0033
0034     if (ap->ar_op != htons(ARPOP_REQUEST) ||
0035         ap->ar_hln != ETH_ALEN ||
0036         ap->ar_pro != htons(ETH_P_IP) ||
0037         ap->ar_pln != 4)
0038         return EBT_CONTINUE;
0039
0040     shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
0041     if (shp == NULL)
0042         return EBT_DROP;
0043
0044     siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
0045                    sizeof(_sip), &_sip);
0046     if (siptr == NULL)
0047         return EBT_DROP;
0048
0049     diptr = skb_header_pointer(skb,
0050                    sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
0051                    sizeof(_dip), &_dip);
0052     if (diptr == NULL)
0053         return EBT_DROP;
0054
0055     arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr,
0056          (struct net_device *)xt_in(par),
0057          *diptr, shp, info->mac, shp);
0058
0059     return info->target;
0060 }
0061
0062 static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
0063 {
0064     const struct ebt_arpreply_info *info = par->targinfo;
0065     const struct ebt_entry *e = par->entryinfo;
0066
0067     if (BASE_CHAIN && info->target == EBT_RETURN)
0068         return -EINVAL;
0069     if (e->ethproto != htons(ETH_P_ARP) ||
0070         e->invflags & EBT_IPROTO)
0071         return -EINVAL;
0072     if (ebt_invalid_target(info->target))
0073         return -EINVAL;
0074
0075     return 0;
0076 }
0077
0078 static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
0079     .name       = "arpreply",
0080     .revision   = 0,
0081     .family     = NFPROTO_BRIDGE,
0082     .table      = "nat",
0083     .hooks      = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
0084     .target     = ebt_arpreply_tg,
0085     .checkentry = ebt_arpreply_tg_check,
0086     .targetsize = sizeof(struct ebt_arpreply_info),
0087     .me     = THIS_MODULE,
0088 };
0089
0090 static int __init ebt_arpreply_init(void)
0091 {
0092     return xt_register_target(&ebt_arpreply_tg_reg);
0093 }
0094
0095 static void __exit ebt_arpreply_fini(void)
0096 {
0097     xt_unregister_target(&ebt_arpreply_tg_reg);
0098 }
0099
0100 module_init(ebt_arpreply_init);
0101 module_exit(ebt_arpreply_fini);
0102 MODULE_DESCRIPTION("Ebtables: ARP reply target");
0103 MODULE_LICENSE("GPL");