1// SPDX-License-Identifier: GPL-2.0-only
2/* Kernel module to match AH parameters. */
3/* (C) 1999-2000 Yon Uriarte <yon@astaro.de>
4 */
5#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
6#include <linux/in.h>
7#include <linux/module.h>
8#include <linux/skbuff.h>
9#include <linux/ip.h>
10
11#include <linux/netfilter_ipv4/ipt_ah.h>
12#include <linux/netfilter/x_tables.h>
13
14MODULE_LICENSE("GPL");
15MODULE_AUTHOR("Yon Uriarte <yon@astaro.de>");
16MODULE_DESCRIPTION("Xtables: IPv4 IPsec-AH SPI match");
17
18/* Returns 1 if the spi is matched by the range, 0 otherwise */
19static inline bool
20spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, bool invert)
21{
22 bool r;
23 pr_debug("spi_match:%c 0x%x <= 0x%x <= 0x%x\n",
24 invert ? '!' : ' ', min, spi, max);
25 r = (spi >= min && spi <= max) ^ invert;
26 pr_debug(" result %s\n", r ? "PASS" : "FAILED");
27 return r;
28}
29
30static bool ah_mt(const struct sk_buff *skb, struct xt_action_param *par)
31{
32 struct ip_auth_hdr _ahdr;
33 const struct ip_auth_hdr *ah;
34 const struct ipt_ah *ahinfo = par->matchinfo;
35
36 /* Must not be a fragment. */
37 if (par->fragoff != 0)
38 return false;
39
40 ah = skb_header_pointer(skb, offset: par->thoff, len: sizeof(_ahdr), buffer: &_ahdr);
41 if (ah == NULL) {
42 /* We've been asked to examine this packet, and we
43 * can't. Hence, no choice but to drop.
44 */
45 pr_debug("Dropping evil AH tinygram.\n");
46 par->hotdrop = true;
47 return false;
48 }
49
50 return spi_match(min: ahinfo->spis[0], max: ahinfo->spis[1],
51 ntohl(ah->spi),
52 invert: !!(ahinfo->invflags & IPT_AH_INV_SPI));
53}
54
55static int ah_mt_check(const struct xt_mtchk_param *par)
56{
57 const struct ipt_ah *ahinfo = par->matchinfo;
58
59 /* Must specify no unknown invflags */
60 if (ahinfo->invflags & ~IPT_AH_INV_MASK) {
61 pr_debug("unknown flags %X\n", ahinfo->invflags);
62 return -EINVAL;
63 }
64 return 0;
65}
66
67static struct xt_match ah_mt_reg __read_mostly = {
68 .name = "ah",
69 .family = NFPROTO_IPV4,
70 .match = ah_mt,
71 .matchsize = sizeof(struct ipt_ah),
72 .proto = IPPROTO_AH,
73 .checkentry = ah_mt_check,
74 .me = THIS_MODULE,
75};
76
77static int __init ah_mt_init(void)
78{
79 return xt_register_match(target: &ah_mt_reg);
80}
81
82static void __exit ah_mt_exit(void)
83{
84 xt_unregister_match(target: &ah_mt_reg);
85}
86
87module_init(ah_mt_init);
88module_exit(ah_mt_exit);
89

source code of linux/net/ipv4/netfilter/ipt_ah.c