// SPDX-License-Identifier: GPL-2.0-only
/* Kernel module to match L2TP header parameters. */
/* (C) 2013 James Chapman <[email protected]>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/if_ether.h>
#include <net/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/udp.h>
#include <linux/l2tp.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter/xt_l2tp.h>
/* L2TP header masks */
#define L2TP_HDR_T_BIT 0x8000
#define L2TP_HDR_L_BIT 0x4000
#define L2TP_HDR_VER 0x000f
MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Chapman <[email protected]>");
MODULE_DESCRIPTION("Xtables: L2TP header match");
MODULE_ALIAS("ipt_l2tp");
MODULE_ALIAS("ip6t_l2tp");
/* The L2TP fields that can be matched */
struct l2tp_data {
u32 tid;
u32 sid;
u8 type;
u8 version;
};
union l2tp_val {
__be16 val16[2];
__be32 val32;
};
static bool l2tp_match(const struct xt_l2tp_info *info, struct l2tp_data *data)
{
if ((info->flags & XT_L2TP_TYPE) && (info->type != data->type))
return false;
if ((info->flags & XT_L2TP_VERSION) && (info->version != data->version))
return false;
/* Check tid only for L2TPv3 control or any L2TPv2 packets */
if ((info->flags & XT_L2TP_TID) &&
((data->type == XT_L2TP_TYPE_CONTROL) || (data->version == 2)) &&
(info->tid != data->tid))
return false;
/* Check sid only for L2TP data packets */
if ((info->flags & XT_L2TP_SID) && (data->type == XT_L2TP_TYPE_DATA) &&
(info->sid != data->sid))
return false;
return true;
}
/* Parse L2TP header fields when UDP encapsulation is used. Handles
* L2TPv2 and L2TPv3. Note the L2TPv3 control and data packets have a
* different format. See
* RFC2661, Section 3.1, L2TPv2 Header Format
* RFC3931, Section 3.2.1, L2TPv3 Control Message Header
* RFC3931, Section 3.2.2, L2TPv3 Data Message Header
* RFC3931, Section 4.1.2.1, L2TPv3 Session Header over UDP
*/
static bool l2tp_udp_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff)
{
const struct xt_l2tp_info *info = par->matchinfo;
int uhlen = sizeof(struct udphdr);
int offs = thoff + uhlen;
union l2tp_val *lh;
union l2tp_val lhbuf;
u16 flags;
struct l2tp_data data = { 0, };
if (par->fragoff != 0)
return false;
/* Extract L2TP header fields. The flags in the first 16 bits
* tell us where the other fields are.
*/
lh = skb_header_pointer(skb, offs, 2, &lhbuf);
if (lh == NULL)
return false;
flags = ntohs(lh->val16[0]);
if (flags & L2TP_HDR_T_BIT)
data.type = XT_L2TP_TYPE_CONTROL;
else
data.type = XT_L2TP_TYPE_DATA;
data.version = (u8) flags & L2TP_HDR_VER;
/* Now extract the L2TP tid/sid. These are in different places
* for L2TPv2 (rfc2661) and L2TPv3 (rfc3931). For L2TPv2, we
* must also check to see if the length field is present,
* since this affects the offsets into the packet of the
* tid/sid fields.
*/
if (data.version == 3) {
lh = skb_header_pointer(skb, offs + 4, 4, &lhbuf);
if (lh == NULL)
return false;
if (data.type == XT_L2TP_TYPE_CONTROL)
data.tid = ntohl(lh->val32);
else
data.sid = ntohl(lh->val32);
} else if (data.version == 2) {
if (flags & L2TP_HDR_L_BIT)
offs += 2;
lh = skb_header_pointer(skb, offs + 2, 4, &lhbuf);
if (lh == NULL)
return false;
data.tid = (u32) ntohs(lh->val16[0]);
data.sid = (u32) ntohs(lh->val16[1]);
} else
return false;
return l2tp_match(info, &data);
}
/* Parse L2TP header fields for IP encapsulation (no UDP header).
* L2TPv3 data packets have a different form with IP encap. See
* RC3931, Section 4.1.1.1, L2TPv3 Session Header over IP.
* RC3931, Section 4.1.1.2, L2TPv3 Control and Data Traffic over IP.
*/
static bool l2tp_ip_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff)
{
const struct xt_l2tp_info *info = par->matchinfo;
union l2tp_val *lh;
union l2tp_val lhbuf;
struct l2tp_data data = { 0, };
/* For IP encap, the L2TP sid is the first 32-bits. */
lh = skb_header_pointer(skb, thoff, sizeof(lhbuf), &lhbuf);
if (lh == NULL)
return false;
if (lh->val32 == 0) {
/* Must be a control packet. The L2TP tid is further
* into the packet.
*/
data.type = XT_L2TP_TYPE_CONTROL;
lh = skb_header_pointer(skb, thoff + 8, sizeof(lhbuf),
&lhbuf);
if (lh == NULL)
return false;
data.tid = ntohl(lh->val32);
} else {
data.sid = ntohl(lh->val32);
data.type = XT_L2TP_TYPE_DATA;
}
data.version = 3;
return l2tp_match(info, &data);
}
static bool l2tp_mt4(const struct sk_buff *skb, struct xt_action_param *par)
{
struct iphdr *iph = ip_hdr(skb);
u8 ipproto = iph->protocol;
/* l2tp_mt_check4 already restricts the transport protocol */
switch (ipproto) {
case IPPROTO_UDP:
return l2tp_udp_mt(skb, par, par->thoff);
case IPPROTO_L2TP:
return l2tp_ip_mt(skb, par, par->thoff);
}
return false;
}
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static bool l2tp_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
unsigned int thoff = 0;
unsigned short fragoff = 0;
int ipproto;
ipproto = ipv6_find_hdr(skb, &thoff, -1, &fragoff, NULL);
if (fragoff != 0)
return false;
/* l2tp_mt_check6 already restricts the transport protocol */
switch (ipproto) {
case IPPROTO_UDP:
return l2tp_udp_mt(skb, par, thoff);
case IPPROTO_L2TP:
return l2tp_ip_mt(skb, par, thoff);
}
return false;
}
#endif
static int l2tp_mt_check(const struct xt_mtchk_param *par)
{
const struct xt_l2tp_info *info = par->matchinfo;
/* Check for invalid flags */
if (info->flags & ~(XT_L2TP_TID | XT_L2TP_SID | XT_L2TP_VERSION |
XT_L2TP_TYPE)) {
pr_info_ratelimited("unknown flags: %x\n", info->flags);
return -EINVAL;
}
/* At least one of tid, sid or type=control must be specified */
if ((!(info->flags & XT_L2TP_TID)) &&
(!(info->flags & XT_L2TP_SID)) &&
((!(info->flags & XT_L2TP_TYPE)) ||
(info->type != XT_L2TP_TYPE_CONTROL))) {
pr_info_ratelimited("invalid flags combination: %x\n",
info->flags);
return -EINVAL;
}
/* If version 2 is specified, check that incompatible params
* are not supplied
*/
if (info->flags & XT_L2TP_VERSION) {
if ((info->version < 2) || (info->version > 3)) {
pr_info_ratelimited("wrong L2TP version: %u\n",
info->version);
return -EINVAL;
}
if (info->version == 2) {
if ((info->flags & XT_L2TP_TID) &&
(info->tid > 0xffff)) {
pr_info_ratelimited("v2 tid > 0xffff: %u\n",
info->tid);
return -EINVAL;
}
if ((info->flags & XT_L2TP_SID) &&
(info->sid > 0xffff)) {
pr_info_ratelimited("v2 sid > 0xffff: %u\n",
info->sid);
return -EINVAL;
}
}
}
return 0;
}
static int l2tp_mt_check4(const struct xt_mtchk_param *par)
{
const struct xt_l2tp_info *info = par->matchinfo;
const struct ipt_entry *e = par->entryinfo;
const struct ipt_ip *ip = &e->ip;
int ret;
ret = l2tp_mt_check(par);
if (ret != 0)
return ret;
if ((ip->proto != IPPROTO_UDP) &&
(ip->proto != IPPROTO_L2TP)) {
pr_info_ratelimited("missing protocol rule (udp|l2tpip)\n");
return -EINVAL;
}
if ((ip->proto == IPPROTO_L2TP) &&
(info->version == 2)) {
pr_info_ratelimited("v2 doesn't support IP mode\n");
return -EINVAL;
}
return 0;
}
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static int l2tp_mt_check6(const struct xt_mtchk_param *par)
{
const struct xt_l2tp_info *info = par->matchinfo;
const struct ip6t_entry *e = par->entryinfo;
const struct ip6t_ip6 *ip = &e->ipv6;
int ret;
ret = l2tp_mt_check(par);
if (ret != 0)
return ret;
if ((ip->proto != IPPROTO_UDP) &&
(ip->proto != IPPROTO_L2TP)) {
pr_info_ratelimited("missing protocol rule (udp|l2tpip)\n");
return -EINVAL;
}
if ((ip->proto == IPPROTO_L2TP) &&
(info->version == 2)) {
pr_info_ratelimited("v2 doesn't support IP mode\n");
return -EINVAL;
}
return 0;
}
#endif
static struct xt_match l2tp_mt_reg[] __read_mostly = {
{
.name = "l2tp",
.revision = 0,
.family = NFPROTO_IPV4,
.match = l2tp_mt4,
.matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)),
.checkentry = l2tp_mt_check4,
.hooks = ((1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN) |
(1 << NF_INET_LOCAL_OUT) |
(1 << NF_INET_FORWARD)),
.me = THIS_MODULE,
},
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
{
.name = "l2tp",
.revision = 0,
.family = NFPROTO_IPV6,
.match = l2tp_mt6,
.matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)),
.checkentry = l2tp_mt_check6,
.hooks = ((1 << NF_INET_PRE_ROUTING) |
(1 << NF_INET_LOCAL_IN) |
(1 << NF_INET_LOCAL_OUT) |
(1 << NF_INET_FORWARD)),
.me = THIS_MODULE,
},
#endif
};
static int __init l2tp_mt_init(void)
{
return xt_register_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg));
}
static void __exit l2tp_mt_exit(void)
{
xt_unregister_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg));
}
module_init(l2tp_mt_init);
module_exit(l2tp_mt_exit);
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