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ts3init_linux_netfilter_module
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A Linux netfilter module to aid in (d)dos protection
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ts3init_linux_netfilter_module/src/ts3init_match.c

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/*
* "ts3init" extension for Xtables
*
* Description: A module to aid in ts3 spoof protection
* This is the "match" code
*
* Authors:
* Niels Werensteijn <niels werensteijn [at] teamspeak com>, 2016-10-03
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License; either version 2
* or 3 of the License, as published by the Free Software Foundation.
*/
#include <linux/kernel.h>
#include <linux/version.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/netfilter/x_tables.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>
#include <linux/time.h>
#include <linux/percpu.h>
#include "ts3init_random_seed.h"
#include "ts3init_cookie.h"
#include "ts3init_match.h"
#include "ts3init_header.h"
#include "ts3init_cache.h"
/* Magic number of a TS3INIT packet. */
static const struct ts3_init_header_tag ts3init_header_tag_signature =
{{ .tag8 = {'T', 'S', '3', 'I', 'N', 'I', 'T', '1'} }};
struct ts3_init_checked_client_header_data
{
struct udphdr *udp, udp_buf;
struct ts3_init_client_header* ts3_header, ts3_header_buf;
};
struct ts3_init_checked_server_header_data
{
struct udphdr *udp, udp_buf;
struct ts3_init_server_header* ts3_header, ts3_header_buf;
};
static const int ts3init_payload_sizes[] = { 16, 20, 20, 244, -1, 1 };
/*
* Check that skb contains a valid TS3INIT client header.
* Also initializes header_data, and checks client version.
*/
static bool check_client_header(const struct sk_buff *skb, const struct xt_action_param *par,
struct ts3_init_checked_client_header_data* header_data, __u32 min_client_version)
{
unsigned int data_len;
struct udphdr *udp;
struct ts3_init_client_header* ts3_header;
udp = skb_header_pointer(skb, par->thoff, sizeof(*udp), &header_data->udp_buf);
data_len = be16_to_cpu(udp->len) - sizeof(*udp);
if (data_len < TS3INIT_HEADER_CLIENT_LENGTH)
return false;
ts3_header = (struct ts3_init_client_header*) skb_header_pointer(skb,
par->thoff + sizeof(*udp), TS3INIT_HEADER_CLIENT_LENGTH,
&header_data->ts3_header_buf);
if (!ts3_header) return false;
if (ts3_header->tag.tag64 != ts3init_header_tag_signature.tag64) return false;
if (ts3_header->packet_id != cpu_to_be16(101)) return false;
if (ts3_header->client_id != 0) return false;
if (ts3_header->flags != 0x88) return false;
/* check min_client_version if needed */
if (min_client_version)
{
/* the client version is unaligned in the packet.
* load it byte for byte. big endian*/
__u8* v = ts3_header->client_version;
__u32 packet_min_client_version =
((__u32)v[0]) << 24 | ((__u32)v[1]) << 16 |
((__u32)v[1]) << 8 | ((__u32)v[3]);
if (packet_min_client_version < min_client_version)
return false;
}
header_data->udp = udp;
header_data->ts3_header = ts3_header;
return true;
}
/*
* Check that skb contains a valid TS3INIT server header.
*/
static bool check_server_header(const struct sk_buff *skb, const struct xt_action_param *par,
struct ts3_init_checked_server_header_data* header_data)
{
unsigned int data_len;
struct udphdr *udp;
struct ts3_init_server_header* ts3_header;
udp = skb_header_pointer(skb, par->thoff, sizeof(*udp), &header_data->udp_buf);
data_len = be16_to_cpu(udp->len) - sizeof(*udp);
if (data_len < TS3INIT_HEADER_SERVER_LENGTH) return false;
ts3_header = (struct ts3_init_server_header*) skb_header_pointer(skb,
par->thoff + sizeof(*udp), TS3INIT_HEADER_SERVER_LENGTH,
&header_data->ts3_header_buf);
if (!ts3_header) return false;
if (ts3_header->tag.tag64 != ts3init_header_tag_signature.tag64) return false;
if (ts3_header->packet_id != cpu_to_be16(101)) return false;
if (ts3_header->flags != 0x88) return false;
header_data->udp = udp;
header_data->ts3_header = ts3_header;
return true;
}
static inline __u8* get_payload(const struct sk_buff *skb, const struct xt_action_param *par,
const struct ts3_init_checked_client_header_data* header_data,
__u8 *buf, size_t buf_size)
{
const int header_len = sizeof(*header_data->udp) + TS3INIT_HEADER_CLIENT_LENGTH;
unsigned int data_len = be16_to_cpu(header_data->udp->len) - header_len;
if (data_len < buf_size)
return NULL;
return skb_header_pointer(skb, par->thoff + header_len, buf_size, buf);
}
/*
* Hashes the cookie with source/destination address/port.
*/
static int calculate_cookie(const struct sk_buff *skb, const struct xt_action_param *par,
struct udphdr *udp, __u64 k0, __u64 k1, __u64* out)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 10, 0)
switch (xt_family(par))
#else
switch (par->family)
#endif
{
case NFPROTO_IPV4:
{
const struct iphdr *ip;
ip = ip_hdr(skb);
if (ip == NULL)
{
printk(KERN_ERR KBUILD_MODNAME ": could not load ipv4 addresses\n");
return -EINVAL;
}
return ts3init_calculate_cookie_ipv4(ip, udp, k0, k1, out);
}
case NFPROTO_IPV6:
{
const struct ipv6hdr *ip;
ip = ipv6_hdr(skb);
if (ip == NULL)
{
printk(KERN_ERR KBUILD_MODNAME ": could not load ipv6 addresses\n");
return -EINVAL;
}
return ts3init_calculate_cookie_ipv6(ip, udp, k0, k1, out);
}
default:
printk(KERN_ERR KBUILD_MODNAME ": invalid family\n");
return -EINVAL;
}
}
/*
* The 'ts3init_get_cookie' match handler.
* Checks that the packet is a valid COMMAND_GET_COOKIE.
*/
static bool
ts3init_get_cookie_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_ts3init_get_cookie_mtinfo *info = par->matchinfo;
struct ts3_init_checked_client_header_data header_data;
if (!check_client_header(skb, par, &header_data, info->min_client_version))
return false;
if (header_data.ts3_header->command != COMMAND_GET_COOKIE) return false;
if (info->specific_options & CHK_GET_COOKIE_CHECK_TIMESTAMP)
{
__u8 *payload, payload_buf[ts3init_payload_sizes[COMMAND_GET_COOKIE]];
time_t current_unix_time, packet_unix_time;
payload = get_payload(skb, par, &header_data, payload_buf, sizeof(payload_buf));
if (!payload)
return false;
current_unix_time = ts3init_get_cached_unix_time();
packet_unix_time =
payload[0] << 24 |
payload[1] << 16 |
payload[2] << 8 |
payload[3];
if (abs(current_unix_time - packet_unix_time) > info->max_utc_offset)
return false;
}
return true;
}
/*
* Validates matchinfo recieved from userspace.
*/
static int ts3init_get_cookie_mt_check(const struct xt_mtchk_param *par)
{
struct xt_ts3init_get_cookie_mtinfo *info = par->matchinfo;
if (! (par->family == NFPROTO_IPV4 || par->family == NFPROTO_IPV6))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid protocol (only ipv4 and ipv6) for get_cookie\n");
return -EINVAL;
}
if (info->common_options & ~(CHK_COMMON_VALID_MASK))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid (common) options for get_cookie\n");
return -EINVAL;
}
if (info->specific_options & ~(CHK_GET_COOKIE_VALID_MASK))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid (specific) options for get_cookie\n");
return -EINVAL;
}
return 0;
}
/*
* The 'ts3init_get_cookie' match handler.
* Checks that the packet is a valid COMMAND_GET_PUZZLE, and if the client
* replied with the correct cookie.
*/
static bool ts3init_get_puzzle_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_ts3init_get_puzzle_mtinfo *info = par->matchinfo;
struct ts3_init_checked_client_header_data header_data;
if (!check_client_header(skb, par, &header_data, info->min_client_version))
return false;
if (header_data.ts3_header->command != COMMAND_GET_PUZZLE) return false;
if (info->specific_options & CHK_GET_PUZZLE_CHECK_COOKIE)
{
__u8 *payload, payload_buf[ts3init_payload_sizes[COMMAND_GET_PUZZLE]];
__u64 cookie_seed[2];
__u64 cookie, packet_cookie;
payload = get_payload(skb, par, &header_data, payload_buf, sizeof(payload_buf));
if (!payload)
return false;
if (ts3init_get_cookie_seed_for_packet_index(payload[8], info->random_seed, &cookie_seed) == false)
return false;
/* use cookie_seed and ipaddress and port to create a hash
* (cookie) for this connection */
if (calculate_cookie(skb, par, header_data.udp, cookie_seed[0], cookie_seed[1], &cookie))
return false; /*something went wrong*/
/* compare cookie with payload bytes 0-7. if equal, cookie
* is valid */
packet_cookie = (((u64)((payload)[0])) | ((u64)((payload)[1]) << 8) |
((u64)((payload)[2]) << 16) | ((u64)((payload)[3]) << 24) |
((u64)((payload)[4]) << 32) | ((u64)((payload)[5]) << 40) |
((u64)((payload)[6]) << 48) | ((u64)((payload)[7]) << 56));
if (packet_cookie != cookie) return false;
}
return true;
}
/*
* Validates matchinfo recieved from userspace.
*/
static int ts3init_get_puzzle_mt_check(const struct xt_mtchk_param *par)
{
struct xt_ts3init_get_puzzle_mtinfo *info = par->matchinfo;
if (! (par->family == NFPROTO_IPV4 || par->family == NFPROTO_IPV6))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid protocol (only ipv4 and ipv6) for get_puzzle\n");
return -EINVAL;
}
if (info->common_options & ~(CHK_COMMON_VALID_MASK))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid (common) options for get_puzzle\n");
return -EINVAL;
}
if (info->specific_options & ~(CHK_GET_PUZZLE_VALID_MASK))
{
printk(KERN_INFO KBUILD_MODNAME ": invalid (specific) options for get_puzzle\n");
return -EINVAL;
}
return 0;
}
/*
* The 'ts3init' match handler.
* Checks that the packet is a valid ts3init packet
*/
static bool ts3init_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_ts3init_mtinfo *info = par->matchinfo;
if (info->specific_options & CHK_TS3INIT_CLIENT)
{
struct ts3_init_checked_client_header_data header_data;
if (!check_client_header(skb, par, &header_data, 0))
return false;
if (info->specific_options & CHK_TS3INIT_COMMAND)
{
if (header_data.ts3_header->command != info->command)
return false;
}
}
else if (info->specific_options & CHK_TS3INIT_SERVER)
{
struct ts3_init_checked_server_header_data header_data;
if (!check_server_header(skb, par, &header_data))
return false;
if (info->specific_options & CHK_TS3INIT_COMMAND)
{
if (header_data.ts3_header->command != info->command)
return false;
}
}
else
{
struct udphdr *udp, udp_buf;
u64 *signature, signature_buf;
udp = skb_header_pointer(skb, par->thoff, sizeof(udp_buf), &udp_buf);
if (!udp)
return false;
signature = skb_header_pointer(skb, par->thoff + sizeof(*udp),
sizeof(signature_buf), &signature_buf);
if (!signature || *signature != ts3init_header_tag_signature.tag64)
return false;
}
return true;
}
/*
* Validates matchinfo recieved from userspace.
*/
static int ts3init_check(const struct xt_mtchk_param *par)
{
struct xt_ts3init_get_puzzle_mtinfo *info = par->matchinfo;
if (info->common_options & ~(CHK_COMMON_VALID_MASK))
{
printk(KERN_ERR KBUILD_MODNAME ": invalid (common) options for ts3init\n");
return -EINVAL;
}
if (info->specific_options & ~(CHK_TS3INIT_VALID_MASK))
{
printk(KERN_ERR KBUILD_MODNAME ": invalid (specific) options for ts3init\n");
return -EINVAL;
}
return 0;
}
static struct xt_match ts3init_mt_reg[] __read_mostly =
{
{
.name = "ts3init_get_cookie",
.revision = 0,
.family = NFPROTO_IPV4,
.proto = IPPROTO_UDP,
.matchsize = sizeof(struct xt_ts3init_get_cookie_mtinfo),
.match = ts3init_get_cookie_mt,
.checkentry = ts3init_get_cookie_mt_check,
.me = THIS_MODULE,
},
{
.name = "ts3init_get_cookie",
.revision = 0,
.family = NFPROTO_IPV6,
.proto = IPPROTO_UDP,
.matchsize = sizeof(struct xt_ts3init_get_cookie_mtinfo),
.match = ts3init_get_cookie_mt,
.checkentry = ts3init_get_cookie_mt_check,
.me = THIS_MODULE,
},
{
.name = "ts3init_get_puzzle",
.revision = 0,
.family = NFPROTO_IPV4,
.proto = IPPROTO_UDP,
.matchsize = sizeof(struct xt_ts3init_get_puzzle_mtinfo),
.match = ts3init_get_puzzle_mt,
.checkentry = ts3init_get_puzzle_mt_check,
.me = THIS_MODULE,
},
{
.name = "ts3init_get_puzzle",
.revision = 0,
.family = NFPROTO_IPV6,
.proto = IPPROTO_UDP,
.matchsize = sizeof(struct xt_ts3init_get_puzzle_mtinfo),
.match = ts3init_get_puzzle_mt,
.checkentry = ts3init_get_puzzle_mt_check,
.me = THIS_MODULE,
},
{
.name = "ts3init",
.revision = 0,
.family = NFPROTO_UNSPEC,
.proto = IPPROTO_UDP,
.matchsize = sizeof(struct xt_ts3init_mtinfo),
.match = ts3init_mt,
.checkentry = ts3init_check,
.me = THIS_MODULE,
},
};
int __init ts3init_match_init(void)
{
return xt_register_matches(ts3init_mt_reg, ARRAY_SIZE(ts3init_mt_reg));
}
void ts3init_match_exit(void)
{
xt_unregister_matches(ts3init_mt_reg, ARRAY_SIZE(ts3init_mt_reg));
}