cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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xt_tcpmss.c (2459B)

      1// SPDX-License-Identifier: GPL-2.0-only
      2/* Kernel module to match TCP MSS values. */
      3
      4/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
      5 * Portions (C) 2005 by Harald Welte <laforge@netfilter.org>
      6 */
      7
      8#include <linux/module.h>
      9#include <linux/skbuff.h>
     10#include <net/tcp.h>
     11
     12#include <linux/netfilter/xt_tcpmss.h>
     13#include <linux/netfilter/x_tables.h>
     14
     15#include <linux/netfilter_ipv4/ip_tables.h>
     16#include <linux/netfilter_ipv6/ip6_tables.h>
     17
     18MODULE_LICENSE("GPL");
     19MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
     20MODULE_DESCRIPTION("Xtables: TCP MSS match");
     21MODULE_ALIAS("ipt_tcpmss");
     22MODULE_ALIAS("ip6t_tcpmss");
     23
     24static bool
     25tcpmss_mt(const struct sk_buff *skb, struct xt_action_param *par)
     26{
     27	const struct xt_tcpmss_match_info *info = par->matchinfo;
     28	const struct tcphdr *th;
     29	struct tcphdr _tcph;
     30	/* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
     31	const u_int8_t *op;
     32	u8 _opt[15 * 4 - sizeof(_tcph)];
     33	unsigned int i, optlen;
     34
     35	/* If we don't have the whole header, drop packet. */
     36	th = skb_header_pointer(skb, par->thoff, sizeof(_tcph), &_tcph);
     37	if (th == NULL)
     38		goto dropit;
     39
     40	/* Malformed. */
     41	if (th->doff*4 < sizeof(*th))
     42		goto dropit;
     43
     44	optlen = th->doff*4 - sizeof(*th);
     45	if (!optlen)
     46		goto out;
     47
     48	/* Truncated options. */
     49	op = skb_header_pointer(skb, par->thoff + sizeof(*th), optlen, _opt);
     50	if (op == NULL)
     51		goto dropit;
     52
     53	for (i = 0; i < optlen; ) {
     54		if (op[i] == TCPOPT_MSS
     55		    && (optlen - i) >= TCPOLEN_MSS
     56		    && op[i+1] == TCPOLEN_MSS) {
     57			u_int16_t mssval;
     58
     59			mssval = (op[i+2] << 8) | op[i+3];
     60
     61			return (mssval >= info->mss_min &&
     62				mssval <= info->mss_max) ^ info->invert;
     63		}
     64		if (op[i] < 2)
     65			i++;
     66		else
     67			i += op[i+1] ? : 1;
     68	}
     69out:
     70	return info->invert;
     71
     72dropit:
     73	par->hotdrop = true;
     74	return false;
     75}
     76
     77static struct xt_match tcpmss_mt_reg[] __read_mostly = {
     78	{
     79		.name		= "tcpmss",
     80		.family		= NFPROTO_IPV4,
     81		.match		= tcpmss_mt,
     82		.matchsize	= sizeof(struct xt_tcpmss_match_info),
     83		.proto		= IPPROTO_TCP,
     84		.me		= THIS_MODULE,
     85	},
     86	{
     87		.name		= "tcpmss",
     88		.family		= NFPROTO_IPV6,
     89		.match		= tcpmss_mt,
     90		.matchsize	= sizeof(struct xt_tcpmss_match_info),
     91		.proto		= IPPROTO_TCP,
     92		.me		= THIS_MODULE,
     93	},
     94};
     95
     96static int __init tcpmss_mt_init(void)
     97{
     98	return xt_register_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
     99}
    100
    101static void __exit tcpmss_mt_exit(void)
    102{
    103	xt_unregister_matches(tcpmss_mt_reg, ARRAY_SIZE(tcpmss_mt_reg));
    104}
    105
    106module_init(tcpmss_mt_init);
    107module_exit(tcpmss_mt_exit);