secure_seq.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  4 */
  5
  6#include <linux/kernel.h>
  7#include <linux/init.h>
  8#include <linux/module.h>
  9#include <linux/cache.h>
 10#include <linux/random.h>
 11#include <linux/hrtimer.h>
 12#include <linux/ktime.h>
 13#include <linux/string.h>
 14#include <linux/net.h>
 15#include <linux/siphash.h>
 16#include <net/secure_seq.h>
 17
 18#if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
 19#include <linux/in6.h>
 20#include <net/tcp.h>
 21
 22static siphash_aligned_key_t net_secret;
 23
 24#define EPHEMERAL_PORT_SHUFFLE_PERIOD (10 * HZ)
 25
 26static __always_inline void net_secret_init(void)
 27{
 28	net_get_random_once(&net_secret, sizeof(net_secret));
 29}
 30#endif
 31
 32#ifdef CONFIG_INET
 33static u32 seq_scale(u32 seq)
 34{
 35	/*
 36	 *	As close as possible to RFC 793, which
 37	 *	suggests using a 250 kHz clock.
 38	 *	Further reading shows this assumes 2 Mb/s networks.
 39	 *	For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
 40	 *	For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
 41	 *	we also need to limit the resolution so that the u32 seq
 42	 *	overlaps less than one time per MSL (2 minutes).
 43	 *	Choosing a clock of 64 ns period is OK. (period of 274 s)
 44	 */
 45	return seq + (ktime_get_real_ns() >> 6);
 46}
 47#endif
 48
 49#if IS_ENABLED(CONFIG_IPV6)
 50union tcp_seq_and_ts_off
 51secure_tcpv6_seq_and_ts_off(const struct net *net, const __be32 *saddr,
 52			    const __be32 *daddr, __be16 sport, __be16 dport)
 53{
 54	const struct {
 55		struct in6_addr saddr;
 56		struct in6_addr daddr;
 57		__be16 sport;
 58		__be16 dport;
 59	} __aligned(SIPHASH_ALIGNMENT) combined = {
 60		.saddr = *(struct in6_addr *)saddr,
 61		.daddr = *(struct in6_addr *)daddr,
 62		.sport = sport,
 63		.dport = dport
 64	};
 65	union tcp_seq_and_ts_off st;
 66
 67	net_secret_init();
 68
 69	st.hash64 = siphash(&combined, offsetofend(typeof(combined), dport),
 70			    &net_secret);
 71
 72	if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
 73		st.ts_off = 0;
 74
 75	st.seq = seq_scale(st.seq);
 76	return st;
 77}
 78EXPORT_SYMBOL(secure_tcpv6_seq_and_ts_off);
 79
 80u64 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
 81			       __be16 dport)
 82{
 83	const struct {
 84		struct in6_addr saddr;
 85		struct in6_addr daddr;
 86		unsigned int timeseed;
 87		__be16 dport;
 88	} __aligned(SIPHASH_ALIGNMENT) combined = {
 89		.saddr = *(struct in6_addr *)saddr,
 90		.daddr = *(struct in6_addr *)daddr,
 91		.timeseed = jiffies / EPHEMERAL_PORT_SHUFFLE_PERIOD,
 92		.dport = dport,
 93	};
 94	net_secret_init();
 95	return siphash(&combined, offsetofend(typeof(combined), dport),
 96		       &net_secret);
 97}
 98EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 99#endif
100
101#ifdef CONFIG_INET
102/* secure_tcp_seq_and_tsoff(a, b, 0, d) == secure_ipv4_port_ephemeral(a, b, d),
103 * but fortunately, `sport' cannot be 0 in any circumstances. If this changes,
104 * it would be easy enough to have the former function use siphash_4u32, passing
105 * the arguments as separate u32.
106 */
107union tcp_seq_and_ts_off
108secure_tcp_seq_and_ts_off(const struct net *net, __be32 saddr, __be32 daddr,
109			  __be16 sport, __be16 dport)
110{
111	u32 ports = (__force u32)sport << 16 | (__force u32)dport;
112	union tcp_seq_and_ts_off st;
113
114	net_secret_init();
115
116	st.hash64 = siphash_3u32((__force u32)saddr, (__force u32)daddr,
117				 ports, &net_secret);
118
119	if (READ_ONCE(net->ipv4.sysctl_tcp_timestamps) != 1)
120		st.ts_off = 0;
121
122	st.seq = seq_scale(st.seq);
123	return st;
124}
125EXPORT_SYMBOL_GPL(secure_tcp_seq_and_ts_off);
126
127u64 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
128{
129	net_secret_init();
130	return siphash_4u32((__force u32)saddr, (__force u32)daddr,
131			    (__force u16)dport,
132			    jiffies / EPHEMERAL_PORT_SHUFFLE_PERIOD,
133			    &net_secret);
134}
135EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
136#endif