linux/net/core/secure_seq.c
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   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_key_t net_secret __read_mostly;
  23static siphash_key_t ts_secret __read_mostly;
  24
  25static __always_inline void net_secret_init(void)
  26{
  27        net_get_random_once(&net_secret, sizeof(net_secret));
  28}
  29
  30static __always_inline void ts_secret_init(void)
  31{
  32        net_get_random_once(&ts_secret, sizeof(ts_secret));
  33}
  34#endif
  35
  36#ifdef CONFIG_INET
  37static u32 seq_scale(u32 seq)
  38{
  39        /*
  40         *      As close as possible to RFC 793, which
  41         *      suggests using a 250 kHz clock.
  42         *      Further reading shows this assumes 2 Mb/s networks.
  43         *      For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
  44         *      For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
  45         *      we also need to limit the resolution so that the u32 seq
  46         *      overlaps less than one time per MSL (2 minutes).
  47         *      Choosing a clock of 64 ns period is OK. (period of 274 s)
  48         */
  49        return seq + (ktime_get_real_ns() >> 6);
  50}
  51#endif
  52
  53#if IS_ENABLED(CONFIG_IPV6)
  54u32 secure_tcpv6_ts_off(const struct net *net,
  55                        const __be32 *saddr, const __be32 *daddr)
  56{
  57        const struct {
  58                struct in6_addr saddr;
  59                struct in6_addr daddr;
  60        } __aligned(SIPHASH_ALIGNMENT) combined = {
  61                .saddr = *(struct in6_addr *)saddr,
  62                .daddr = *(struct in6_addr *)daddr,
  63        };
  64
  65        if (net->ipv4.sysctl_tcp_timestamps != 1)
  66                return 0;
  67
  68        ts_secret_init();
  69        return siphash(&combined, offsetofend(typeof(combined), daddr),
  70                       &ts_secret);
  71}
  72EXPORT_SYMBOL(secure_tcpv6_ts_off);
  73
  74u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
  75                     __be16 sport, __be16 dport)
  76{
  77        const struct {
  78                struct in6_addr saddr;
  79                struct in6_addr daddr;
  80                __be16 sport;
  81                __be16 dport;
  82        } __aligned(SIPHASH_ALIGNMENT) combined = {
  83                .saddr = *(struct in6_addr *)saddr,
  84                .daddr = *(struct in6_addr *)daddr,
  85                .sport = sport,
  86                .dport = dport
  87        };
  88        u32 hash;
  89
  90        net_secret_init();
  91        hash = siphash(&combined, offsetofend(typeof(combined), dport),
  92                       &net_secret);
  93        return seq_scale(hash);
  94}
  95EXPORT_SYMBOL(secure_tcpv6_seq);
  96
  97u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
  98                               __be16 dport)
  99{
 100        const struct {
 101                struct in6_addr saddr;
 102                struct in6_addr daddr;
 103                __be16 dport;
 104        } __aligned(SIPHASH_ALIGNMENT) combined = {
 105                .saddr = *(struct in6_addr *)saddr,
 106                .daddr = *(struct in6_addr *)daddr,
 107                .dport = dport
 108        };
 109        net_secret_init();
 110        return siphash(&combined, offsetofend(typeof(combined), dport),
 111                       &net_secret);
 112}
 113EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 114#endif
 115
 116#ifdef CONFIG_INET
 117u32 secure_tcp_ts_off(const struct net *net, __be32 saddr, __be32 daddr)
 118{
 119        if (net->ipv4.sysctl_tcp_timestamps != 1)
 120                return 0;
 121
 122        ts_secret_init();
 123        return siphash_2u32((__force u32)saddr, (__force u32)daddr,
 124                            &ts_secret);
 125}
 126
 127/* secure_tcp_seq_and_tsoff(a, b, 0, d) == secure_ipv4_port_ephemeral(a, b, d),
 128 * but fortunately, `sport' cannot be 0 in any circumstances. If this changes,
 129 * it would be easy enough to have the former function use siphash_4u32, passing
 130 * the arguments as separate u32.
 131 */
 132u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
 133                   __be16 sport, __be16 dport)
 134{
 135        u32 hash;
 136
 137        net_secret_init();
 138        hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,
 139                            (__force u32)sport << 16 | (__force u32)dport,
 140                            &net_secret);
 141        return seq_scale(hash);
 142}
 143EXPORT_SYMBOL_GPL(secure_tcp_seq);
 144
 145u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
 146{
 147        net_secret_init();
 148        return siphash_3u32((__force u32)saddr, (__force u32)daddr,
 149                            (__force u16)dport, &net_secret);
 150}
 151EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
 152#endif
 153
 154#if IS_ENABLED(CONFIG_IP_DCCP)
 155u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
 156                                __be16 sport, __be16 dport)
 157{
 158        u64 seq;
 159        net_secret_init();
 160        seq = siphash_3u32((__force u32)saddr, (__force u32)daddr,
 161                           (__force u32)sport << 16 | (__force u32)dport,
 162                           &net_secret);
 163        seq += ktime_get_real_ns();
 164        seq &= (1ull << 48) - 1;
 165        return seq;
 166}
 167EXPORT_SYMBOL(secure_dccp_sequence_number);
 168
 169#if IS_ENABLED(CONFIG_IPV6)
 170u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
 171                                  __be16 sport, __be16 dport)
 172{
 173        const struct {
 174                struct in6_addr saddr;
 175                struct in6_addr daddr;
 176                __be16 sport;
 177                __be16 dport;
 178        } __aligned(SIPHASH_ALIGNMENT) combined = {
 179                .saddr = *(struct in6_addr *)saddr,
 180                .daddr = *(struct in6_addr *)daddr,
 181                .sport = sport,
 182                .dport = dport
 183        };
 184        u64 seq;
 185        net_secret_init();
 186        seq = siphash(&combined, offsetofend(typeof(combined), dport),
 187                      &net_secret);
 188        seq += ktime_get_real_ns();
 189        seq &= (1ull << 48) - 1;
 190        return seq;
 191}
 192EXPORT_SYMBOL(secure_dccpv6_sequence_number);
 193#endif
 194#endif
 195
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