net/core/secure_seq.c

   1 /*
   2  * Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
   3  */
   4
   5 #include <linux/kernel.h>
   6 #include <linux/init.h>
   7 #include <linux/cryptohash.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
  22 static siphash_key_t net_secret __read_mostly;
  23 static siphash_key_t ts_secret __read_mostly;
  24
  25 static __always_inline void net_secret_init(void)
  26 {
  27         net_get_random_once(&net_secret, sizeof(net_secret));
  28 }
  29
  30 static __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
  37 static 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)
  54 u32 secure_tcpv6_ts_off(const __be32 *saddr, const __be32 *daddr)
  55 {
  56         const struct {
  57                 struct in6_addr saddr;
  58                 struct in6_addr daddr;
  59         } __aligned(SIPHASH_ALIGNMENT) combined = {
  60                 .saddr = *(struct in6_addr *)saddr,
  61                 .daddr = *(struct in6_addr *)daddr,
  62         };
  63
  64         if (sysctl_tcp_timestamps != 1)
  65                 return 0;
  66
  67         ts_secret_init();
  68         return siphash(&combined, offsetofend(typeof(combined), daddr),
  69                        &ts_secret);
  70 }
  71 EXPORT_SYMBOL(secure_tcpv6_ts_off);
  72
  73 u32 secure_tcpv6_seq(const __be32 *saddr, const __be32 *daddr,
  74                      __be16 sport, __be16 dport)
  75 {
  76         const struct {
  77                 struct in6_addr saddr;
  78                 struct in6_addr daddr;
  79                 __be16 sport;
  80                 __be16 dport;
  81         } __aligned(SIPHASH_ALIGNMENT) combined = {
  82                 .saddr = *(struct in6_addr *)saddr,
  83                 .daddr = *(struct in6_addr *)daddr,
  84                 .sport = sport,
  85                 .dport = dport
  86         };
  87         u32 hash;
  88
  89         net_secret_init();
  90         hash = siphash(&combined, offsetofend(typeof(combined), dport),
  91                        &net_secret);
  92         return seq_scale(hash);
  93 }
  94 EXPORT_SYMBOL(secure_tcpv6_seq);
  95
  96 u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
  97                                __be16 dport)
  98 {
  99         const struct {
 100                 struct in6_addr saddr;
 101                 struct in6_addr daddr;
 102                 __be16 dport;
 103         } __aligned(SIPHASH_ALIGNMENT) combined = {
 104                 .saddr = *(struct in6_addr *)saddr,
 105                 .daddr = *(struct in6_addr *)daddr,
 106                 .dport = dport
 107         };
 108         net_secret_init();
 109         return siphash(&combined, offsetofend(typeof(combined), dport),
 110                        &net_secret);
 111 }
 112 EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 113 #endif
 114
 115 #ifdef CONFIG_INET
 116 u32 secure_tcp_ts_off(__be32 saddr, __be32 daddr)
 117 {
 118         if (sysctl_tcp_timestamps != 1)
 119                 return 0;
 120
 121         ts_secret_init();
 122         return siphash_2u32((__force u32)saddr, (__force u32)daddr,
 123                             &ts_secret);
 124 }
 125
 126 /* secure_tcp_seq_and_tsoff(a, b, 0, d) == secure_ipv4_port_ephemeral(a, b, d),
 127  * but fortunately, `sport' cannot be 0 in any circumstances. If this changes,
 128  * it would be easy enough to have the former function use siphash_4u32, passing
 129  * the arguments as separate u32.
 130  */
 131 u32 secure_tcp_seq(__be32 saddr, __be32 daddr,
 132                    __be16 sport, __be16 dport)
 133 {
 134         u32 hash;
 135
 136         net_secret_init();
 137         hash = siphash_3u32((__force u32)saddr, (__force u32)daddr,
 138                             (__force u32)sport << 16 | (__force u32)dport,
 139                             &net_secret);
 140         return seq_scale(hash);
 141 }
 142
 143 u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
 144 {
 145         net_secret_init();
 146         return siphash_3u32((__force u32)saddr, (__force u32)daddr,
 147                             (__force u16)dport, &net_secret);
 148 }
 149 EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
 150 #endif
 151
 152 #if IS_ENABLED(CONFIG_IP_DCCP)
 153 u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
 154                                 __be16 sport, __be16 dport)
 155 {
 156         u64 seq;
 157         net_secret_init();
 158         seq = siphash_3u32((__force u32)saddr, (__force u32)daddr,
 159                            (__force u32)sport << 16 | (__force u32)dport,
 160                            &net_secret);
 161         seq += ktime_get_real_ns();
 162         seq &= (1ull << 48) - 1;
 163         return seq;
 164 }
 165 EXPORT_SYMBOL(secure_dccp_sequence_number);
 166
 167 #if IS_ENABLED(CONFIG_IPV6)
 168 u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
 169                                   __be16 sport, __be16 dport)
 170 {
 171         const struct {
 172                 struct in6_addr saddr;
 173                 struct in6_addr daddr;
 174                 __be16 sport;
 175                 __be16 dport;
 176         } __aligned(SIPHASH_ALIGNMENT) combined = {
 177                 .saddr = *(struct in6_addr *)saddr,
 178                 .daddr = *(struct in6_addr *)daddr,
 179                 .sport = sport,
 180                 .dport = dport
 181         };
 182         u64 seq;
 183         net_secret_init();
 184         seq = siphash(&combined, offsetofend(typeof(combined), dport),
 185                       &net_secret);
 186         seq += ktime_get_real_ns();
 187         seq &= (1ull << 48) - 1;
 188         return seq;
 189 }
 190 EXPORT_SYMBOL(secure_dccpv6_sequence_number);
 191 #endif
 192 #endif