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 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 }
  72 EXPORT_SYMBOL(secure_tcpv6_ts_off);
  73
  74 u32 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 }
  95 EXPORT_SYMBOL(secure_tcpv6_seq);
  96
  97 u32 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 }
 113 EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
 114 #endif
 115
 116 #ifdef CONFIG_INET
 117 u32 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  */
 132 u32 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 }
 143
 144 u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
 145 {
 146         net_secret_init();
 147         return siphash_3u32((__force u32)saddr, (__force u32)daddr,
 148                             (__force u16)dport, &net_secret);
 149 }
 150 EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
 151 #endif
 152
 153 #if IS_ENABLED(CONFIG_IP_DCCP)
 154 u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
 155                                 __be16 sport, __be16 dport)
 156 {
 157         u64 seq;
 158         net_secret_init();
 159         seq = siphash_3u32((__force u32)saddr, (__force u32)daddr,
 160                            (__force u32)sport << 16 | (__force u32)dport,
 161                            &net_secret);
 162         seq += ktime_get_real_ns();
 163         seq &= (1ull << 48) - 1;
 164         return seq;
 165 }
 166 EXPORT_SYMBOL(secure_dccp_sequence_number);
 167
 168 #if IS_ENABLED(CONFIG_IPV6)
 169 u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
 170                                   __be16 sport, __be16 dport)
 171 {
 172         const struct {
 173                 struct in6_addr saddr;
 174                 struct in6_addr daddr;
 175                 __be16 sport;
 176                 __be16 dport;
 177         } __aligned(SIPHASH_ALIGNMENT) combined = {
 178                 .saddr = *(struct in6_addr *)saddr,
 179                 .daddr = *(struct in6_addr *)daddr,
 180                 .sport = sport,
 181                 .dport = dport
 182         };
 183         u64 seq;
 184         net_secret_init();
 185         seq = siphash(&combined, offsetofend(typeof(combined), dport),
 186                       &net_secret);
 187         seq += ktime_get_real_ns();
 188         seq &= (1ull << 48) - 1;
 189         return seq;
 190 }
 191 EXPORT_SYMBOL(secure_dccpv6_sequence_number);
 192 #endif
 193 #endif