client/jansson/hashtable_seed.c

   1 /* Generate sizeof(uint32_t) bytes of as random data as possible to seed
   2    the hash function.
   3 */
   4
   5 #ifdef HAVE_CONFIG_H
   6 #include <jansson_private_config.h>
   7 #endif
   8
   9 #include <stdio.h>
  10 #include <time.h>
  11
  12 #ifdef HAVE_STDINT_H
  13 #include <stdint.h>
  14 #endif
  15
  16 #ifdef HAVE_FCNTL_H
  17 #include <fcntl.h>
  18 #endif
  19
  20 #ifdef HAVE_SCHED_H
  21 #include <sched.h>
  22 #endif
  23
  24 #ifdef HAVE_UNISTD_H
  25 #include <unistd.h>
  26 #endif
  27
  28 #ifdef HAVE_SYS_STAT_H
  29 #include <sys/stat.h>
  30 #endif
  31
  32 #ifdef HAVE_SYS_TIME_H
  33 #include <sys/time.h>
  34 #endif
  35
  36 #ifdef HAVE_SYS_TYPES_H
  37 #include <sys/types.h>
  38 #endif
  39
  40 #if defined(_WIN32)
  41 /* For GetModuleHandle(), GetProcAddress() and GetCurrentProcessId() */
  42 #include <windows.h>
  43 #endif
  44
  45 #include "jansson.h"
  46
  47
  48 static uint32_t buf_to_uint32(char *data) {
  49     size_t i;
  50     uint32_t result = 0;
  51
  52     for (i = 0; i < sizeof(uint32_t); i++)
  53         result = (result << 8) | (unsigned char)data[i];
  54
  55     return result;
  56 }
  57
  58
  59
  60 /* /dev/urandom */
  61 #if !defined(_WIN32) && defined(USE_URANDOM)
  62 static int seed_from_urandom(uint32_t *seed) {
  63     /* Use unbuffered I/O if we have open(), close() and read(). Otherwise
  64        fall back to fopen() */
  65
  66     char data[sizeof(uint32_t)];
  67     int ok;
  68
  69 #if defined(HAVE_OPEN) && defined(HAVE_CLOSE) && defined(HAVE_READ)
  70     int urandom;
  71     urandom = open("/dev/urandom", O_RDONLY);
  72     if (urandom == -1)
  73         return 1;
  74
  75     ok = read(urandom, data, sizeof(uint32_t)) == sizeof(uint32_t);
  76     close(urandom);
  77 #else
  78     FILE *urandom;
  79
  80     urandom = fopen("/dev/urandom", "rb");
  81     if (!urandom)
  82         return 1;
  83
  84     ok = fread(data, 1, sizeof(uint32_t), urandom) == sizeof(uint32_t);
  85     fclose(urandom);
  86 #endif
  87
  88     if (!ok)
  89         return 1;
  90
  91     *seed = buf_to_uint32(data);
  92     return 0;
  93 }
  94 #endif
  95
  96 /* Windows Crypto API */
  97 #if defined(_WIN32) && defined(USE_WINDOWS_CRYPTOAPI)
  98 #include <wincrypt.h>
  99
 100 typedef BOOL (WINAPI *CRYPTACQUIRECONTEXTA)(HCRYPTPROV *phProv, LPCSTR pszContainer, LPCSTR pszProvider, DWORD dwProvType, DWORD dwFlags);
 101 typedef BOOL (WINAPI *CRYPTGENRANDOM)(HCRYPTPROV hProv, DWORD dwLen, BYTE *pbBuffer);
 102 typedef BOOL (WINAPI *CRYPTRELEASECONTEXT)(HCRYPTPROV hProv, DWORD dwFlags);
 103
 104 static int seed_from_windows_cryptoapi(uint32_t *seed)
 105 {
 106     HINSTANCE hAdvAPI32 = NULL;
 107     CRYPTACQUIRECONTEXTA pCryptAcquireContext = NULL;
 108     CRYPTGENRANDOM pCryptGenRandom = NULL;
 109     CRYPTRELEASECONTEXT pCryptReleaseContext = NULL;
 110     HCRYPTPROV hCryptProv = 0;
 111     BYTE data[sizeof(uint32_t)];
 112     int ok;
 113
 114     hAdvAPI32 = GetModuleHandle(TEXT("advapi32.dll"));
 115     if(hAdvAPI32 == NULL)
 116         return 1;
 117
 118     pCryptAcquireContext = (CRYPTACQUIRECONTEXTA)GetProcAddress(hAdvAPI32, "CryptAcquireContextA");
 119     if (!pCryptAcquireContext)
 120         return 1;
 121
 122     pCryptGenRandom = (CRYPTGENRANDOM)GetProcAddress(hAdvAPI32, "CryptGenRandom");
 123     if (!pCryptGenRandom)
 124         return 1;
 125
 126     pCryptReleaseContext = (CRYPTRELEASECONTEXT)GetProcAddress(hAdvAPI32, "CryptReleaseContext");
 127     if (!pCryptReleaseContext)
 128         return 1;
 129
 130     if (!pCryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT))
 131         return 1;
 132
 133     ok = pCryptGenRandom(hCryptProv, sizeof(uint32_t), data);
 134     pCryptReleaseContext(hCryptProv, 0);
 135
 136     if (!ok)
 137         return 1;
 138
 139     *seed = buf_to_uint32((char *)data);
 140     return 0;
 141 }
 142 #endif
 143
 144 /* gettimeofday() and getpid() */
 145 static int seed_from_timestamp_and_pid(uint32_t *seed) {
 146 #ifdef HAVE_GETTIMEOFDAY
 147     /* XOR of seconds and microseconds */
 148     struct timeval tv;
 149     gettimeofday(&tv, NULL);
 150     *seed = (uint32_t)tv.tv_sec ^ (uint32_t)tv.tv_usec;
 151 #else
 152     /* Seconds only */
 153     *seed = (uint32_t)time(NULL);
 154 #endif
 155
 156     /* XOR with PID for more randomness */
 157 #if defined(_WIN32)
 158     *seed ^= (uint32_t)GetCurrentProcessId();
 159 #elif defined(HAVE_GETPID)
 160     *seed ^= (uint32_t)getpid();
 161 #endif
 162
 163     return 0;
 164 }
 165
 166 static uint32_t generate_seed() {
 167     uint32_t seed = 0;
 168     int done = 0;
 169
 170 #if !defined(_WIN32) && defined(USE_URANDOM)
 171     if (seed_from_urandom(&seed) == 0)
 172         done = 1;
 173 #endif
 174
 175 #if defined(_WIN32) && defined(USE_WINDOWS_CRYPTOAPI)
 176     if (seed_from_windows_cryptoapi(&seed) == 0)
 177         done = 1;
 178 #endif
 179
 180     if (!done) {
 181         /* Fall back to timestamp and PID if no better randomness is
 182            available */
 183         seed_from_timestamp_and_pid(&seed);
 184     }
 185
 186     /* Make sure the seed is never zero */
 187     if (seed == 0)
 188         seed = 1;
 189
 190     return seed;
 191 }
 192
 193
 194 volatile uint32_t hashtable_seed = 0;
 195
 196 #if defined(HAVE_ATOMIC_BUILTINS) && (defined(HAVE_SCHED_YIELD) || !defined(_WIN32))
 197 static volatile char seed_initialized = 0;
 198
 199 void json_object_seed(size_t seed) {
 200     uint32_t new_seed = (uint32_t)seed;
 201
 202     if (hashtable_seed == 0) {
 203         if (__atomic_test_and_set(&seed_initialized, __ATOMIC_RELAXED) == 0) {
 204             /* Do the seeding ourselves */
 205             if (new_seed == 0)
 206                 new_seed = generate_seed();
 207
 208             __atomic_store_n(&hashtable_seed, new_seed, __ATOMIC_RELEASE);
 209         } else {
 210             /* Wait for another thread to do the seeding */
 211             do {
 212 #ifdef HAVE_SCHED_YIELD
 213                 sched_yield();
 214 #endif
 215             } while(__atomic_load_n(&hashtable_seed, __ATOMIC_ACQUIRE) == 0);
 216         }
 217     }
 218 }
 219 #elif defined(HAVE_SYNC_BUILTINS) && (defined(HAVE_SCHED_YIELD) || !defined(_WIN32))
 220 void json_object_seed(size_t seed) {
 221     uint32_t new_seed = (uint32_t)seed;
 222
 223     if (hashtable_seed == 0) {
 224         if (new_seed == 0) {
 225             /* Explicit synchronization fences are not supported by the
 226                __sync builtins, so every thread getting here has to
 227                generate the seed value.
 228             */
 229             new_seed = generate_seed();
 230         }
 231
 232         do {
 233             if (__sync_bool_compare_and_swap(&hashtable_seed, 0, new_seed)) {
 234                 /* We were the first to seed */
 235                 break;
 236             } else {
 237                 /* Wait for another thread to do the seeding */
 238 #ifdef HAVE_SCHED_YIELD
 239                 sched_yield();
 240 #endif
 241             }
 242         } while(hashtable_seed == 0);
 243     }
 244 }
 245 #elif defined(_WIN32)
 246 static long seed_initialized = 0;
 247 void json_object_seed(size_t seed) {
 248     uint32_t new_seed = (uint32_t)seed;
 249
 250     if (hashtable_seed == 0) {
 251         if (InterlockedIncrement(&seed_initialized) == 1) {
 252             /* Do the seeding ourselves */
 253             if (new_seed == 0)
 254                 new_seed = generate_seed();
 255
 256             hashtable_seed = new_seed;
 257         } else {
 258             /* Wait for another thread to do the seeding */
 259             do {
 260                 SwitchToThread();
 261             } while (hashtable_seed == 0);
 262         }
 263     }
 264 }
 265 #else
 266 /* Fall back to a thread-unsafe version */
 267 void json_object_seed(size_t seed) {
 268     uint32_t new_seed = (uint32_t)seed;
 269
 270     if (hashtable_seed == 0) {
 271         if (new_seed == 0)
 272             new_seed = generate_seed();
 273
 274         hashtable_seed = new_seed;
 275     }
 276 }
 277 #endif