diff options
Diffstat (limited to 'src/hashtable_seed.c')
| -rw-r--r-- | src/hashtable_seed.c | 278 |
1 files changed, 278 insertions, 0 deletions
diff --git a/src/hashtable_seed.c b/src/hashtable_seed.c new file mode 100644 index 0000000..1789b07 --- /dev/null +++ b/src/hashtable_seed.c @@ -0,0 +1,278 @@ +/* Generate sizeof(uint32_t) bytes of as random data as possible to seed + the hash function. +*/ + +#ifdef HAVE_CONFIG_H +#include <jansson_private_config.h> +#endif + +#include <stdio.h> +#include <time.h> + +#ifdef HAVE_STDINT_H +#include <stdint.h> +#endif + +#ifdef HAVE_FCNTL_H +#include <fcntl.h> +#endif + +#ifdef HAVE_SCHED_H +#include <sched.h> +#endif + +#ifdef HAVE_UNISTD_H +#include <unistd.h> +#endif + +#ifdef HAVE_SYS_STAT_H +#include <sys/stat.h> +#endif + +#ifdef HAVE_SYS_TIME_H +#include <sys/time.h> +#endif + +#ifdef HAVE_SYS_TYPES_H +#include <sys/types.h> +#endif + +#if defined(_WIN32) +/* For _getpid() */ +#include <process.h> +#endif + +#include "jansson.h" + + +static uint32_t buf_to_uint32(char *data) { + size_t i; + uint32_t result = 0; + + for (i = 0; i < sizeof(uint32_t); i++) + result = (result << 8) | (unsigned char)data[i]; + + return result; +} + + + +/* /dev/urandom */ +#if !defined(_WIN32) && defined(USE_URANDOM) +static int seed_from_urandom(uint32_t *seed) { + /* Use unbuffered I/O if we have open(), close() and read(). Otherwise + fall back to fopen() */ + + char data[sizeof(uint32_t)]; + int ok; + +#if defined(HAVE_OPEN) && defined(HAVE_CLOSE) && defined(HAVE_READ) + int urandom; + urandom = open("/dev/urandom", O_RDONLY); + if (urandom == -1) + return 1; + + ok = read(urandom, data, sizeof(uint32_t)) == sizeof(uint32_t); + close(urandom); +#else + FILE *urandom; + + urandom = fopen("/dev/urandom", "rb"); + if (!urandom) + return 1; + + ok = fread(data, 1, sizeof(uint32_t), urandom) == sizeof(uint32_t); + fclose(urandom); +#endif + + if (!ok) + return 1; + + *seed = buf_to_uint32(data); + return 0; +} +#endif + +/* Windows Crypto API */ +#if defined(_WIN32) && defined(USE_WINDOWS_CRYPTOAPI) +#include <windows.h> +#include <wincrypt.h> + +typedef BOOL (WINAPI *CRYPTACQUIRECONTEXTA)(HCRYPTPROV *phProv, LPCSTR pszContainer, LPCSTR pszProvider, DWORD dwProvType, DWORD dwFlags); +typedef BOOL (WINAPI *CRYPTGENRANDOM)(HCRYPTPROV hProv, DWORD dwLen, BYTE *pbBuffer); +typedef BOOL (WINAPI *CRYPTRELEASECONTEXT)(HCRYPTPROV hProv, DWORD dwFlags); + +static int seed_from_windows_cryptoapi(uint32_t *seed) +{ + HINSTANCE hAdvAPI32 = NULL; + CRYPTACQUIRECONTEXTA pCryptAcquireContext = NULL; + CRYPTGENRANDOM pCryptGenRandom = NULL; + CRYPTRELEASECONTEXT pCryptReleaseContext = NULL; + HCRYPTPROV hCryptProv = 0; + BYTE data[sizeof(uint32_t)]; + int ok; + + hAdvAPI32 = GetModuleHandle("advapi32.dll"); + if(hAdvAPI32 == NULL) + return 1; + + pCryptAcquireContext = (CRYPTACQUIRECONTEXTA)GetProcAddress(hAdvAPI32, "CryptAcquireContextA"); + if (!pCryptAcquireContext) + return 1; + + pCryptGenRandom = (CRYPTGENRANDOM)GetProcAddress(hAdvAPI32, "CryptGenRandom"); + if (!pCryptGenRandom) + return 1; + + pCryptReleaseContext = (CRYPTRELEASECONTEXT)GetProcAddress(hAdvAPI32, "CryptReleaseContext"); + if (!pCryptReleaseContext) + return 1; + + if (!pCryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) + return 1; + + ok = CryptGenRandom(hCryptProv, sizeof(uint32_t), data); + pCryptReleaseContext(hCryptProv, 0); + + if (!ok) + return 1; + + *seed = buf_to_uint32((char *)data); + return 0; +} +#endif + +/* gettimeofday() and getpid() */ +static int seed_from_timestamp_and_pid(uint32_t *seed) { +#ifdef HAVE_GETTIMEOFDAY + /* XOR of seconds and microseconds */ + struct timeval tv; + gettimeofday(&tv, NULL); + *seed = (uint32_t)tv.tv_sec ^ (uint32_t)tv.tv_usec; +#else + /* Seconds only */ + *seed = (uint32_t)time(NULL); +#endif + + /* XOR with PID for more randomness */ +#if defined(_WIN32) + *seed ^= (uint32_t)_getpid(); +#elif defined(HAVE_GETPID) + *seed ^= (uint32_t)getpid(); +#endif + + return 0; +} + +static uint32_t generate_seed() { + uint32_t seed; + int done = 0; + +#if !defined(_WIN32) && defined(USE_URANDOM) + if (!done && seed_from_urandom(&seed) == 0) + done = 1; +#endif + +#if defined(_WIN32) && defined(USE_WINDOWS_CRYPTOAPI) + if (!done && seed_from_windows_cryptoapi(&seed) == 0) + done = 1; +#endif + + if (!done) { + /* Fall back to timestamp and PID if no better randomness is + available */ + seed_from_timestamp_and_pid(&seed); + } + + /* Make sure the seed is never zero */ + if (seed == 0) + seed = 1; + + return seed; +} + + +volatile uint32_t hashtable_seed = 0; + +#if defined(HAVE_ATOMIC_BUILTINS) && (defined(HAVE_SCHED_YIELD) || !defined(_WIN32)) +static volatile char seed_initialized = 0; + +void json_object_seed(size_t seed) { + uint32_t new_seed = (uint32_t)seed; + + if (hashtable_seed == 0) { + if (__atomic_test_and_set(&seed_initialized, __ATOMIC_RELAXED) == 0) { + /* Do the seeding ourselves */ + if (new_seed == 0) + new_seed = generate_seed(); + + __atomic_store_n(&hashtable_seed, new_seed, __ATOMIC_ACQ_REL); + } else { + /* Wait for another thread to do the seeding */ + do { +#ifdef HAVE_SCHED_YIELD + sched_yield(); +#endif + } while(__atomic_load_n(&hashtable_seed, __ATOMIC_ACQUIRE) == 0); + } + } +} +#elif defined(HAVE_SYNC_BUILTINS) && (defined(HAVE_SCHED_YIELD) || !defined(_WIN32)) +void json_object_seed(size_t seed) { + uint32_t new_seed = (uint32_t)seed; + + if (hashtable_seed == 0) { + if (new_seed == 0) { + /* Explicit synchronization fences are not supported by the + __sync builtins, so every thread getting here has to + generate the seed value. + */ + new_seed = generate_seed(); + } + + do { + if (__sync_bool_compare_and_swap(&hashtable_seed, 0, new_seed)) { + /* We were the first to seed */ + break; + } else { + /* Wait for another thread to do the seeding */ +#ifdef HAVE_SCHED_YIELD + sched_yield(); +#endif + } + } while(hashtable_seed == 0); + } +} +#elif defined(_WIN32) +static long seed_initialized = 0; +void json_object_seed(size_t seed) { + uint32_t new_seed = (uint32_t)seed; + + if (hashtable_seed == 0) { + if (InterlockedIncrement(&seed_initialized) == 1) { + /* Do the seeding ourselves */ + if (new_seed == 0) + new_seed = generate_seed(); + + hashtable_seed = new_seed; + } else { + /* Wait for another thread to do the seeding */ + do { + SwitchToThread(); + } while (hashtable_seed == 0); + } + } +} +#else +/* Fall back to a thread-unsafe version */ +void json_object_seed(size_t seed) { + uint32_t new_seed = (uint32_t)seed; + + if (hashtable_seed == 0) { + if (new_seed == 0) + new_seed = generate_seed(); + + hashtable_seed = new_seed; + } +} +#endif |