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0eba6be1b8
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150 lines
3.1 KiB
C
150 lines
3.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_strong_random.c
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* generate a cryptographically secure random number
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*
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* Our definition of "strong" is that it's suitable for generating random
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* salts and query cancellation keys, during authentication.
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*
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* Copyright (c) 1996-2017, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* src/port/pg_strong_random.c
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef FRONTEND
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#include "postgres.h"
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#else
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#include "postgres_fe.h"
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#endif
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/time.h>
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#ifdef USE_OPENSSL
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#include <openssl/rand.h>
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#endif
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#ifdef WIN32
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#include <wincrypt.h>
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#endif
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#ifdef WIN32
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/*
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* Cache a global crypto provider that only gets freed when the process
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* exits, in case we need random numbers more than once.
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*/
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static HCRYPTPROV hProvider = 0;
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#endif
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#if defined(USE_DEV_URANDOM)
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/*
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* Read (random) bytes from a file.
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*/
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static bool
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random_from_file(char *filename, void *buf, size_t len)
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{
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int f;
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char *p = buf;
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ssize_t res;
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f = open(filename, O_RDONLY, 0);
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if (f == -1)
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return false;
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while (len)
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{
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res = read(f, p, len);
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if (res <= 0)
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{
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if (errno == EINTR)
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continue; /* interrupted by signal, just retry */
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close(f);
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return false;
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}
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p += res;
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len -= res;
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}
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close(f);
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return true;
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}
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#endif
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/*
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* pg_strong_random
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*
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* Generate requested number of random bytes. The returned bytes are
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* cryptographically secure, suitable for use e.g. in authentication.
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*
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* We rely on system facilities for actually generating the numbers.
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* We support a number of sources:
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*
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* 1. OpenSSL's RAND_bytes()
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* 2. Windows' CryptGenRandom() function
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* 3. /dev/urandom
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*
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* The configure script will choose which one to use, and set
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* a USE_*_RANDOM flag accordingly.
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*
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* Returns true on success, and false if none of the sources
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* were available. NB: It is important to check the return value!
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* Proceeding with key generation when no random data was available
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* would lead to predictable keys and security issues.
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*/
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bool
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pg_strong_random(void *buf, size_t len)
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{
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/*
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* When built with OpenSSL, use OpenSSL's RAND_bytes function.
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*/
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#if defined(USE_OPENSSL_RANDOM)
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if (RAND_bytes(buf, len) == 1)
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return true;
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return false;
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/*
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* Windows has CryptoAPI for strong cryptographic numbers.
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*/
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#elif defined(USE_WIN32_RANDOM)
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if (hProvider == 0)
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{
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if (!CryptAcquireContext(&hProvider,
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NULL,
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MS_DEF_PROV,
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PROV_RSA_FULL,
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CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
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{
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/*
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* On failure, set back to 0 in case the value was for some reason
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* modified.
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*/
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hProvider = 0;
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}
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}
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/* Re-check in case we just retrieved the provider */
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if (hProvider != 0)
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{
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if (CryptGenRandom(hProvider, len, buf))
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return true;
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}
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return false;
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/*
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* Read /dev/urandom ourselves.
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*/
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#elif defined(USE_DEV_URANDOM)
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if (random_from_file("/dev/urandom", buf, len))
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return true;
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return false;
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#else
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/* The autoconf script should not have allowed this */
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#error no source of random numbers configured
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#endif
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}
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