1 files changed, 149 insertions, 0 deletions
diff --git a/src/port/pg_strong_random.c b/src/port/pg_strong_random.c
new file mode 100644
index 00000000000..6d3aa38efdd
--- /dev/null
+++ b/src/port/pg_strong_random.c
@@ -0,0 +1,149 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_strong_random.c
+ *	  generate a cryptographically secure random number
+ *
+ * Our definition of "strong" is that it's suitable for generating random
+ * salts and query cancellation keys, during authentication.
+ *
+ * Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/port/pg_strong_random.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/time.h>
+
+#ifdef USE_OPENSSL
+#include <openssl/rand.h>
+#endif
+#ifdef WIN32
+#include <Wincrypt.h>
+#endif
+
+#ifdef WIN32
+/*
+ * Cache a global crypto provider that only gets freed when the process
+ * exits, in case we need random numbers more than once.
+ */
+static HCRYPTPROV hProvider = 0;
+#endif
+
+#if defined(USE_DEV_URANDOM)
+/*
+ * Read (random) bytes from a file.
+ */
+static bool
+random_from_file(char *filename, void *buf, size_t len)
+{
+	int			f;
+	char	   *p = buf;
+	ssize_t		res;
+
+	f = open(filename, O_RDONLY, 0);
+	if (f == -1)
+		return false;
+
+	while (len)
+	{
+		res = read(f, p, len);
+		if (res <= 0)
+		{
+			if (errno == EINTR)
+				continue;		/* interrupted by signal, just retry */
+
+			close(f);
+			return false;
+		}
+
+		p += res;
+		len -= res;
+	}
+
+	close(f);
+	return true;
+}
+#endif
+
+/*
+ * pg_strong_random
+ *
+ * Generate requested number of random bytes. The returned bytes are
+ * cryptographically secure, suitable for use e.g. in authentication.
+ *
+ * We rely on system facilities for actually generating the numbers.
+ * We support a number of sources:
+ *
+ * 1. OpenSSL's RAND_bytes()
+ * 2. Windows' CryptGenRandom() function
+ * 3. /dev/urandom
+ *
+ * The configure script will choose which one to use, and set
+ * a USE_*_RANDOM flag accordingly.
+ *
+ * Returns true on success, and false if none of the sources
+ * were available. NB: It is important to check the return value!
+ * Proceeding with key generation when no random data was available
+ * would lead to predictable keys and security issues.
+ */
+bool
+pg_strong_random(void *buf, size_t len)
+{
+	/*
+	 * When built with OpenSSL, use OpenSSL's RAND_bytes function.
+	 */
+#if defined(USE_OPENSSL_RANDOM)
+	if (RAND_bytes(buf, len) == 1)
+		return true;
+	return false;
+
+	/*
+	 * Windows has CryptoAPI for strong cryptographic numbers.
+	 */
+#elif defined(USE_WIN32_RANDOM)
+	if (hProvider == 0)
+	{
+		if (!CryptAcquireContext(&hProvider,
+								 NULL,
+								 MS_DEF_PROV,
+								 PROV_RSA_FULL,
+								 CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
+		{
+			/*
+			 * On failure, set back to 0 in case the value was for some reason
+			 * modified.
+			 */
+			hProvider = 0;
+		}
+	}
+	/* Re-check in case we just retrieved the provider */
+	if (hProvider != 0)
+	{
+		if (CryptGenRandom(hProvider, len, buf))
+			return true;
+	}
+	return false;
+
+	/*
+	 * Read /dev/urandom ourselves.
+	 */
+#elif defined(USE_DEV_URANDOM)
+	if (random_from_file("/dev/urandom", buf, len))
+		return true;
+	return false;
+
+#else
+	/* The autoconf script should not have allowed this */
+#error no source of random numbers configured
+#endif
+}