1 files changed, 158 insertions, 0 deletions
diff --git a/src/backend/utils/misc/backend_random.c b/src/backend/utils/misc/backend_random.c
new file mode 100644
index 00000000000..1bc239d1ddc
--- /dev/null
+++ b/src/backend/utils/misc/backend_random.c
@@ -0,0 +1,158 @@
+/*-------------------------------------------------------------------------
+ *
+ * backend_random.c
+ *	  Backend random number generation routine.
+ *
+ * pg_backend_random() function fills a buffer with random bytes. Normally,
+ * it is just a thin wrapper around pg_strong_random(), but when compiled
+ * with --disable-strong-random, we provide a built-in implementation.
+ *
+ * This function is used for generating nonces in authentication, and for
+ * random salt generation in pgcrypto. The built-in implementation is not
+ * cryptographically strong, but if the user asked for it, we'll go ahead
+ * and use it anyway.
+ *
+ * The built-in implementation uses the standard erand48 algorithm, with
+ * a seed shared between all backends.
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/misc/backend_random.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <sys/time.h>
+
+#include "miscadmin.h"
+#include "storage/lwlock.h"
+#include "storage/shmem.h"
+#include "utils/backend_random.h"
+#include "utils/timestamp.h"
+
+#ifdef HAVE_STRONG_RANDOM
+
+Size
+BackendRandomShmemSize(void)
+{
+	return 0;
+}
+
+void
+BackendRandomShmemInit(void)
+{
+	/* do nothing */
+}
+
+bool
+pg_backend_random(char *dst, int len)
+{
+	/* should not be called in postmaster */
+	Assert (IsUnderPostmaster || !IsPostmasterEnvironment);
+
+	return pg_strong_random(dst, len);
+}
+
+#else
+
+/*
+ * Seed for the PRNG, stored in shared memory.
+ *
+ * Protected by BackendRandomLock.
+ */
+typedef struct
+{
+	bool		initialized;
+	unsigned short seed[3];
+} BackendRandomShmemStruct;
+
+static BackendRandomShmemStruct *BackendRandomShmem;
+
+Size
+BackendRandomShmemSize(void)
+{
+	return sizeof(BackendRandomShmemStruct);
+}
+
+void
+BackendRandomShmemInit(void)
+{
+	bool		found;
+
+	BackendRandomShmem = (BackendRandomShmemStruct *)
+		ShmemInitStruct("Backend PRNG state",
+						BackendRandomShmemSize(),
+						&found);
+
+	if (!IsUnderPostmaster)
+	{
+		Assert(!found);
+
+		BackendRandomShmem->initialized = false;
+	}
+	else
+		Assert(found);
+}
+
+bool
+pg_backend_random(char *dst, int len)
+{
+	int			i;
+	char	   *end = dst + len;
+
+	/* should not be called in postmaster */
+	Assert (IsUnderPostmaster || !IsPostmasterEnvironment);
+
+	LWLockAcquire(BackendRandomLock, LW_EXCLUSIVE);
+
+	/*
+	 * Seed the PRNG on the first use.
+	 */
+	if (!BackendRandomShmem->initialized)
+	{
+		struct timeval now;
+
+		gettimeofday(&now, NULL);
+
+		BackendRandomShmem->seed[0] = now.tv_sec;
+		BackendRandomShmem->seed[1] = (unsigned short) (now.tv_usec);
+		BackendRandomShmem->seed[2] = (unsigned short) (now.tv_usec >> 16);
+
+		/*
+		 * Mix in the cancel key, generated by the postmaster. This adds
+		 * what little entropy the postmaster had to the seed.
+		 */
+		BackendRandomShmem->seed[0] ^= (MyCancelKey);
+		BackendRandomShmem->seed[1] ^= (MyCancelKey >> 16);
+
+		BackendRandomShmem->initialized = true;
+	}
+
+	for (i = 0; dst < end; i++)
+	{
+		uint32		r;
+		int			j;
+
+		/*
+		 * pg_jrand48 returns a 32-bit integer. Fill the next 4 bytes from it.
+		 */
+		r  = (uint32) pg_jrand48(BackendRandomShmem->seed);
+
+		for (j = 0; j < 4 && dst < end; j++)
+		{
+			*(dst++) = (char) (r & 0xFF);
+			r >>= 8;
+		}
+	}
+	LWLockRelease(BackendRandomLock);
+
+	return true;
+}
+
+
+#endif /* HAVE_STRONG_RANDOM */