1 files changed, 92 insertions, 0 deletions
diff --git a/random.c b/random.c
new file mode 100644
index 0000000..eedb52f
--- /dev/null
+++ b/random.c
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "dbg.h"
+
+#ifdef __linux__
+#include <sys/syscall.h>
+#endif
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+#ifndef MAC_OS_X_VERSION_10_12
+#define MAC_OS_X_VERSION_10_12 101200
+#endif
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_12
+#include <sys/random.h>
+#endif
+#endif
+
+static inline bool __attribute__((__warn_unused_result__))
+get_random_bytes(uint8_t *out, size_t len)
+{
+	ssize_t ret = 0;
+	size_t i;
+	int fd;
+
+	if (len > 256) {
+		errno = EOVERFLOW;
+		return false;
+	}
+
+#if defined(__OpenBSD__) ||                                                    \
+	(defined(__APPLE__) &&                                                 \
+	 MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_12) ||           \
+	(defined(__GLIBC__) &&                                                 \
+	 (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25)))
+	if (!getentropy(out, len))
+		return true;
+#endif
+
+#if defined(__NR_getrandom) && defined(__linux__)
+	if (syscall(__NR_getrandom, out, len, 0) == (ssize_t)len)
+		return true;
+#endif
+
+	fd = open("/dev/urandom", O_RDONLY);
+	if (fd < 0)
+		return false;
+	for (errno = 0, i = 0; i < len; i += ret, ret = 0) {
+		ret = read(fd, out + i, len - i);
+		if (ret <= 0) {
+			ret = errno ? -errno : -EIO;
+			break;
+		}
+	}
+	close(fd);
+	errno = -ret;
+	return i == len;
+}
+
+uint64_t random_bounded(uint64_t bound)
+{
+	uint64_t ret;
+
+	if (bound == 0)
+		return 0;
+
+	if (bound == 1) {
+		if (!get_random_bytes((uint8_t *)&ret, sizeof(ret)))
+			fatal("get_random_bytes()");
+		return (ret > 0x7FFFFFFFFFFFFFFF) ? 1 : 0;
+	}
+
+	const uint64_t max_mod_bound = (1 + ~bound) % bound;
+
+	do {
+		if (!get_random_bytes((uint8_t *)&ret, sizeof(ret)))
+			fatal("get_random_bytes()");
+	} while (ret < max_mod_bound);
+
+	return ret % bound;
+}