fixes #1083 Random number improvements

1 files changed, 58 insertions, 0 deletions

diff --git a/src/platform/posix/posix_rand_urandom.c b/src/platform/posix/posix_rand_urandom.c
new file mode 100644
index 00000000..32ea6a51
--- /dev/null
+++ b/src/platform/posix/posix_rand_urandom.c
@@ -0,0 +1,58 @@
+//
+// Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
+//
+// This software is supplied under the terms of the MIT License, a
+// copy of which should be located in the distribution where this
+// file was obtained (LICENSE.txt).  A copy of the license may also be
+// found online at https://opensource.org/licenses/MIT.
+//
+
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "core/nng_impl.h"
+
+// The historic /dev/urandom device.  This is not as a good as
+// a system call, since file descriptor attacks are possible,  and it may
+// need special permissions. Modern advice is to always use /dev/urandom
+// unless you have very particular reasons for doing otherwise.
+// If you're in this code base, you're probably on either an ancient OS,
+// or one of the off-beat ones that hasn't updated for support with
+// arc4random or getrandom.
+
+// We could use ISAAC or something like that to seed it only once,
+// but instead we just keep our file descriptor open.  This will have
+// the apparent effect of leaking these file descriptors across fork.
+
+static int             urandom_fd   = -1;
+static pthread_mutex_t urandom_lock = PTHREAD_MUTEX_INITIALIZER;
+
+#ifndef O_CLOEXEC
+#define O_CLOEXEC 0u
+#endif
+
+uint32_t
+nni_random(void)
+{
+	int      fd;
+	uint32_t val;
+
+	(void) pthread_mutex_lock(&urandom_lock);
+	if ((fd = urandom_fd) == -1) {
+		if ((fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC)) < 0) {
+			(void) pthread_mutex_unlock(&urandom_lock);
+			nni_panic("failed to open /dev/urandom");
+		}
+		urandom_fd = fd;
+	}
+	(void) pthread_mutex_unlock(&urandom_lock);
+
+	if (read(fd, &val, sizeof(val)) != sizeof(val)) {
+		nni_panic("failed reading /dev/urandom");
+	}
+	return (val);
+}
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