Add arc4random() etc. from OpenBSD 5.8

According to the OpenBSD man page, "A Replacement Call for Random".  It
offers high quality random numbers derived from input data obtained by
the OpenBSD specific getentropy() system call which is declared in
<unistd.h> and must be implemented for each Newlib port externally.  The
arc4random() functions are used for example in LibreSSL and OpenSSH.

Cygwin provides currently its own implementation of the arc4random
family.  Maybe it makes sense to use this getentropy() implementation:

http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/lib/libcrypto/crypto/getentropy_win.c?rev=1.4&content-type=text/x-cvsweb-markup

	* libc/include/stdlib.h (arc4random): Declare if __BSD_VISIBLE.
	(arc4random_buf): Likewise.
	(arc4random_uniform): Likewise.
	* libc/include/sys/unistd.h (getentropy): Likewise.
	* libc/include/machine/_arc4random.h: New file.
	* libc/stdlib/arc4random.c: Likewise.
	* libc/stdlib/arc4random.h: Likewise.
	* libc/stdlib/arc4random_uniform.c: Likewise.
	* libc/stdlib/chacha_private.h: Likewise.
	* libc/sys/rtems/include/machine/_arc4random.h: Likewise.
	* libc/stdlib/Makefile.am (EXTENDED_SOURCES): Add arc4random.c
	and arc4random_uniform.c.
	* libc/stdlib/Makefile.in: Regenerate.

1 files changed, 195 insertions, 0 deletions

diff --git a/newlib/libc/stdlib/arc4random.c b/newlib/libc/stdlib/arc4random.c
new file mode 100644
index 0000000..75cdff3
--- /dev/null
+++ b/newlib/libc/stdlib/arc4random.c
@@ -0,0 +1,195 @@
+/*	$OpenBSD: arc4random.c,v 1.52 2015/01/16 16:48:51 deraadt Exp $	*/
+
+/*
+ * Copyright (c) 1996, David Mazieres <dm@uun.org>
+ * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
+ * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
+ * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * ChaCha based random number generator for OpenBSD.
+ */
+
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/time.h>
+
+#define KEYSTREAM_ONLY
+#include "chacha_private.h"
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+#ifdef __GNUC__
+#define inline __inline
+#else				/* !__GNUC__ */
+#define inline
+#endif				/* !__GNUC__ */
+
+#define KEYSZ	32
+#define IVSZ	8
+#define BLOCKSZ	64
+#define RSBUFSZ	(16*BLOCKSZ)
+
+/* Marked MAP_INHERIT_ZERO, so zero'd out in fork children. */
+static struct _rs {
+	size_t		rs_have;	/* valid bytes at end of rs_buf */
+	size_t		rs_count;	/* bytes till reseed */
+} *rs;
+
+/* Maybe be preserved in fork children, if _rs_allocate() decides. */
+static struct _rsx {
+	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
+	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
+} *rsx;
+
+static inline int _rs_allocate(struct _rs **, struct _rsx **);
+static inline void _rs_forkdetect(void);
+#include "arc4random.h"
+
+static inline void _rs_rekey(u_char *dat, size_t datlen);
+
+static inline void
+_rs_init(u_char *buf, size_t n)
+{
+	if (n < KEYSZ + IVSZ)
+		return;
+
+	if (rs == NULL) {
+		if (_rs_allocate(&rs, &rsx) == -1)
+			abort();
+	}
+
+	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);
+	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ);
+}
+
+static void
+_rs_stir(void)
+{
+	u_char rnd[KEYSZ + IVSZ];
+
+	if (getentropy(rnd, sizeof rnd) == -1)
+		_getentropy_fail();
+
+	if (!rs)
+		_rs_init(rnd, sizeof(rnd));
+	else
+		_rs_rekey(rnd, sizeof(rnd));
+	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
+
+	/* invalidate rs_buf */
+	rs->rs_have = 0;
+	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
+
+	rs->rs_count = 1600000;
+}
+
+static inline void
+_rs_stir_if_needed(size_t len)
+{
+	_rs_forkdetect();
+	if (!rs || rs->rs_count <= len)
+		_rs_stir();
+	if (rs->rs_count <= len)
+		rs->rs_count = 0;
+	else
+		rs->rs_count -= len;
+}
+
+static inline void
+_rs_rekey(u_char *dat, size_t datlen)
+{
+#ifndef KEYSTREAM_ONLY
+	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
+#endif
+	/* fill rs_buf with the keystream */
+	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
+	    rsx->rs_buf, sizeof(rsx->rs_buf));
+	/* mix in optional user provided data */
+	if (dat) {
+		size_t i, m;
+
+		m = min(datlen, KEYSZ + IVSZ);
+		for (i = 0; i < m; i++)
+			rsx->rs_buf[i] ^= dat[i];
+	}
+	/* immediately reinit for backtracking resistance */
+	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
+	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
+	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
+}
+
+static inline void
+_rs_random_buf(void *_buf, size_t n)
+{
+	u_char *buf = (u_char *)_buf;
+	u_char *keystream;
+	size_t m;
+
+	_rs_stir_if_needed(n);
+	while (n > 0) {
+		if (rs->rs_have > 0) {
+			m = min(n, rs->rs_have);
+			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
+			    - rs->rs_have;
+			memcpy(buf, keystream, m);
+			memset(keystream, 0, m);
+			buf += m;
+			n -= m;
+			rs->rs_have -= m;
+		}
+		if (rs->rs_have == 0)
+			_rs_rekey(NULL, 0);
+	}
+}
+
+static inline void
+_rs_random_u32(uint32_t *val)
+{
+	u_char *keystream;
+
+	_rs_stir_if_needed(sizeof(*val));
+	if (rs->rs_have < sizeof(*val))
+		_rs_rekey(NULL, 0);
+	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
+	memcpy(val, keystream, sizeof(*val));
+	memset(keystream, 0, sizeof(*val));
+	rs->rs_have -= sizeof(*val);
+}
+
+uint32_t
+arc4random(void)
+{
+	uint32_t val;
+
+	_ARC4_LOCK();
+	_rs_random_u32(&val);
+	_ARC4_UNLOCK();
+	return val;
+}
+
+void
+arc4random_buf(void *buf, size_t n)
+{
+	_ARC4_LOCK();
+	_rs_random_buf(buf, n);
+	_ARC4_UNLOCK();
+}