Implement getrandom(2) and getentropy(3)

The general idea here is to provide userspace programs with well-defined
sources of entropy, in a fashion that doesn't require opening a new file
descriptor (ulimits) or accessing paths (/dev/urandom may be restricted
by chroot or capsicum).

getrandom(2) is the more general API, and comes from the Linux world.
Since our urandom and random devices are identical, the GRND_RANDOM flag
is ignored.

getentropy(3) is added as a compatibility shim for the OpenBSD API.

truss(1) support is included.

Tests for both system calls are provided.  Coverage is believed to be at
least as comprehensive as LTP getrandom(2) test coverage.  Additionally,
instructions for running the LTP tests directly against FreeBSD are provided
in the "Test Plan" section of the Differential revision linked below.  (They
pass, of course.)

PR:		194204
Reported by:	David CARLIER <david.carlier AT hardenedbsd.org>
Discussed with:	cperciva, delphij, jhb, markj
Relnotes:	maybe
Differential Revision:	https://reviews.freebsd.org/D14500

include/unistd.h

@@ -506,6 +506,7 @@ int	 execvP(const char *, const char *, char * const *);
 int	 feature_present(const char *);
 char	*fflagstostr(u_long);
 int	 getdomainname(char *, int);
+int	 getentropy(void *, size_t);
 int	 getgrouplist(const char *, gid_t, gid_t *, int *);
 int	 getloginclass(char *, size_t);
 mode_t	 getmode(const void *, mode_t);

lib/libc/gen/Makefile.inc

@@ -57,6 +57,7 @@ SRCS+=	__getosreldate.c \
 	getcap.c \
 	getcwd.c \
 	getdomainname.c \
+	getentropy.c \
 	getgrent.c \
 	getgrouplist.c \
 	gethostname.c \
@@ -220,6 +221,7 @@ MAN+=	alarm.3 \
 	getcwd.3 \
 	getdiskbyname.3 \
 	getdomainname.3 \
+	getentropy.3 \
 	getfsent.3 \
 	getgrent.3 \
 	getgrouplist.3 \

lib/libc/gen/Symbol.map

@@ -408,6 +408,7 @@ FBSD_1.5 {
 	fts_set;
 	fts_set_clientptr;
 	ftw;
+	getentropy;
 	getmntinfo;
 	glob;
 	globfree;

lib/libc/gen/getentropy.3

@@ -0,0 +1,86 @@
+.\"	$OpenBSD: getentropy.2,v 1.8 2015/01/31 00:20:12 schwarze Exp $
+.\"
+.\" Copyright (c) 2018 Conrad Meyer <[email protected]>
+.\" Copyright (c) 2014 Theo de Raadt
+.\"
+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd February 24, 2018
+.Dt GETENTROPY 3
+.Os
+.Sh NAME
+.Nm getentropy
+.Nd get entropy
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft int
+.Fn getentropy "void *buf" "size_t buflen"
+.Sh DESCRIPTION
+.Fn getentropy
+fills a buffer with high-quality random data.
+.Pp
+The maximum
+.Fa buflen
+permitted is 256 bytes.
+.Pp
+If it does not produce an error,
+.Fn getentropy
+always provides the requested number of bytes of random data.
+.Pp
+Similar to reading from
+.Pa /dev/urandom
+just after boot,
+.Fn getentropy
+may block until the system has collected enough entropy to seed the CSPRNG.
+.Sh IMPLEMENTATION NOTES
+The
+.Fn getentropy
+function is implemented using
+.Xr getrandom 2 .
+.Sh RETURN VALUES
+.Rv -std
+.Sh ERRORS
+.Fn getentropy
+will succeed unless:
+.Bl -tag -width Er
+.It Bq Er EFAULT
+The
+.Fa buf
+parameter points to an
+invalid address.
+.It Bq Er EIO
+Too many bytes requested, or some other fatal error occurred.
+.El
+.Sh SEE ALSO
+.Xr arc4random 3 ,
+.Xr getrandom 2 ,
+.Xr random 4
+.Sh STANDARDS
+.Fn getentropy
+is non-standard.
+It is present on
+.Ox
+and Linux.
+.Sh HISTORY
+The
+.Fn getentropy
+function appeared in
+.Ox 5.6 .
+The
+.Fx
+libc compatibility shim first appeared in
+.Fx 12.0 .

lib/libc/gen/getentropy.c

@@ -0,0 +1,70 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2018 Conrad Meyer <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/random.h>
+
+#include <errno.h>
+#include <stdlib.h>
+
+#include "libc_private.h"
+
+int
+getentropy(void *buf, size_t buflen)
+{
+	ssize_t rd;
+
+	if (buflen > 256) {
+		errno = EIO;
+		return (-1);
+	}
+
+	while (buflen > 0) {
+		rd = getrandom(buf, buflen, 0);
+		if (rd == -1) {
+			if (errno == EINTR)
+				continue;
+			else if (errno == ENOSYS)
+				abort();
+			else
+				return (-1);
+		}
+
+		/* This cannot happen. */
+		if (rd == 0)
+			abort();
+
+		buf = (char *)buf + rd;
+		buflen -= rd;
+	}
+
+	return (0);
+}

lib/libc/sys/Makefile.inc

@@ -197,6 +197,7 @@ MAN+=	abort2.2 \
 	getpgrp.2 \
 	getpid.2 \
 	getpriority.2 \
+	getrandom.2 \
 	getrlimit.2 \
 	getrusage.2 \
 	getsid.2 \

lib/libc/sys/Symbol.map

@@ -392,6 +392,7 @@ FBSD_1.5 {
 	getdents;
 	getdirentries;
 	getfsstat;
+	getrandom;
 	kevent;
 	lstat;
 	mknod;
@@ -627,6 +628,8 @@ FBSDprivate_1.0 {
 	__sys_getppid;
 	_getpriority;
 	__sys_getpriority;
+	_getrandom;
+	__sys_getrandom;
 	_getresgid;
 	__sys_getresgid;
 	_getresuid;

lib/libc/sys/getrandom.2

@@ -0,0 +1,121 @@
+.\" Copyright (c) 2018 Conrad Meyer <[email protected]>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd February 24, 2018
+.Dt GETRANDOM 2
+.Os
+.Sh NAME
+.Nm getrandom
+.Nd get random data
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In sys/random.h
+.Ft ssize_t
+.Fn getrandom "void *buf" "size_t buflen" "unsigned int flags"
+.Sh DESCRIPTION
+.Fn getrandom
+fills
+.Fa buf
+with up to
+.Fa buflen
+bytes of random data.
+.Pp
+The
+.Fa flags
+argument may include zero or more of the following:
+.Bl -tag -width _GRND_NONBLOCK_
+.It Ql GRND_NONBLOCK
+Return
+.Er EAGAIN
+instead of blocking, if the
+.Xr random 4
+device has not yet been seeded.
+By default,
+.Fn getrandom
+will block until the device is seeded.
+.It Ql GRND_RANDOM
+This flag does nothing on
+.Fx .
+.Pa /dev/random
+and
+.Pa /dev/urandom
+are identical.
+.El
+.Pp
+If the
+.Xr random 4
+device has been seeded, reads of up to 256 bytes will always return as many
+bytes as requested and will not be interrupted by signals.
+.Pp
+.Sh RETURN VALUES
+Upon successful completion, the number of bytes which were actually read is
+returned.
+For requests larger than 256 bytes, this can be fewer bytes than were
+requested.
+Otherwise, -1 is returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+The
+.Fn getrandom
+operation returns the following errors:
+.Bl -tag -width Er
+.It Bq Er EAGAIN
+The
+.Ql GRND_NONBLOCK
+flag was set and the
+.Xr random 4
+device was not yet seeded.
+.It Bq Er EFAULT
+The
+.Fa buf
+parameter points to an invalid address.
+.It Bq Er EINTR
+The sleep was interrupted by a signal.
+.It Bq Er EINVAL
+An invalid
+.Fa flags
+was specified.
+.It Bq Er EINVAL
+The requested
+.Fa buflen
+was larger than
+.Dv IOSIZE_MAX .
+.El
+.Sh SEE ALSO
+.Xr arc4random 3 ,
+.Xr getentropy 3 ,
+.Xr random 4
+.Sh STANDARDS
+.Fn getentropy
+is non-standard.
+It is present in Linux.
+.Sh HISTORY
+The
+.Fn getrandom
+system call first appeared in
+.Fx 12.0 .

lib/libc/tests/gen/Makefile

@@ -10,6 +10,7 @@ ATF_TESTS_C+=		fmtmsg_test
 ATF_TESTS_C+=		fnmatch2_test
 ATF_TESTS_C+=		fpclassify2_test
 ATF_TESTS_C+=		ftw_test
+ATF_TESTS_C+=		getentropy_test
 ATF_TESTS_C+=		getmntinfo_test
 ATF_TESTS_C+=		glob2_test
 ATF_TESTS_C+=		makecontext_test
@@ -61,6 +62,8 @@ NETBSD_ATF_TESTS_C+=	vis_test
 
 .include "../Makefile.netbsd-tests"
 
+CFLAGS.getentropy_test+=	-I${SRCTOP}/include
+LIBADD.getentropy_test+=	c
 LIBADD.humanize_number_test+=	util
 
 LIBADD.fpclassify_test+=m