freebsd-nq/lib/libc/sys/getrandom.2

.\" Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
.\" 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.
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.\" 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
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" $FreeBSD$
.\"
.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 .
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 2018-03-21 01:15:45 +00:00			`.\" Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>`
			`.\" 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 .`