/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* 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 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/errno.h>
#include <sys/limits.h>
#include <sys/proc.h>
#include <sys/random.h>
#include <sys/sysproto.h>
#include <sys/systm.h>
#include <sys/uio.h>
#define GRND_VALIDFLAGS (GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)
/*
* random_read_uio(9) returns EWOULDBLOCK if a nonblocking request would block,
* but the Linux API name is EAGAIN. On FreeBSD, they have the same numeric
* value for now.
*/
CTASSERT(EWOULDBLOCK == EAGAIN);
static int
kern_getrandom(struct thread *td, void *user_buf, size_t buflen,
unsigned int flags)
{
struct uio auio;
struct iovec aiov;
int error;
if ((flags & ~GRND_VALIDFLAGS) != 0)
return (EINVAL);
if (buflen > IOSIZE_MAX)
return (EINVAL);
/*
* Linux compatibility: We have two choices for handling Linux's
* GRND_INSECURE.
*
* 1. We could ignore it completely (like GRND_RANDOM). However, this
* might produce the surprising result of GRND_INSECURE requests
* blocking, when the Linux API does not block.
*
* 2. Alternatively, we could treat GRND_INSECURE requests as requests
* for GRND_NONBLOCK. Here, the surprising result for Linux programs
* is that invocations with unseeded random(4) will produce EAGAIN,
* rather than garbage.
*
* Honoring the flag in the way Linux does seems fraught. If we
* actually use the output of a random(4) implementation prior to
* seeding, we leak some entropy about the initial seed to attackers.
* This seems unacceptable -- it defeats the purpose of blocking on
* initial seeding.
*
* Secondary to that concern, before seeding we may have arbitrarily
* little entropy collected; producing output from zero or a handful of
* entropy bits does not seem particularly useful to userspace.
*
* If userspace can accept garbage, insecure non-random bytes, they can
* create their own insecure garbage with srandom(time(NULL)) or
* similar. Asking the kernel to produce it from the secure
* getrandom(2) API seems inane.
*
* We elect to emulate GRND_INSECURE as an alternative spelling of
* GRND_NONBLOCK (2).
*/
if ((flags & GRND_INSECURE) != 0)
flags |= GRND_NONBLOCK;
if (buflen == 0) {
td->td_retval[0] = 0;
return (0);
}
aiov.iov_base = user_buf;
aiov.iov_len = buflen;
auio.uio_iov = &aiov;
auio.uio_iovcnt = 1;
auio.uio_offset = 0;
auio.uio_resid = buflen;
auio.uio_segflg = UIO_USERSPACE;
auio.uio_rw = UIO_READ;
auio.uio_td = td;
error = read_random_uio(&auio, (flags & GRND_NONBLOCK) != 0);
if (error == 0)
td->td_retval[0] = buflen - auio.uio_resid;
return (error);
}
#ifndef _SYS_SYSPROTO_H_
struct getrandom_args {
void *buf;
size_t buflen;
unsigned int flags;
};
#endif
int
sys_getrandom(struct thread *td, struct getrandom_args *uap)
{
return (kern_getrandom(td, uap->buf, uap->buflen, uap->flags));
}
