129 lines
4.2 KiB
C
129 lines
4.2 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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#include <sys/param.h>
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#include <sys/errno.h>
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#include <sys/limits.h>
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#include <sys/proc.h>
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#include <sys/random.h>
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#include <sys/sysproto.h>
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#include <sys/systm.h>
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#include <sys/uio.h>
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#define GRND_VALIDFLAGS (GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE)
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/*
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* read_random_uio(9) returns EWOULDBLOCK if a nonblocking request would block,
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* but the Linux API name is EAGAIN. On FreeBSD, they have the same numeric
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* value for now.
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*/
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CTASSERT(EWOULDBLOCK == EAGAIN);
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static int
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kern_getrandom(struct thread *td, void *user_buf, size_t buflen,
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unsigned int flags)
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{
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struct uio auio;
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struct iovec aiov;
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int error;
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if ((flags & ~GRND_VALIDFLAGS) != 0)
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return (EINVAL);
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if (buflen > IOSIZE_MAX)
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return (EINVAL);
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/*
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* Linux compatibility: We have two choices for handling Linux's
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* GRND_INSECURE.
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*
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* 1. We could ignore it completely (like GRND_RANDOM). However, this
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* might produce the surprising result of GRND_INSECURE requests
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* blocking, when the Linux API does not block.
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*
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* 2. Alternatively, we could treat GRND_INSECURE requests as requests
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* for GRND_NONBLOCK. Here, the surprising result for Linux programs
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* is that invocations with unseeded random(4) will produce EAGAIN,
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* rather than garbage.
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*
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* Honoring the flag in the way Linux does seems fraught. If we
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* actually use the output of a random(4) implementation prior to
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* seeding, we leak some entropy about the initial seed to attackers.
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* This seems unacceptable -- it defeats the purpose of blocking on
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* initial seeding.
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*
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* Secondary to that concern, before seeding we may have arbitrarily
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* little entropy collected; producing output from zero or a handful of
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* entropy bits does not seem particularly useful to userspace.
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*
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* If userspace can accept garbage, insecure non-random bytes, they can
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* create their own insecure garbage with srandom(time(NULL)) or
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* similar. Asking the kernel to produce it from the secure
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* getrandom(2) API seems inane.
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*
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* We elect to emulate GRND_INSECURE as an alternative spelling of
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* GRND_NONBLOCK (2).
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*/
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if ((flags & GRND_INSECURE) != 0)
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flags |= GRND_NONBLOCK;
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if (buflen == 0) {
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td->td_retval[0] = 0;
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return (0);
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}
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aiov.iov_base = user_buf;
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aiov.iov_len = buflen;
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auio.uio_iov = &aiov;
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auio.uio_iovcnt = 1;
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auio.uio_offset = 0;
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auio.uio_resid = buflen;
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auio.uio_segflg = UIO_USERSPACE;
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auio.uio_rw = UIO_READ;
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auio.uio_td = td;
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error = read_random_uio(&auio, (flags & GRND_NONBLOCK) != 0);
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if (error == 0)
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td->td_retval[0] = buflen - auio.uio_resid;
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return (error);
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}
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#ifndef _SYS_SYSPROTO_H_
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struct getrandom_args {
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void *buf;
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size_t buflen;
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unsigned int flags;
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};
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#endif
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int
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sys_getrandom(struct thread *td, struct getrandom_args *uap)
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{
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return (kern_getrandom(td, uap->buf, uap->buflen, uap->flags));
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}
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