246 lines
7.0 KiB
C
246 lines
7.0 KiB
C
/* $NetBSD: sys_getrandom.c,v 1.2 2021/12/28 13:22:43 riastradh Exp $ */
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/*-
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* Copyright (c) 2020 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Taylor R. Campbell.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* getrandom() system call
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: sys_getrandom.c,v 1.2 2021/12/28 13:22:43 riastradh Exp $");
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/atomic.h>
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#include <sys/cprng.h>
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#include <sys/entropy.h>
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#include <sys/kmem.h>
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#include <sys/lwp.h>
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#include <sys/proc.h>
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#include <sys/random.h>
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#include <sys/sched.h>
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#include <sys/signalvar.h>
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#include <sys/syscallargs.h>
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#include <sys/uio.h>
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#include <crypto/nist_hash_drbg/nist_hash_drbg.h>
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#define RANDOM_BUFSIZE 512
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int
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dogetrandom(struct uio *uio, unsigned int flags)
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{
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uint8_t seed[NIST_HASH_DRBG_SEEDLEN_BYTES] = {0};
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struct nist_hash_drbg drbg;
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uint8_t *buf;
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int extractflags = 0;
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int error;
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KASSERT((flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) == 0);
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KASSERT((flags & (GRND_RANDOM|GRND_INSECURE)) !=
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(GRND_RANDOM|GRND_INSECURE));
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/* Get a buffer for transfers. */
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buf = kmem_alloc(RANDOM_BUFSIZE, KM_SLEEP);
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/*
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* Fast path: for short reads other than from /dev/random, if
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* seeded or if INSECURE, just draw from per-CPU cprng_strong.
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*/
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if (uio->uio_resid <= RANDOM_BUFSIZE &&
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!ISSET(flags, GRND_RANDOM) &&
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(entropy_ready() || ISSET(flags, GRND_INSECURE))) {
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/* Generate data and transfer it out. */
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cprng_strong(user_cprng, buf, uio->uio_resid, 0);
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error = uiomove(buf, uio->uio_resid, uio);
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goto out;
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}
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/*
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* Try to get a seed from the entropy pool. Fail if we would
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* block. If GRND_INSECURE, always return something even if it
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* is partial entropy; if !GRND_INSECURE, set ENTROPY_HARDFAIL
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* in order to tell entropy_extract not to bother drawing
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* anything from a partial pool if we can't get full entropy.
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*/
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if (!ISSET(flags, GRND_NONBLOCK) && !ISSET(flags, GRND_INSECURE))
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extractflags |= ENTROPY_WAIT|ENTROPY_SIG;
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if (!ISSET(flags, GRND_INSECURE))
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extractflags |= ENTROPY_HARDFAIL;
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error = entropy_extract(seed, sizeof seed, extractflags);
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if (error && !ISSET(flags, GRND_INSECURE))
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goto out;
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/* Instantiate the DRBG. */
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if (nist_hash_drbg_instantiate(&drbg, seed, sizeof seed, NULL, 0,
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NULL, 0))
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panic("nist_hash_drbg_instantiate");
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/* Promptly zero the seed. */
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explicit_memset(seed, 0, sizeof seed);
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/* Generate data. */
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error = 0;
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while (uio->uio_resid) {
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size_t n = MIN(uio->uio_resid, RANDOM_BUFSIZE);
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/*
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* Clamp /dev/random output to the entropy capacity and
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* seed size. Programs can't rely on long reads.
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*/
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if (ISSET(flags, GRND_RANDOM)) {
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n = MIN(n, ENTROPY_CAPACITY);
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n = MIN(n, sizeof seed);
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/*
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* Guarantee never to return more than one
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* buffer in this case to minimize bookkeeping.
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*/
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CTASSERT(ENTROPY_CAPACITY <= RANDOM_BUFSIZE);
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CTASSERT(sizeof seed <= RANDOM_BUFSIZE);
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}
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/*
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* Try to generate a block of data, but if we've hit
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* the DRBG reseed interval, reseed.
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*/
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if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0)) {
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/*
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* Get a fresh seed without blocking -- we have
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* already generated some output so it is not
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* useful to block. This can fail only if the
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* request is obscenely large, so it is OK for
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* either /dev/random or /dev/urandom to fail:
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* we make no promises about gigabyte-sized
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* reads happening all at once.
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*/
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error = entropy_extract(seed, sizeof seed,
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ENTROPY_HARDFAIL);
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if (error)
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break;
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/* Reseed and try again. */
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if (nist_hash_drbg_reseed(&drbg, seed, sizeof seed,
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NULL, 0))
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panic("nist_hash_drbg_reseed");
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/* Promptly zero the seed. */
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explicit_memset(seed, 0, sizeof seed);
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/* If it fails now, that's a bug. */
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if (nist_hash_drbg_generate(&drbg, buf, n, NULL, 0))
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panic("nist_hash_drbg_generate");
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}
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/* Transfer n bytes out. */
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error = uiomove(buf, n, uio);
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if (error)
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break;
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/*
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* If this is /dev/random, stop here, return what we
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* have, and force the next read to reseed. Programs
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* can't rely on /dev/random for long reads.
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*/
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if (ISSET(flags, GRND_RANDOM)) {
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error = 0;
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break;
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}
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/* Now's a good time to yield if needed. */
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preempt_point();
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/* Check for interruption after at least 256 bytes. */
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CTASSERT(RANDOM_BUFSIZE >= 256);
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if (__predict_false(curlwp->l_flag & LW_PENDSIG) &&
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sigispending(curlwp, 0)) {
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error = EINTR;
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break;
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}
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}
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out: /* Zero the buffer and free it. */
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explicit_memset(buf, 0, RANDOM_BUFSIZE);
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kmem_free(buf, RANDOM_BUFSIZE);
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return error;
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}
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int
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sys_getrandom(struct lwp *l, const struct sys_getrandom_args *uap,
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register_t *retval)
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{
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/* {
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syscallarg(void *) buf;
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syscallarg(size_t) buflen;
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syscallarg(unsigned) flags;
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} */
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void *buf = SCARG(uap, buf);
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size_t buflen = SCARG(uap, buflen);
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int flags = SCARG(uap, flags);
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int error;
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/* Set up an iov and uio to read into the user's buffer. */
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struct iovec iov = { .iov_base = buf, .iov_len = buflen };
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struct uio uio = {
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.uio_iov = &iov,
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.uio_iovcnt = 1,
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.uio_offset = 0,
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.uio_resid = buflen,
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.uio_rw = UIO_READ,
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.uio_vmspace = curproc->p_vmspace,
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};
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/* Validate the flags. */
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if (flags & ~(GRND_RANDOM|GRND_INSECURE|GRND_NONBLOCK)) {
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/* Unknown flags. */
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error = EINVAL;
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goto out;
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}
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if ((flags & (GRND_RANDOM|GRND_INSECURE)) ==
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(GRND_RANDOM|GRND_INSECURE)) {
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/* Nonsensical combination. */
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error = EINVAL;
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goto out;
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}
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/* Do it. */
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error = dogetrandom(&uio, flags);
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out: /*
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* If we transferred anything, return the number of bytes
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* transferred and suppress error; otherwise return the error.
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*/
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*retval = buflen - uio.uio_resid;
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if (*retval)
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error = 0;
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return error;
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}
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