1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/errno.h> 34 #include <sys/limits.h> 35 #include <sys/proc.h> 36 #include <sys/random.h> 37 #include <sys/sysproto.h> 38 #include <sys/systm.h> 39 #include <sys/uio.h> 40 41 #define GRND_VALIDFLAGS (GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE) 42 43 /* 44 * random_read_uio(9) returns EWOULDBLOCK if a nonblocking request would block, 45 * but the Linux API name is EAGAIN. On FreeBSD, they have the same numeric 46 * value for now. 47 */ 48 CTASSERT(EWOULDBLOCK == EAGAIN); 49 50 static int 51 kern_getrandom(struct thread *td, void *user_buf, size_t buflen, 52 unsigned int flags) 53 { 54 struct uio auio; 55 struct iovec aiov; 56 int error; 57 58 if ((flags & ~GRND_VALIDFLAGS) != 0) 59 return (EINVAL); 60 if (buflen > IOSIZE_MAX) 61 return (EINVAL); 62 63 /* 64 * Linux compatibility: We have two choices for handling Linux's 65 * GRND_INSECURE. 66 * 67 * 1. We could ignore it completely (like GRND_RANDOM). However, this 68 * might produce the surprising result of GRND_INSECURE requests 69 * blocking, when the Linux API does not block. 70 * 71 * 2. Alternatively, we could treat GRND_INSECURE requests as requests 72 * for GRND_NONBLOCK. Here, the surprising result for Linux programs 73 * is that invocations with unseeded random(4) will produce EAGAIN, 74 * rather than garbage. 75 * 76 * Honoring the flag in the way Linux does seems fraught. If we 77 * actually use the output of a random(4) implementation prior to 78 * seeding, we leak some entropy about the initial seed to attackers. 79 * This seems unacceptable -- it defeats the purpose of blocking on 80 * initial seeding. 81 * 82 * Secondary to that concern, before seeding we may have arbitrarily 83 * little entropy collected; producing output from zero or a handful of 84 * entropy bits does not seem particularly useful to userspace. 85 * 86 * If userspace can accept garbage, insecure non-random bytes, they can 87 * create their own insecure garbage with srandom(time(NULL)) or 88 * similar. Asking the kernel to produce it from the secure 89 * getrandom(2) API seems inane. 90 * 91 * We elect to emulate GRND_INSECURE as an alternative spelling of 92 * GRND_NONBLOCK (2). 93 */ 94 if ((flags & GRND_INSECURE) != 0) 95 flags |= GRND_NONBLOCK; 96 97 if (buflen == 0) { 98 td->td_retval[0] = 0; 99 return (0); 100 } 101 102 aiov.iov_base = user_buf; 103 aiov.iov_len = buflen; 104 auio.uio_iov = &aiov; 105 auio.uio_iovcnt = 1; 106 auio.uio_offset = 0; 107 auio.uio_resid = buflen; 108 auio.uio_segflg = UIO_USERSPACE; 109 auio.uio_rw = UIO_READ; 110 auio.uio_td = td; 111 112 error = read_random_uio(&auio, (flags & GRND_NONBLOCK) != 0); 113 if (error == 0) 114 td->td_retval[0] = buflen - auio.uio_resid; 115 return (error); 116 } 117 118 #ifndef _SYS_SYSPROTO_H_ 119 struct getrandom_args { 120 void *buf; 121 size_t buflen; 122 unsigned int flags; 123 }; 124 #endif 125 126 int 127 sys_getrandom(struct thread *td, struct getrandom_args *uap) 128 { 129 return (kern_getrandom(td, uap->buf, uap->buflen, uap->flags)); 130 } 131