1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 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 #include <sys/param.h> 31 #include <sys/errno.h> 32 #include <sys/limits.h> 33 #include <sys/proc.h> 34 #include <sys/random.h> 35 #include <sys/sysproto.h> 36 #include <sys/systm.h> 37 #include <sys/uio.h> 38 39 #define GRND_VALIDFLAGS (GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE) 40 41 /* 42 * read_random_uio(9) returns EWOULDBLOCK if a nonblocking request would block, 43 * but the Linux API name is EAGAIN. On FreeBSD, they have the same numeric 44 * value for now. 45 */ 46 CTASSERT(EWOULDBLOCK == EAGAIN); 47 48 static int 49 kern_getrandom(struct thread *td, void *user_buf, size_t buflen, 50 unsigned int flags) 51 { 52 struct uio auio; 53 struct iovec aiov; 54 int error; 55 56 if ((flags & ~GRND_VALIDFLAGS) != 0) 57 return (EINVAL); 58 if (buflen > IOSIZE_MAX) 59 return (EINVAL); 60 61 /* 62 * Linux compatibility: We have two choices for handling Linux's 63 * GRND_INSECURE. 64 * 65 * 1. We could ignore it completely (like GRND_RANDOM). However, this 66 * might produce the surprising result of GRND_INSECURE requests 67 * blocking, when the Linux API does not block. 68 * 69 * 2. Alternatively, we could treat GRND_INSECURE requests as requests 70 * for GRND_NONBLOCK. Here, the surprising result for Linux programs 71 * is that invocations with unseeded random(4) will produce EAGAIN, 72 * rather than garbage. 73 * 74 * Honoring the flag in the way Linux does seems fraught. If we 75 * actually use the output of a random(4) implementation prior to 76 * seeding, we leak some entropy about the initial seed to attackers. 77 * This seems unacceptable -- it defeats the purpose of blocking on 78 * initial seeding. 79 * 80 * Secondary to that concern, before seeding we may have arbitrarily 81 * little entropy collected; producing output from zero or a handful of 82 * entropy bits does not seem particularly useful to userspace. 83 * 84 * If userspace can accept garbage, insecure non-random bytes, they can 85 * create their own insecure garbage with srandom(time(NULL)) or 86 * similar. Asking the kernel to produce it from the secure 87 * getrandom(2) API seems inane. 88 * 89 * We elect to emulate GRND_INSECURE as an alternative spelling of 90 * GRND_NONBLOCK (2). 91 */ 92 if ((flags & GRND_INSECURE) != 0) 93 flags |= GRND_NONBLOCK; 94 95 if (buflen == 0) { 96 td->td_retval[0] = 0; 97 return (0); 98 } 99 100 aiov.iov_base = user_buf; 101 aiov.iov_len = buflen; 102 auio.uio_iov = &aiov; 103 auio.uio_iovcnt = 1; 104 auio.uio_offset = 0; 105 auio.uio_resid = buflen; 106 auio.uio_segflg = UIO_USERSPACE; 107 auio.uio_rw = UIO_READ; 108 auio.uio_td = td; 109 110 error = read_random_uio(&auio, (flags & GRND_NONBLOCK) != 0); 111 if (error == 0) 112 td->td_retval[0] = buflen - auio.uio_resid; 113 return (error); 114 } 115 116 #ifndef _SYS_SYSPROTO_H_ 117 struct getrandom_args { 118 void *buf; 119 size_t buflen; 120 unsigned int flags; 121 }; 122 #endif 123 124 int 125 sys_getrandom(struct thread *td, struct getrandom_args *uap) 126 { 127 return (kern_getrandom(td, uap->buf, uap->buflen, uap->flags)); 128 } 129