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/param.h> 30 #include <sys/errno.h> 31 #include <sys/limits.h> 32 #include <sys/proc.h> 33 #include <sys/random.h> 34 #include <sys/sysproto.h> 35 #include <sys/systm.h> 36 #include <sys/uio.h> 37 38 #define GRND_VALIDFLAGS (GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE) 39 40 /* 41 * read_random_uio(9) returns EWOULDBLOCK if a nonblocking request would block, 42 * but the Linux API name is EAGAIN. On FreeBSD, they have the same numeric 43 * value for now. 44 */ 45 CTASSERT(EWOULDBLOCK == EAGAIN); 46 47 static int 48 kern_getrandom(struct thread *td, void *user_buf, size_t buflen, 49 unsigned int flags) 50 { 51 struct uio auio; 52 struct iovec aiov; 53 int error; 54 55 if ((flags & ~GRND_VALIDFLAGS) != 0) 56 return (EINVAL); 57 if (buflen > IOSIZE_MAX) 58 return (EINVAL); 59 60 /* 61 * Linux compatibility: We have two choices for handling Linux's 62 * GRND_INSECURE. 63 * 64 * 1. We could ignore it completely (like GRND_RANDOM). However, this 65 * might produce the surprising result of GRND_INSECURE requests 66 * blocking, when the Linux API does not block. 67 * 68 * 2. Alternatively, we could treat GRND_INSECURE requests as requests 69 * for GRND_NONBLOCK. Here, the surprising result for Linux programs 70 * is that invocations with unseeded random(4) will produce EAGAIN, 71 * rather than garbage. 72 * 73 * Honoring the flag in the way Linux does seems fraught. If we 74 * actually use the output of a random(4) implementation prior to 75 * seeding, we leak some entropy about the initial seed to attackers. 76 * This seems unacceptable -- it defeats the purpose of blocking on 77 * initial seeding. 78 * 79 * Secondary to that concern, before seeding we may have arbitrarily 80 * little entropy collected; producing output from zero or a handful of 81 * entropy bits does not seem particularly useful to userspace. 82 * 83 * If userspace can accept garbage, insecure non-random bytes, they can 84 * create their own insecure garbage with srandom(time(NULL)) or 85 * similar. Asking the kernel to produce it from the secure 86 * getrandom(2) API seems inane. 87 * 88 * We elect to emulate GRND_INSECURE as an alternative spelling of 89 * GRND_NONBLOCK (2). 90 */ 91 if ((flags & GRND_INSECURE) != 0) 92 flags |= GRND_NONBLOCK; 93 94 if (buflen == 0) { 95 td->td_retval[0] = 0; 96 return (0); 97 } 98 99 aiov.iov_base = user_buf; 100 aiov.iov_len = buflen; 101 auio.uio_iov = &aiov; 102 auio.uio_iovcnt = 1; 103 auio.uio_offset = 0; 104 auio.uio_resid = buflen; 105 auio.uio_segflg = UIO_USERSPACE; 106 auio.uio_rw = UIO_READ; 107 auio.uio_td = td; 108 109 error = read_random_uio(&auio, (flags & GRND_NONBLOCK) != 0); 110 if (error == 0) 111 td->td_retval[0] = buflen - auio.uio_resid; 112 return (error); 113 } 114 115 #ifndef _SYS_SYSPROTO_H_ 116 struct getrandom_args { 117 void *buf; 118 size_t buflen; 119 unsigned int flags; 120 }; 121 #endif 122 123 int 124 sys_getrandom(struct thread *td, struct getrandom_args *uap) 125 { 126 return (kern_getrandom(td, uap->buf, uap->buflen, uap->flags)); 127 } 128