sys_getrandom.c (6469bdcdb6a5968dc7edfcfb495d427b4bfdb3dd) sys_getrandom.c (86def3dcd66af169aac0c6ff91dd94a98369cc89)
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

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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
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

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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)
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 */
48CTASSERT(EWOULDBLOCK == EAGAIN);
49

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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
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 */
48CTASSERT(EWOULDBLOCK == EAGAIN);
49

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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
63 if (buflen == 0) {
64 td->td_retval[0] = 0;
65 return (0);
66 }
67
68 aiov.iov_base = user_buf;
69 aiov.iov_len = buflen;
70 auio.uio_iov = &aiov;

--- 26 unchanged lines hidden --- 		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;

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