summaryrefslogtreecommitdiff
path: root/entropy.c
blob: da1a391f3f066bd8d4a84204eca5881663fdd344 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
/*
 * Copyright (c) 2001 Damien Miller.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <openssl/rand.h>
#include <openssl/crypto.h>

#include "ssh.h"
#include "misc.h"
#include "xmalloc.h"
#include "atomicio.h"
#include "pathnames.h"
#include "log.h"

/*
 * Portable OpenSSH PRNG seeding:
 * If OpenSSL has not "internally seeded" itself (e.g. pulled data from 
 * /dev/random), then we execute a "ssh-rand-helper" program which 
 * collects entropy and writes it to stdout. The child program must 
 * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
 * attached, so error/debugging output should be visible.
 *
 * XXX: we should tell the child how many bytes we need.
 */

RCSID("$Id: entropy.c,v 1.43 2002/04/21 18:26:10 tim Exp $");

#ifndef OPENSSL_PRNG_ONLY
#define RANDOM_SEED_SIZE 48
static uid_t original_uid, original_euid;
#endif

void
seed_rng(void)
{
#ifndef OPENSSL_PRNG_ONLY
	int devnull;
	int p[2];
	pid_t pid;
	int ret;
	unsigned char buf[RANDOM_SEED_SIZE];
	mysig_t old_sigchld;

	if (RAND_status() == 1) {
		debug3("RNG is ready, skipping seeding");
		return;
	}

	debug3("Seeding PRNG from %s", SSH_RAND_HELPER);

	if ((devnull = open("/dev/null", O_RDWR)) == -1)
		fatal("Couldn't open /dev/null: %s", strerror(errno));
	if (pipe(p) == -1)
		fatal("pipe: %s", strerror(errno));

	old_sigchld = mysignal(SIGCHLD, SIG_DFL);
	if ((pid = fork()) == -1)
		fatal("Couldn't fork: %s", strerror(errno));
	if (pid == 0) {
		dup2(devnull, STDIN_FILENO);
		dup2(p[1], STDOUT_FILENO);
		/* Keep stderr open for errors */
		close(p[0]);
		close(p[1]);
		close(devnull);

		if (original_uid != original_euid && 
		    ( seteuid(getuid()) == -1 || 
		      setuid(original_uid) == -1) ) {
			fprintf(stderr, "(rand child) setuid(%d): %s\n", 
			    original_uid, strerror(errno));
			_exit(1);
		}
		
		execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
		fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n", 
		    SSH_RAND_HELPER, strerror(errno));
		_exit(1);
	}

	close(devnull);
	close(p[1]);

	memset(buf, '\0', sizeof(buf));
	ret = atomicio(read, p[0], buf, sizeof(buf));
	if (ret == -1)
		fatal("Couldn't read from ssh-rand-helper: %s",
		    strerror(errno));
	if (ret != sizeof(buf))
		fatal("ssh-rand-helper child produced insufficient data");

	close(p[0]);

	if (waitpid(pid, &ret, 0) == -1)
	       fatal("Couldn't wait for ssh-rand-helper completion: %s", 
	           strerror(errno));
	mysignal(SIGCHLD, old_sigchld);

	/* We don't mind if the child exits upon a SIGPIPE */
	if (!WIFEXITED(ret) && 
	    (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
		fatal("ssh-rand-helper terminated abnormally");
	if (WEXITSTATUS(ret) != 0)
		fatal("ssh-rand-helper exit with exit status %d", ret);

	RAND_add(buf, sizeof(buf), sizeof(buf));
	memset(buf, '\0', sizeof(buf));

#endif /* OPENSSL_PRNG_ONLY */
	if (RAND_status() != 1)
		fatal("PRNG is not seeded");
}

void
init_rng(void) 
{
	/*
	 * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
	 * We match major, minor, fix and status (not patch)
	 */
	if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
		fatal("OpenSSL version mismatch. Built against %lx, you "
		    "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());

#ifndef OPENSSL_PRNG_ONLY
	if ((original_uid = getuid()) == -1)
		fatal("getuid: %s", strerror(errno));
	if ((original_euid = geteuid()) == -1)
		fatal("geteuid: %s", strerror(errno));
#endif
}