xref: /freebsd/crypto/openssh/entropy.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*
2  * Copyright (c) 2001 Damien Miller.  All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23  */
24 
25 #include "includes.h"
26 
27 #include <sys/types.h>
28 #include <sys/wait.h>
29 
30 #ifdef HAVE_SYS_STAT_H
31 # include <sys/stat.h>
32 #endif
33 
34 #ifdef HAVE_FCNTL_H
35 # include <fcntl.h>
36 #endif
37 #include <stdarg.h>
38 #include <unistd.h>
39 #include <signal.h>
40 
41 #include <openssl/rand.h>
42 #include <openssl/crypto.h>
43 #include <openssl/err.h>
44 
45 #include "ssh.h"
46 #include "misc.h"
47 #include "xmalloc.h"
48 #include "atomicio.h"
49 #include "pathnames.h"
50 #include "log.h"
51 #include "buffer.h"
52 
53 /*
54  * Portable OpenSSH PRNG seeding:
55  * If OpenSSL has not "internally seeded" itself (e.g. pulled data from
56  * /dev/random), then we execute a "ssh-rand-helper" program which
57  * collects entropy and writes it to stdout. The child program must
58  * write at least RANDOM_SEED_SIZE bytes. The child is run with stderr
59  * attached, so error/debugging output should be visible.
60  *
61  * XXX: we should tell the child how many bytes we need.
62  */
63 
64 #ifndef OPENSSL_PRNG_ONLY
65 #define RANDOM_SEED_SIZE 48
66 static uid_t original_uid, original_euid;
67 #endif
68 
69 void
70 seed_rng(void)
71 {
72 #ifndef OPENSSL_PRNG_ONLY
73 	int devnull;
74 	int p[2];
75 	pid_t pid;
76 	int ret;
77 	unsigned char buf[RANDOM_SEED_SIZE];
78 	mysig_t old_sigchld;
79 
80 	if (RAND_status() == 1) {
81 		debug3("RNG is ready, skipping seeding");
82 		return;
83 	}
84 
85 	debug3("Seeding PRNG from %s", SSH_RAND_HELPER);
86 
87 	if ((devnull = open("/dev/null", O_RDWR)) == -1)
88 		fatal("Couldn't open /dev/null: %s", strerror(errno));
89 	if (pipe(p) == -1)
90 		fatal("pipe: %s", strerror(errno));
91 
92 	old_sigchld = signal(SIGCHLD, SIG_DFL);
93 	if ((pid = fork()) == -1)
94 		fatal("Couldn't fork: %s", strerror(errno));
95 	if (pid == 0) {
96 		dup2(devnull, STDIN_FILENO);
97 		dup2(p[1], STDOUT_FILENO);
98 		/* Keep stderr open for errors */
99 		close(p[0]);
100 		close(p[1]);
101 		close(devnull);
102 
103 		if (original_uid != original_euid &&
104 		    ( seteuid(getuid()) == -1 ||
105 		      setuid(original_uid) == -1) ) {
106 			fprintf(stderr, "(rand child) setuid(%li): %s\n",
107 			    (long int)original_uid, strerror(errno));
108 			_exit(1);
109 		}
110 
111 		execl(SSH_RAND_HELPER, "ssh-rand-helper", NULL);
112 		fprintf(stderr, "(rand child) Couldn't exec '%s': %s\n",
113 		    SSH_RAND_HELPER, strerror(errno));
114 		_exit(1);
115 	}
116 
117 	close(devnull);
118 	close(p[1]);
119 
120 	memset(buf, '\0', sizeof(buf));
121 	ret = atomicio(read, p[0], buf, sizeof(buf));
122 	if (ret == -1)
123 		fatal("Couldn't read from ssh-rand-helper: %s",
124 		    strerror(errno));
125 	if (ret != sizeof(buf))
126 		fatal("ssh-rand-helper child produced insufficient data");
127 
128 	close(p[0]);
129 
130 	if (waitpid(pid, &ret, 0) == -1)
131 		fatal("Couldn't wait for ssh-rand-helper completion: %s",
132 		    strerror(errno));
133 	signal(SIGCHLD, old_sigchld);
134 
135 	/* We don't mind if the child exits upon a SIGPIPE */
136 	if (!WIFEXITED(ret) &&
137 	    (!WIFSIGNALED(ret) || WTERMSIG(ret) != SIGPIPE))
138 		fatal("ssh-rand-helper terminated abnormally");
139 	if (WEXITSTATUS(ret) != 0)
140 		fatal("ssh-rand-helper exit with exit status %d", ret);
141 
142 	RAND_add(buf, sizeof(buf), sizeof(buf));
143 	memset(buf, '\0', sizeof(buf));
144 
145 #endif /* OPENSSL_PRNG_ONLY */
146 	if (RAND_status() != 1)
147 		fatal("PRNG is not seeded");
148 }
149 
150 void
151 init_rng(void)
152 {
153 	/*
154 	 * OpenSSL version numbers: MNNFFPPS: major minor fix patch status
155 	 * We match major, minor, fix and status (not patch)
156 	 */
157 	if ((SSLeay() ^ OPENSSL_VERSION_NUMBER) & ~0xff0L)
158 		fatal("OpenSSL version mismatch. Built against %lx, you "
159 		    "have %lx", OPENSSL_VERSION_NUMBER, SSLeay());
160 
161 #ifndef OPENSSL_PRNG_ONLY
162 	original_uid = getuid();
163 	original_euid = geteuid();
164 #endif
165 }
166 
167 #ifndef OPENSSL_PRNG_ONLY
168 void
169 rexec_send_rng_seed(Buffer *m)
170 {
171 	u_char buf[RANDOM_SEED_SIZE];
172 
173 	if (RAND_bytes(buf, sizeof(buf)) <= 0) {
174 		error("Couldn't obtain random bytes (error %ld)",
175 		    ERR_get_error());
176 		buffer_put_string(m, "", 0);
177 	} else
178 		buffer_put_string(m, buf, sizeof(buf));
179 }
180 
181 void
182 rexec_recv_rng_seed(Buffer *m)
183 {
184 	u_char *buf;
185 	u_int len;
186 
187 	buf = buffer_get_string_ret(m, &len);
188 	if (buf != NULL) {
189 		debug3("rexec_recv_rng_seed: seeding rng with %u bytes", len);
190 		RAND_add(buf, len, len);
191 	}
192 }
193 #endif
194