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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: noise.c,v 1.2 1999/11/11 00:59:08 mdw Exp $ |
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4 | * |
5 | * Acquisition of environmental noise (Unix specific) |
6 | * |
7 | * (c) 1998 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of Catacomb. |
13 | * |
14 | * Catacomb is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * Catacomb is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with Catacomb; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: noise.c,v $ |
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33 | * Revision 1.2 1999/11/11 00:59:08 mdw |
34 | * A bit of reformatting. Initialize the uid and gid correctly. |
35 | * |
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36 | * Revision 1.1 1999/09/03 08:41:12 mdw |
37 | * Initial import. |
38 | * |
39 | */ |
40 | |
41 | /*----- Header files ------------------------------------------------------*/ |
42 | |
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43 | #include "config.h" |
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44 | |
45 | #include <stdio.h> |
46 | #include <string.h> |
47 | #include <signal.h> |
48 | |
49 | #include <sys/types.h> |
50 | #include <sys/time.h> |
51 | #include <sys/wait.h> |
52 | |
53 | #include <fcntl.h> |
54 | #include <unistd.h> |
55 | |
56 | #ifdef HAVE_SETGROUPS |
57 | # include <grp.h> |
58 | #endif |
59 | |
60 | #include <mLib/bits.h> |
61 | #include <mLib/tv.h> |
62 | |
63 | #include "noise.h" |
64 | #include "paranoia.h" |
65 | #include "rand.h" |
66 | |
67 | /*----- Magical numbers ---------------------------------------------------*/ |
68 | |
69 | #define NOISE_KIDLIFE 100000 /* @noise_filter@ child lifetime */ |
70 | #define MILLION 1000000 /* One million */ |
71 | |
72 | /*----- Noise source definition -------------------------------------------*/ |
73 | |
74 | rand_source noise_source = { noise_acquire, noise_timer }; |
75 | |
76 | /*----- Static variables --------------------------------------------------*/ |
77 | |
78 | /* --- Timer differences --- */ |
79 | |
80 | static unsigned long noise_last; /* Last time recorded */ |
81 | static unsigned long noise_diff; /* Last first order difference */ |
82 | |
83 | /* --- Setuid program handling --- */ |
84 | |
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85 | static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */ |
86 | static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */ |
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87 | |
88 | /*----- Main code ---------------------------------------------------------*/ |
89 | |
90 | /* --- @bitcount@ --- * |
91 | * |
92 | * Arguments: @unsigned long x@ = a word containing bits |
93 | * |
94 | * Returns: The number of bits set in the word. |
95 | */ |
96 | |
97 | static int bitcount(unsigned long x) |
98 | { |
99 | char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3, |
100 | 1, 2, 2, 3, 2, 3, 3, 4 }; |
101 | int count = 0; |
102 | while (x) { |
103 | count += ctab[x & 0xfu]; |
104 | x >>= 4; |
105 | } |
106 | return (count); |
107 | } |
108 | |
109 | /* --- @timer@ --- * |
110 | * |
111 | * Arguments: @rand_pool *r@ = pointer to randomness pool |
112 | * @struct timeval *tv@ = pointer to time block |
113 | * |
114 | * Returns: Nonzer if some randomness was contributed. |
115 | * |
116 | * Use: Low-level timer contributor. |
117 | */ |
118 | |
119 | static int timer(rand_pool *r, struct timeval *tv) |
120 | { |
121 | unsigned long x, d, dd; |
122 | int de, dde; |
123 | int ret; |
124 | |
125 | x = tv->tv_usec + MILLION * tv->tv_sec; |
126 | d = x ^ noise_last; |
127 | dd = d ^ noise_diff; |
128 | noise_diff = d; |
129 | de = bitcount(d); |
130 | dde = bitcount(dd); |
131 | rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde); |
132 | ret = (de || dde); |
133 | BURN(tv); x = d = dd = de = dde = 0; |
134 | return (ret); |
135 | } |
136 | |
137 | /* --- @noise_timer@ --- * |
138 | * |
139 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
140 | * |
141 | * Returns: Nonzero if some randomness was contributed. |
142 | * |
143 | * Use: Contributes the current time to the randomness pool. |
144 | * A guess at the number of useful bits contributed is made, |
145 | * based on first and second order bit differences. This isn't |
146 | * ever-so reliable, but it's better than nothing. |
147 | */ |
148 | |
149 | int noise_timer(rand_pool *r) |
150 | { |
151 | struct timeval tv; |
152 | gettimeofday(&tv, 0); |
153 | return (timer(r, &tv)); |
154 | } |
155 | |
156 | /* --- @noise_devrandom@ --- * |
157 | * |
158 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
159 | * |
160 | * Returns: Nonzero if some randomness was contributed. |
161 | * |
162 | * Use: Attempts to obtain some randomness from the system entropy |
163 | * pool. All bits from the device are assumed to be good. |
164 | */ |
165 | |
166 | int noise_devrandom(rand_pool *r) |
167 | { |
168 | int fd; |
169 | octet buf[RAND_POOLSZ]; |
170 | ssize_t len; |
171 | int ret = 0; |
172 | |
173 | /* --- Be nice to other clients of the random device --- * |
174 | * |
175 | * Attempt to open the device nonblockingly. If that works, take up to |
176 | * one bufferful and then close again. If there's no data to be read, |
177 | * then that's tough and we go away again, on the grounds that the device |
178 | * needs to get some more entropy from somewhere. |
179 | */ |
180 | |
181 | if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) { |
182 | if ((len = read(fd, buf, sizeof(buf))) > 0) { |
183 | rand_add(r, buf, len, len * 8); |
184 | BURN(buf); |
185 | ret = 1; |
186 | } |
187 | close(fd); |
188 | } |
189 | noise_timer(r); |
190 | return (ret); |
191 | } |
192 | |
193 | /* --- @noise_setid@ --- * |
194 | * |
195 | * Arguments: @uid_t uid@ = uid to set |
196 | * @gid_t gid@ = gid to set |
197 | * |
198 | * Returns: --- |
199 | * |
200 | * Use: Sets the user and group ids to be used by @noise_filter@ |
201 | * when running child processes. This is useful to avoid |
202 | * giving shell commands (even carefully written ones) undue |
203 | * privileges. |
204 | */ |
205 | |
206 | void noise_setid(uid_t uid, gid_t gid) |
207 | { |
208 | noise_uid = uid; |
209 | noise_gid = gid; |
210 | } |
211 | |
212 | /* --- @noise_filter@ --- * |
213 | * |
214 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
215 | * @int good@ = number of good bits per 1024 bits |
216 | * @const char *c@ = shell command to run |
217 | * |
218 | * Returns: Nonzero if some randomness was contributed. |
219 | * |
220 | * Use: Attempts to execute a shell command, and dump it into the |
221 | * randomness pool. A very rough estimate of the number of |
222 | * good bits is made, based on the size of the command's output. |
223 | * This function calls @waitpid@, so be careful. Before execing |
224 | * the command, the process uid and gid are set to the values |
225 | * given to @noise_setid@, and an attempt is made to reset the |
226 | * list of supplementary groups. The environment passed to |
227 | * the command has been severly lobotimized. If the command |
228 | * fails to complete within a short time period, it is killed. |
229 | * Paranoid use of close-on-exec flags for file descriptors is |
230 | * recommended. |
231 | */ |
232 | |
233 | int noise_filter(rand_pool *r, int good, const char *c) |
234 | { |
235 | char buf[4096]; |
236 | pid_t kid; |
237 | int fd[2]; |
238 | struct timeval dead; |
239 | int ret = 0; |
240 | const char *env[] = { |
241 | "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc", |
242 | 0 |
243 | }; |
244 | |
245 | /* --- Remember when this business started --- */ |
246 | |
247 | gettimeofday(&dead, 0); |
248 | timer(r, &dead); |
249 | |
250 | /* --- Create a pipe --- */ |
251 | |
252 | if (pipe(fd)) |
253 | return (ret); |
254 | |
255 | /* --- Fork a child off --- */ |
256 | |
257 | kid = fork(); |
258 | if (kid < 0) { |
259 | close(fd[0]); |
260 | close(fd[1]); |
261 | return (ret); |
262 | } |
263 | |
264 | /* --- Handle the child end of the deal --- */ |
265 | |
266 | fflush(0); |
267 | if (kid == 0) { |
268 | int f; |
269 | |
270 | /* --- Set the pipe as standard output, close standard input --- */ |
271 | |
272 | close(0); close(1); close(2); |
273 | |
274 | if (fd[1] != 1) { |
275 | if (dup2(fd[1], 1) < 0) _exit(127); |
276 | close(fd[1]); |
277 | } |
278 | |
279 | if ((f = open("/dev/null", O_RDONLY)) != 0 || |
280 | (f = open("/dev/null", O_WRONLY)) != 2) |
281 | _exit(127); |
282 | |
283 | /* --- Play games with uids --- */ |
284 | |
285 | if (noise_gid != NOISE_NOSETGID) { |
286 | setgid(noise_gid); |
287 | setegid(noise_gid); |
288 | #ifdef HAVE_SETGROUPS |
289 | setgroups(1, &noise_gid); |
290 | #endif |
291 | } |
292 | |
293 | if (noise_uid != NOISE_NOSETUID) { |
294 | setuid(noise_uid); |
295 | seteuid(noise_uid); |
296 | } |
297 | |
298 | /* --- Start the process up --- */ |
299 | |
300 | execle("/bin/sh", "-c", c, (char *)0, env); |
301 | _exit(127); |
302 | } |
303 | |
304 | /* --- Sort out my end of the deal --- */ |
305 | |
306 | close(fd[1]); |
307 | |
308 | /* --- Decide on the deadline --- */ |
309 | |
310 | TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE); |
311 | |
312 | /* --- Now read, and think --- */ |
313 | |
314 | for (;;) { |
315 | struct timeval now, diff; |
316 | fd_set rd; |
317 | |
318 | gettimeofday(&now, 0); |
319 | timer(r, &now); |
320 | if (TV_CMP(&now, >, &dead)) |
321 | break; |
322 | TV_SUB(&diff, &dead, &now); |
323 | |
324 | FD_ZERO(&rd); |
325 | FD_SET(fd[0], &rd); |
326 | |
327 | if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0) |
328 | break; |
329 | if (FD_ISSET(fd[0], &rd)) { |
330 | ssize_t sz; |
331 | int goodbits; |
332 | |
333 | if ((sz = read(fd[0], buf, sizeof(buf))) <= 0) |
334 | break; |
335 | goodbits = (sz * good) / 128; |
336 | rand_add(r, buf, sz, goodbits); |
337 | ret = 1; |
338 | } |
339 | } |
340 | |
341 | /* --- We've finished with it: kill the child process --- * |
342 | * |
343 | * This is morally questionable. On the other hand, I don't want to be |
344 | * held up in the @waitpid@ call if I can possibly help it. Maybe a |
345 | * double-fork is worth doing here. |
346 | */ |
347 | |
348 | close(fd[0]); |
349 | BURN(buf); |
350 | noise_timer(r); |
351 | kill(kid, SIGKILL); |
352 | waitpid(kid, 0, 0); |
353 | return (ret); |
354 | } |
355 | |
356 | /* --- @noise_acquire@ --- * |
357 | * |
358 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
359 | * |
360 | * Returns: --- |
361 | * |
362 | * Use: Acquires some randomness from somewhere. |
363 | */ |
364 | |
365 | void noise_acquire(rand_pool *r) |
366 | { |
367 | if (!noise_devrandom(r)) { |
368 | |
369 | /* --- Output of `ps' --- * |
370 | * |
371 | * This is a hopefully cheap way of getting a bit of noise. I'm guessing |
372 | * the good bit ratio based on about 90 bytes per line of output, and |
373 | * each line containing maybe 12 bits worth of interesting data. (Some |
374 | * quick experiments with gzip seem to bear this idea out.) So, 12 good |
375 | * bits per 90 bytes of output gives slightly more than 17 good bits per |
376 | * 1024 bits of output. So I'll be a pessimist and say 16 bits. |
377 | */ |
378 | |
379 | (void) |
380 | (noise_filter(r, 16, "ps alxww") || |
381 | noise_filter(r, 16, "ps -elf")); |
382 | |
383 | /* --- Output of `netstat' --- * |
384 | * |
385 | * Another possibly cheap way of getting noise. My output has about |
386 | * 72 bytes per line of output. My wild guesses are telling me that |
387 | * there are probably only about four good bits per line (gzip tells |
388 | * me there's six, but I want to underestimate). Four bits per 72 bytes |
389 | * is 7 good bits per 1024 bits of output. Pessimist that I am, I'll |
390 | * call it six. |
391 | */ |
392 | |
393 | noise_filter(r, 6, "netstat -n"); |
394 | } |
395 | } |
396 | |
397 | /*----- That's all, folks -------------------------------------------------*/ |