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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: noise.c,v 1.5 1999/12/22 15:57:55 mdw Exp $ |
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4 | * |
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5 | * Acquisition of environmental noise (Unix-specific) |
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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 1.5 1999/12/22 15:57:55 mdw |
34 | * Label system-specific parts more clearly. |
35 | * |
c141f4b6 |
36 | * Revision 1.4 1999/12/10 23:25:15 mdw |
37 | * Bug fix: remove old spurious fflush. |
38 | * |
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39 | * Revision 1.3 1999/12/10 23:24:11 mdw |
40 | * Bug fix: flush buffers before forking. |
41 | * |
178220b3 |
42 | * Revision 1.2 1999/11/11 00:59:08 mdw |
43 | * A bit of reformatting. Initialize the uid and gid correctly. |
44 | * |
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45 | * Revision 1.1 1999/09/03 08:41:12 mdw |
46 | * Initial import. |
47 | * |
48 | */ |
49 | |
50 | /*----- Header files ------------------------------------------------------*/ |
51 | |
178220b3 |
52 | #include "config.h" |
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53 | |
54 | #include <stdio.h> |
55 | #include <string.h> |
56 | #include <signal.h> |
57 | |
58 | #include <sys/types.h> |
59 | #include <sys/time.h> |
60 | #include <sys/wait.h> |
61 | |
62 | #include <fcntl.h> |
63 | #include <unistd.h> |
64 | |
65 | #ifdef HAVE_SETGROUPS |
66 | # include <grp.h> |
67 | #endif |
68 | |
69 | #include <mLib/bits.h> |
70 | #include <mLib/tv.h> |
71 | |
72 | #include "noise.h" |
73 | #include "paranoia.h" |
74 | #include "rand.h" |
75 | |
76 | /*----- Magical numbers ---------------------------------------------------*/ |
77 | |
78 | #define NOISE_KIDLIFE 100000 /* @noise_filter@ child lifetime */ |
79 | #define MILLION 1000000 /* One million */ |
80 | |
81 | /*----- Noise source definition -------------------------------------------*/ |
82 | |
83 | rand_source noise_source = { noise_acquire, noise_timer }; |
84 | |
85 | /*----- Static variables --------------------------------------------------*/ |
86 | |
87 | /* --- Timer differences --- */ |
88 | |
89 | static unsigned long noise_last; /* Last time recorded */ |
90 | static unsigned long noise_diff; /* Last first order difference */ |
91 | |
92 | /* --- Setuid program handling --- */ |
93 | |
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94 | static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */ |
95 | static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */ |
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96 | |
97 | /*----- Main code ---------------------------------------------------------*/ |
98 | |
99 | /* --- @bitcount@ --- * |
100 | * |
101 | * Arguments: @unsigned long x@ = a word containing bits |
102 | * |
103 | * Returns: The number of bits set in the word. |
104 | */ |
105 | |
106 | static int bitcount(unsigned long x) |
107 | { |
108 | char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3, |
109 | 1, 2, 2, 3, 2, 3, 3, 4 }; |
110 | int count = 0; |
111 | while (x) { |
112 | count += ctab[x & 0xfu]; |
113 | x >>= 4; |
114 | } |
115 | return (count); |
116 | } |
117 | |
118 | /* --- @timer@ --- * |
119 | * |
120 | * Arguments: @rand_pool *r@ = pointer to randomness pool |
121 | * @struct timeval *tv@ = pointer to time block |
122 | * |
123 | * Returns: Nonzer if some randomness was contributed. |
124 | * |
125 | * Use: Low-level timer contributor. |
126 | */ |
127 | |
128 | static int timer(rand_pool *r, struct timeval *tv) |
129 | { |
130 | unsigned long x, d, dd; |
131 | int de, dde; |
132 | int ret; |
133 | |
134 | x = tv->tv_usec + MILLION * tv->tv_sec; |
135 | d = x ^ noise_last; |
136 | dd = d ^ noise_diff; |
137 | noise_diff = d; |
138 | de = bitcount(d); |
139 | dde = bitcount(dd); |
140 | rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde); |
141 | ret = (de || dde); |
142 | BURN(tv); x = d = dd = de = dde = 0; |
143 | return (ret); |
144 | } |
145 | |
146 | /* --- @noise_timer@ --- * |
147 | * |
148 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
149 | * |
150 | * Returns: Nonzero if some randomness was contributed. |
151 | * |
152 | * Use: Contributes the current time to the randomness pool. |
153 | * A guess at the number of useful bits contributed is made, |
154 | * based on first and second order bit differences. This isn't |
155 | * ever-so reliable, but it's better than nothing. |
156 | */ |
157 | |
158 | int noise_timer(rand_pool *r) |
159 | { |
160 | struct timeval tv; |
161 | gettimeofday(&tv, 0); |
162 | return (timer(r, &tv)); |
163 | } |
164 | |
165 | /* --- @noise_devrandom@ --- * |
166 | * |
167 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
168 | * |
169 | * Returns: Nonzero if some randomness was contributed. |
170 | * |
171 | * Use: Attempts to obtain some randomness from the system entropy |
172 | * pool. All bits from the device are assumed to be good. |
173 | */ |
174 | |
175 | int noise_devrandom(rand_pool *r) |
176 | { |
177 | int fd; |
178 | octet buf[RAND_POOLSZ]; |
179 | ssize_t len; |
180 | int ret = 0; |
181 | |
182 | /* --- Be nice to other clients of the random device --- * |
183 | * |
184 | * Attempt to open the device nonblockingly. If that works, take up to |
185 | * one bufferful and then close again. If there's no data to be read, |
186 | * then that's tough and we go away again, on the grounds that the device |
187 | * needs to get some more entropy from somewhere. |
188 | */ |
189 | |
190 | if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) { |
191 | if ((len = read(fd, buf, sizeof(buf))) > 0) { |
192 | rand_add(r, buf, len, len * 8); |
193 | BURN(buf); |
194 | ret = 1; |
195 | } |
196 | close(fd); |
197 | } |
198 | noise_timer(r); |
199 | return (ret); |
200 | } |
201 | |
202 | /* --- @noise_setid@ --- * |
203 | * |
204 | * Arguments: @uid_t uid@ = uid to set |
205 | * @gid_t gid@ = gid to set |
206 | * |
207 | * Returns: --- |
208 | * |
209 | * Use: Sets the user and group ids to be used by @noise_filter@ |
210 | * when running child processes. This is useful to avoid |
211 | * giving shell commands (even carefully written ones) undue |
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212 | * privileges. This interface is Unix-specific |
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213 | */ |
214 | |
215 | void noise_setid(uid_t uid, gid_t gid) |
216 | { |
217 | noise_uid = uid; |
218 | noise_gid = gid; |
219 | } |
220 | |
221 | /* --- @noise_filter@ --- * |
222 | * |
223 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
224 | * @int good@ = number of good bits per 1024 bits |
225 | * @const char *c@ = shell command to run |
226 | * |
227 | * Returns: Nonzero if some randomness was contributed. |
228 | * |
229 | * Use: Attempts to execute a shell command, and dump it into the |
230 | * randomness pool. A very rough estimate of the number of |
231 | * good bits is made, based on the size of the command's output. |
232 | * This function calls @waitpid@, so be careful. Before execing |
233 | * the command, the process uid and gid are set to the values |
234 | * given to @noise_setid@, and an attempt is made to reset the |
235 | * list of supplementary groups. The environment passed to |
236 | * the command has been severly lobotimized. If the command |
237 | * fails to complete within a short time period, it is killed. |
238 | * Paranoid use of close-on-exec flags for file descriptors is |
239 | * recommended. |
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240 | * |
241 | * This interface is Unix-specific. |
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242 | */ |
243 | |
244 | int noise_filter(rand_pool *r, int good, const char *c) |
245 | { |
246 | char buf[4096]; |
247 | pid_t kid; |
248 | int fd[2]; |
249 | struct timeval dead; |
250 | int ret = 0; |
251 | const char *env[] = { |
252 | "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc", |
253 | 0 |
254 | }; |
255 | |
256 | /* --- Remember when this business started --- */ |
257 | |
258 | gettimeofday(&dead, 0); |
259 | timer(r, &dead); |
260 | |
261 | /* --- Create a pipe --- */ |
262 | |
263 | if (pipe(fd)) |
264 | return (ret); |
265 | |
266 | /* --- Fork a child off --- */ |
267 | |
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268 | fflush(0); |
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269 | kid = fork(); |
270 | if (kid < 0) { |
271 | close(fd[0]); |
272 | close(fd[1]); |
273 | return (ret); |
274 | } |
275 | |
276 | /* --- Handle the child end of the deal --- */ |
277 | |
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278 | if (kid == 0) { |
279 | int f; |
280 | |
281 | /* --- Set the pipe as standard output, close standard input --- */ |
282 | |
283 | close(0); close(1); close(2); |
284 | |
285 | if (fd[1] != 1) { |
286 | if (dup2(fd[1], 1) < 0) _exit(127); |
287 | close(fd[1]); |
288 | } |
289 | |
290 | if ((f = open("/dev/null", O_RDONLY)) != 0 || |
291 | (f = open("/dev/null", O_WRONLY)) != 2) |
292 | _exit(127); |
293 | |
294 | /* --- Play games with uids --- */ |
295 | |
296 | if (noise_gid != NOISE_NOSETGID) { |
297 | setgid(noise_gid); |
298 | setegid(noise_gid); |
299 | #ifdef HAVE_SETGROUPS |
300 | setgroups(1, &noise_gid); |
301 | #endif |
302 | } |
303 | |
304 | if (noise_uid != NOISE_NOSETUID) { |
305 | setuid(noise_uid); |
306 | seteuid(noise_uid); |
307 | } |
308 | |
309 | /* --- Start the process up --- */ |
310 | |
311 | execle("/bin/sh", "-c", c, (char *)0, env); |
312 | _exit(127); |
313 | } |
314 | |
315 | /* --- Sort out my end of the deal --- */ |
316 | |
317 | close(fd[1]); |
318 | |
319 | /* --- Decide on the deadline --- */ |
320 | |
321 | TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE); |
322 | |
323 | /* --- Now read, and think --- */ |
324 | |
325 | for (;;) { |
326 | struct timeval now, diff; |
327 | fd_set rd; |
328 | |
329 | gettimeofday(&now, 0); |
330 | timer(r, &now); |
331 | if (TV_CMP(&now, >, &dead)) |
332 | break; |
333 | TV_SUB(&diff, &dead, &now); |
334 | |
335 | FD_ZERO(&rd); |
336 | FD_SET(fd[0], &rd); |
337 | |
338 | if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0) |
339 | break; |
340 | if (FD_ISSET(fd[0], &rd)) { |
341 | ssize_t sz; |
342 | int goodbits; |
343 | |
344 | if ((sz = read(fd[0], buf, sizeof(buf))) <= 0) |
345 | break; |
346 | goodbits = (sz * good) / 128; |
347 | rand_add(r, buf, sz, goodbits); |
348 | ret = 1; |
349 | } |
350 | } |
351 | |
352 | /* --- We've finished with it: kill the child process --- * |
353 | * |
354 | * This is morally questionable. On the other hand, I don't want to be |
355 | * held up in the @waitpid@ call if I can possibly help it. Maybe a |
356 | * double-fork is worth doing here. |
357 | */ |
358 | |
359 | close(fd[0]); |
360 | BURN(buf); |
361 | noise_timer(r); |
362 | kill(kid, SIGKILL); |
363 | waitpid(kid, 0, 0); |
364 | return (ret); |
365 | } |
366 | |
367 | /* --- @noise_acquire@ --- * |
368 | * |
369 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
370 | * |
371 | * Returns: --- |
372 | * |
373 | * Use: Acquires some randomness from somewhere. |
374 | */ |
375 | |
376 | void noise_acquire(rand_pool *r) |
377 | { |
378 | if (!noise_devrandom(r)) { |
379 | |
380 | /* --- Output of `ps' --- * |
381 | * |
382 | * This is a hopefully cheap way of getting a bit of noise. I'm guessing |
383 | * the good bit ratio based on about 90 bytes per line of output, and |
384 | * each line containing maybe 12 bits worth of interesting data. (Some |
385 | * quick experiments with gzip seem to bear this idea out.) So, 12 good |
386 | * bits per 90 bytes of output gives slightly more than 17 good bits per |
387 | * 1024 bits of output. So I'll be a pessimist and say 16 bits. |
388 | */ |
389 | |
390 | (void) |
391 | (noise_filter(r, 16, "ps alxww") || |
392 | noise_filter(r, 16, "ps -elf")); |
393 | |
394 | /* --- Output of `netstat' --- * |
395 | * |
396 | * Another possibly cheap way of getting noise. My output has about |
397 | * 72 bytes per line of output. My wild guesses are telling me that |
398 | * there are probably only about four good bits per line (gzip tells |
399 | * me there's six, but I want to underestimate). Four bits per 72 bytes |
400 | * is 7 good bits per 1024 bits of output. Pessimist that I am, I'll |
401 | * call it six. |
402 | */ |
403 | |
404 | noise_filter(r, 6, "netstat -n"); |
405 | } |
406 | } |
407 | |
408 | /*----- That's all, folks -------------------------------------------------*/ |