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1 | /* -*-c-*- |
2 | * |
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3 | * $Id$ |
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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 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
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32 | #include "config.h" |
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33 | |
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34 | #include <setjmp.h> |
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35 | #include <stdio.h> |
36 | #include <string.h> |
37 | #include <signal.h> |
38 | |
39 | #include <sys/types.h> |
40 | #include <sys/time.h> |
41 | #include <sys/wait.h> |
42 | |
43 | #include <fcntl.h> |
44 | #include <unistd.h> |
45 | |
46 | #ifdef HAVE_SETGROUPS |
47 | # include <grp.h> |
48 | #endif |
49 | |
50 | #include <mLib/bits.h> |
51 | #include <mLib/tv.h> |
52 | |
53 | #include "noise.h" |
54 | #include "paranoia.h" |
55 | #include "rand.h" |
56 | |
57 | /*----- Magical numbers ---------------------------------------------------*/ |
58 | |
59 | #define NOISE_KIDLIFE 100000 /* @noise_filter@ child lifetime */ |
60 | #define MILLION 1000000 /* One million */ |
61 | |
62 | /*----- Noise source definition -------------------------------------------*/ |
63 | |
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64 | const rand_source noise_source = { noise_acquire, noise_timer }; |
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65 | |
66 | /*----- Static variables --------------------------------------------------*/ |
67 | |
68 | /* --- Timer differences --- */ |
69 | |
70 | static unsigned long noise_last; /* Last time recorded */ |
71 | static unsigned long noise_diff; /* Last first order difference */ |
72 | |
73 | /* --- Setuid program handling --- */ |
74 | |
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75 | static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */ |
76 | static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */ |
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77 | |
78 | /*----- Main code ---------------------------------------------------------*/ |
79 | |
80 | /* --- @bitcount@ --- * |
81 | * |
82 | * Arguments: @unsigned long x@ = a word containing bits |
83 | * |
84 | * Returns: The number of bits set in the word. |
85 | */ |
86 | |
87 | static int bitcount(unsigned long x) |
88 | { |
89 | char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3, |
90 | 1, 2, 2, 3, 2, 3, 3, 4 }; |
91 | int count = 0; |
92 | while (x) { |
93 | count += ctab[x & 0xfu]; |
94 | x >>= 4; |
95 | } |
96 | return (count); |
97 | } |
98 | |
99 | /* --- @timer@ --- * |
100 | * |
101 | * Arguments: @rand_pool *r@ = pointer to randomness pool |
102 | * @struct timeval *tv@ = pointer to time block |
103 | * |
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104 | * Returns: Nonzero if some randomness was contributed. |
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105 | * |
106 | * Use: Low-level timer contributor. |
107 | */ |
108 | |
109 | static int timer(rand_pool *r, struct timeval *tv) |
110 | { |
111 | unsigned long x, d, dd; |
112 | int de, dde; |
113 | int ret; |
114 | |
115 | x = tv->tv_usec + MILLION * tv->tv_sec; |
116 | d = x ^ noise_last; |
117 | dd = d ^ noise_diff; |
118 | noise_diff = d; |
119 | de = bitcount(d); |
120 | dde = bitcount(dd); |
121 | rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde); |
122 | ret = (de || dde); |
123 | BURN(tv); x = d = dd = de = dde = 0; |
124 | return (ret); |
125 | } |
126 | |
127 | /* --- @noise_timer@ --- * |
128 | * |
129 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
130 | * |
131 | * Returns: Nonzero if some randomness was contributed. |
132 | * |
133 | * Use: Contributes the current time to the randomness pool. |
134 | * A guess at the number of useful bits contributed is made, |
135 | * based on first and second order bit differences. This isn't |
136 | * ever-so reliable, but it's better than nothing. |
137 | */ |
138 | |
139 | int noise_timer(rand_pool *r) |
140 | { |
141 | struct timeval tv; |
142 | gettimeofday(&tv, 0); |
143 | return (timer(r, &tv)); |
144 | } |
145 | |
146 | /* --- @noise_devrandom@ --- * |
147 | * |
148 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
149 | * |
150 | * Returns: Nonzero if some randomness was contributed. |
151 | * |
152 | * Use: Attempts to obtain some randomness from the system entropy |
153 | * pool. All bits from the device are assumed to be good. |
154 | */ |
155 | |
156 | int noise_devrandom(rand_pool *r) |
157 | { |
158 | int fd; |
159 | octet buf[RAND_POOLSZ]; |
160 | ssize_t len; |
161 | int ret = 0; |
162 | |
163 | /* --- Be nice to other clients of the random device --- * |
164 | * |
165 | * Attempt to open the device nonblockingly. If that works, take up to |
166 | * one bufferful and then close again. If there's no data to be read, |
167 | * then that's tough and we go away again, on the grounds that the device |
168 | * needs to get some more entropy from somewhere. |
169 | */ |
170 | |
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171 | if ((fd = open("/dev/urandom", O_RDONLY | O_NONBLOCK)) >= 0 || |
172 | (fd = open("/dev/arandom", O_RDONLY | O_NONBLOCK)) >= 0 || |
173 | (fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) { |
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174 | if ((len = read(fd, buf, sizeof(buf))) > 0) { |
175 | rand_add(r, buf, len, len * 8); |
176 | BURN(buf); |
177 | ret = 1; |
178 | } |
179 | close(fd); |
180 | } |
181 | noise_timer(r); |
182 | return (ret); |
183 | } |
184 | |
185 | /* --- @noise_setid@ --- * |
186 | * |
187 | * Arguments: @uid_t uid@ = uid to set |
188 | * @gid_t gid@ = gid to set |
189 | * |
190 | * Returns: --- |
191 | * |
192 | * Use: Sets the user and group ids to be used by @noise_filter@ |
193 | * when running child processes. This is useful to avoid |
194 | * giving shell commands (even carefully written ones) undue |
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195 | * privileges. This interface is Unix-specific |
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196 | */ |
197 | |
198 | void noise_setid(uid_t uid, gid_t gid) |
199 | { |
200 | noise_uid = uid; |
201 | noise_gid = gid; |
202 | } |
203 | |
204 | /* --- @noise_filter@ --- * |
205 | * |
206 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
207 | * @int good@ = number of good bits per 1024 bits |
208 | * @const char *c@ = shell command to run |
209 | * |
210 | * Returns: Nonzero if some randomness was contributed. |
211 | * |
212 | * Use: Attempts to execute a shell command, and dump it into the |
213 | * randomness pool. A very rough estimate of the number of |
214 | * good bits is made, based on the size of the command's output. |
215 | * This function calls @waitpid@, so be careful. Before execing |
216 | * the command, the process uid and gid are set to the values |
217 | * given to @noise_setid@, and an attempt is made to reset the |
218 | * list of supplementary groups. The environment passed to |
219 | * the command has been severly lobotimized. If the command |
220 | * fails to complete within a short time period, it is killed. |
221 | * Paranoid use of close-on-exec flags for file descriptors is |
222 | * recommended. |
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223 | * |
224 | * This interface is Unix-specific. |
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225 | */ |
226 | |
227 | int noise_filter(rand_pool *r, int good, const char *c) |
228 | { |
229 | char buf[4096]; |
230 | pid_t kid; |
231 | int fd[2]; |
232 | struct timeval dead; |
233 | int ret = 0; |
234 | const char *env[] = { |
235 | "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc", |
236 | 0 |
237 | }; |
238 | |
239 | /* --- Remember when this business started --- */ |
240 | |
241 | gettimeofday(&dead, 0); |
242 | timer(r, &dead); |
243 | |
244 | /* --- Create a pipe --- */ |
245 | |
246 | if (pipe(fd)) |
247 | return (ret); |
248 | |
249 | /* --- Fork a child off --- */ |
250 | |
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251 | fflush(0); |
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252 | kid = fork(); |
253 | if (kid < 0) { |
254 | close(fd[0]); |
255 | close(fd[1]); |
256 | return (ret); |
257 | } |
258 | |
259 | /* --- Handle the child end of the deal --- */ |
260 | |
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261 | if (kid == 0) { |
262 | int f; |
263 | |
264 | /* --- Set the pipe as standard output, close standard input --- */ |
265 | |
266 | close(0); close(1); close(2); |
267 | |
268 | if (fd[1] != 1) { |
269 | if (dup2(fd[1], 1) < 0) _exit(127); |
270 | close(fd[1]); |
271 | } |
272 | |
273 | if ((f = open("/dev/null", O_RDONLY)) != 0 || |
274 | (f = open("/dev/null", O_WRONLY)) != 2) |
275 | _exit(127); |
276 | |
277 | /* --- Play games with uids --- */ |
278 | |
279 | if (noise_gid != NOISE_NOSETGID) { |
280 | setgid(noise_gid); |
281 | setegid(noise_gid); |
282 | #ifdef HAVE_SETGROUPS |
283 | setgroups(1, &noise_gid); |
284 | #endif |
285 | } |
286 | |
287 | if (noise_uid != NOISE_NOSETUID) { |
288 | setuid(noise_uid); |
289 | seteuid(noise_uid); |
290 | } |
291 | |
292 | /* --- Start the process up --- */ |
293 | |
294 | execle("/bin/sh", "-c", c, (char *)0, env); |
295 | _exit(127); |
296 | } |
297 | |
298 | /* --- Sort out my end of the deal --- */ |
299 | |
300 | close(fd[1]); |
301 | |
302 | /* --- Decide on the deadline --- */ |
303 | |
304 | TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE); |
305 | |
306 | /* --- Now read, and think --- */ |
307 | |
308 | for (;;) { |
309 | struct timeval now, diff; |
310 | fd_set rd; |
311 | |
312 | gettimeofday(&now, 0); |
313 | timer(r, &now); |
314 | if (TV_CMP(&now, >, &dead)) |
315 | break; |
316 | TV_SUB(&diff, &dead, &now); |
317 | |
318 | FD_ZERO(&rd); |
319 | FD_SET(fd[0], &rd); |
320 | |
321 | if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0) |
322 | break; |
323 | if (FD_ISSET(fd[0], &rd)) { |
324 | ssize_t sz; |
325 | int goodbits; |
326 | |
327 | if ((sz = read(fd[0], buf, sizeof(buf))) <= 0) |
328 | break; |
329 | goodbits = (sz * good) / 128; |
330 | rand_add(r, buf, sz, goodbits); |
331 | ret = 1; |
332 | } |
333 | } |
334 | |
335 | /* --- We've finished with it: kill the child process --- * |
336 | * |
337 | * This is morally questionable. On the other hand, I don't want to be |
338 | * held up in the @waitpid@ call if I can possibly help it. Maybe a |
339 | * double-fork is worth doing here. |
340 | */ |
341 | |
342 | close(fd[0]); |
343 | BURN(buf); |
344 | noise_timer(r); |
345 | kill(kid, SIGKILL); |
346 | waitpid(kid, 0, 0); |
347 | return (ret); |
348 | } |
349 | |
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350 | /* --- @noise_freewheel@ --- * |
351 | * |
352 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
353 | * |
354 | * Returns: Nonzero if some randomness was contributed. |
355 | * |
356 | * Use: Runs a free counter for a short while as a desparate attempt |
357 | * to get randomness from somewhere. This is actually quite |
358 | * effective. |
359 | */ |
360 | |
361 | #ifdef USE_FREEWHEEL |
362 | |
363 | static jmp_buf fwjmp; |
364 | |
365 | static void fwalarm(int sig) |
366 | { |
367 | siglongjmp(fwjmp, 1); |
368 | } |
369 | |
370 | int noise_freewheel(rand_pool *r) |
371 | { |
372 | void (*sigal)(int) = 0; |
373 | struct itimerval oitv, itv = { { 0, 0 }, { 0, 5000 } }; |
374 | int rc = 0; |
375 | volatile uint32 fwcount = 0; |
376 | |
377 | if (!sigsetjmp(fwjmp, 1)) { |
378 | if ((sigal = signal(SIGALRM, fwalarm)) == SIG_ERR) |
379 | return (0); |
380 | if (setitimer(ITIMER_REAL, &itv, &oitv)) |
381 | goto done; |
382 | for (;;) |
383 | fwcount++; |
384 | } else { |
385 | octet buf[4]; |
386 | STORE32(buf, fwcount); |
387 | rand_add(r, buf, sizeof(buf), 16); |
388 | rc = 1; |
389 | } |
390 | |
391 | done: |
392 | signal(SIGALRM, sigal); |
393 | TV_SUB(&oitv.it_value, &oitv.it_value, &itv.it_value); |
394 | setitimer(ITIMER_REAL, &oitv, 0); |
395 | return (rc); |
396 | } |
397 | |
398 | #else |
399 | |
400 | int noise_freewheel(rand_pool *r) |
401 | { |
402 | return (0); |
403 | } |
404 | |
405 | #endif |
406 | |
407 | /* --- @noise_enquire@ --- * |
408 | * |
409 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
410 | * |
411 | * Returns: Nonzero if some randomness was contributed. |
412 | * |
413 | * Use: Runs some shell commands to enquire about the prevailing |
414 | * environment. This can gather quite a lot of low-quality |
415 | * entropy. |
416 | */ |
417 | |
418 | int noise_enquire(rand_pool *r) |
419 | { |
420 | struct tab { |
421 | const char *cmd; |
422 | unsigned rate; |
423 | } tab[] = { |
424 | { "ps alxww || ps -elf", 16 }, |
425 | { "netstat -n", 6 }, |
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426 | { "ifconfig -a", 8 }, |
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427 | { "df", 20 }, |
428 | { "w", 6 }, |
429 | { "ls -align /tmp/.", 10 }, |
430 | { 0, 0 } |
431 | }; |
432 | int i; |
433 | |
434 | for (i = 0; tab[i].cmd; i++) |
435 | noise_filter(r, tab[i].rate, tab[i].cmd); |
436 | return (1); |
437 | } |
438 | |
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439 | /* --- @noise_acquire@ --- * |
440 | * |
441 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
442 | * |
443 | * Returns: --- |
444 | * |
445 | * Use: Acquires some randomness from somewhere. |
446 | */ |
447 | |
448 | void noise_acquire(rand_pool *r) |
449 | { |
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450 | unsigned i; |
451 | for (i = 0; i < 8; i++) |
452 | noise_freewheel(r); |
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453 | if (!noise_devrandom(r)) { |
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454 | noise_enquire(r); |
455 | for (i = 0; i < 8; i++) |
456 | noise_freewheel(r); |
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457 | } |
458 | } |
459 | |
460 | /*----- That's all, folks -------------------------------------------------*/ |