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1 | /* -*-c-*- |
2 | * |
c141f4b6 |
3 | * $Id: noise.c,v 1.4 1999/12/10 23:25:15 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 $ |
c141f4b6 |
33 | * Revision 1.4 1999/12/10 23:25:15 mdw |
34 | * Bug fix: remove old spurious fflush. |
35 | * |
028b34c6 |
36 | * Revision 1.3 1999/12/10 23:24:11 mdw |
37 | * Bug fix: flush buffers before forking. |
38 | * |
178220b3 |
39 | * Revision 1.2 1999/11/11 00:59:08 mdw |
40 | * A bit of reformatting. Initialize the uid and gid correctly. |
41 | * |
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42 | * Revision 1.1 1999/09/03 08:41:12 mdw |
43 | * Initial import. |
44 | * |
45 | */ |
46 | |
47 | /*----- Header files ------------------------------------------------------*/ |
48 | |
178220b3 |
49 | #include "config.h" |
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50 | |
51 | #include <stdio.h> |
52 | #include <string.h> |
53 | #include <signal.h> |
54 | |
55 | #include <sys/types.h> |
56 | #include <sys/time.h> |
57 | #include <sys/wait.h> |
58 | |
59 | #include <fcntl.h> |
60 | #include <unistd.h> |
61 | |
62 | #ifdef HAVE_SETGROUPS |
63 | # include <grp.h> |
64 | #endif |
65 | |
66 | #include <mLib/bits.h> |
67 | #include <mLib/tv.h> |
68 | |
69 | #include "noise.h" |
70 | #include "paranoia.h" |
71 | #include "rand.h" |
72 | |
73 | /*----- Magical numbers ---------------------------------------------------*/ |
74 | |
75 | #define NOISE_KIDLIFE 100000 /* @noise_filter@ child lifetime */ |
76 | #define MILLION 1000000 /* One million */ |
77 | |
78 | /*----- Noise source definition -------------------------------------------*/ |
79 | |
80 | rand_source noise_source = { noise_acquire, noise_timer }; |
81 | |
82 | /*----- Static variables --------------------------------------------------*/ |
83 | |
84 | /* --- Timer differences --- */ |
85 | |
86 | static unsigned long noise_last; /* Last time recorded */ |
87 | static unsigned long noise_diff; /* Last first order difference */ |
88 | |
89 | /* --- Setuid program handling --- */ |
90 | |
178220b3 |
91 | static uid_t noise_uid = NOISE_NOSETUID; /* Uid to set to spawn processes */ |
92 | static gid_t noise_gid = NOISE_NOSETGID; /* Gid to set to spawn processes */ |
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93 | |
94 | /*----- Main code ---------------------------------------------------------*/ |
95 | |
96 | /* --- @bitcount@ --- * |
97 | * |
98 | * Arguments: @unsigned long x@ = a word containing bits |
99 | * |
100 | * Returns: The number of bits set in the word. |
101 | */ |
102 | |
103 | static int bitcount(unsigned long x) |
104 | { |
105 | char ctab[] = { 0, 1, 1, 2, 1, 2, 2, 3, |
106 | 1, 2, 2, 3, 2, 3, 3, 4 }; |
107 | int count = 0; |
108 | while (x) { |
109 | count += ctab[x & 0xfu]; |
110 | x >>= 4; |
111 | } |
112 | return (count); |
113 | } |
114 | |
115 | /* --- @timer@ --- * |
116 | * |
117 | * Arguments: @rand_pool *r@ = pointer to randomness pool |
118 | * @struct timeval *tv@ = pointer to time block |
119 | * |
120 | * Returns: Nonzer if some randomness was contributed. |
121 | * |
122 | * Use: Low-level timer contributor. |
123 | */ |
124 | |
125 | static int timer(rand_pool *r, struct timeval *tv) |
126 | { |
127 | unsigned long x, d, dd; |
128 | int de, dde; |
129 | int ret; |
130 | |
131 | x = tv->tv_usec + MILLION * tv->tv_sec; |
132 | d = x ^ noise_last; |
133 | dd = d ^ noise_diff; |
134 | noise_diff = d; |
135 | de = bitcount(d); |
136 | dde = bitcount(dd); |
137 | rand_add(r, tv, sizeof(*tv), de <= dde ? de : dde); |
138 | ret = (de || dde); |
139 | BURN(tv); x = d = dd = de = dde = 0; |
140 | return (ret); |
141 | } |
142 | |
143 | /* --- @noise_timer@ --- * |
144 | * |
145 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
146 | * |
147 | * Returns: Nonzero if some randomness was contributed. |
148 | * |
149 | * Use: Contributes the current time to the randomness pool. |
150 | * A guess at the number of useful bits contributed is made, |
151 | * based on first and second order bit differences. This isn't |
152 | * ever-so reliable, but it's better than nothing. |
153 | */ |
154 | |
155 | int noise_timer(rand_pool *r) |
156 | { |
157 | struct timeval tv; |
158 | gettimeofday(&tv, 0); |
159 | return (timer(r, &tv)); |
160 | } |
161 | |
162 | /* --- @noise_devrandom@ --- * |
163 | * |
164 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
165 | * |
166 | * Returns: Nonzero if some randomness was contributed. |
167 | * |
168 | * Use: Attempts to obtain some randomness from the system entropy |
169 | * pool. All bits from the device are assumed to be good. |
170 | */ |
171 | |
172 | int noise_devrandom(rand_pool *r) |
173 | { |
174 | int fd; |
175 | octet buf[RAND_POOLSZ]; |
176 | ssize_t len; |
177 | int ret = 0; |
178 | |
179 | /* --- Be nice to other clients of the random device --- * |
180 | * |
181 | * Attempt to open the device nonblockingly. If that works, take up to |
182 | * one bufferful and then close again. If there's no data to be read, |
183 | * then that's tough and we go away again, on the grounds that the device |
184 | * needs to get some more entropy from somewhere. |
185 | */ |
186 | |
187 | if ((fd = open("/dev/random", O_RDONLY | O_NONBLOCK)) >= 0) { |
188 | if ((len = read(fd, buf, sizeof(buf))) > 0) { |
189 | rand_add(r, buf, len, len * 8); |
190 | BURN(buf); |
191 | ret = 1; |
192 | } |
193 | close(fd); |
194 | } |
195 | noise_timer(r); |
196 | return (ret); |
197 | } |
198 | |
199 | /* --- @noise_setid@ --- * |
200 | * |
201 | * Arguments: @uid_t uid@ = uid to set |
202 | * @gid_t gid@ = gid to set |
203 | * |
204 | * Returns: --- |
205 | * |
206 | * Use: Sets the user and group ids to be used by @noise_filter@ |
207 | * when running child processes. This is useful to avoid |
208 | * giving shell commands (even carefully written ones) undue |
209 | * privileges. |
210 | */ |
211 | |
212 | void noise_setid(uid_t uid, gid_t gid) |
213 | { |
214 | noise_uid = uid; |
215 | noise_gid = gid; |
216 | } |
217 | |
218 | /* --- @noise_filter@ --- * |
219 | * |
220 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
221 | * @int good@ = number of good bits per 1024 bits |
222 | * @const char *c@ = shell command to run |
223 | * |
224 | * Returns: Nonzero if some randomness was contributed. |
225 | * |
226 | * Use: Attempts to execute a shell command, and dump it into the |
227 | * randomness pool. A very rough estimate of the number of |
228 | * good bits is made, based on the size of the command's output. |
229 | * This function calls @waitpid@, so be careful. Before execing |
230 | * the command, the process uid and gid are set to the values |
231 | * given to @noise_setid@, and an attempt is made to reset the |
232 | * list of supplementary groups. The environment passed to |
233 | * the command has been severly lobotimized. If the command |
234 | * fails to complete within a short time period, it is killed. |
235 | * Paranoid use of close-on-exec flags for file descriptors is |
236 | * recommended. |
237 | */ |
238 | |
239 | int noise_filter(rand_pool *r, int good, const char *c) |
240 | { |
241 | char buf[4096]; |
242 | pid_t kid; |
243 | int fd[2]; |
244 | struct timeval dead; |
245 | int ret = 0; |
246 | const char *env[] = { |
247 | "PATH=/bin:/usr/bin:/sbin:/usr/sbin:/etc", |
248 | 0 |
249 | }; |
250 | |
251 | /* --- Remember when this business started --- */ |
252 | |
253 | gettimeofday(&dead, 0); |
254 | timer(r, &dead); |
255 | |
256 | /* --- Create a pipe --- */ |
257 | |
258 | if (pipe(fd)) |
259 | return (ret); |
260 | |
261 | /* --- Fork a child off --- */ |
262 | |
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263 | fflush(0); |
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264 | kid = fork(); |
265 | if (kid < 0) { |
266 | close(fd[0]); |
267 | close(fd[1]); |
268 | return (ret); |
269 | } |
270 | |
271 | /* --- Handle the child end of the deal --- */ |
272 | |
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273 | if (kid == 0) { |
274 | int f; |
275 | |
276 | /* --- Set the pipe as standard output, close standard input --- */ |
277 | |
278 | close(0); close(1); close(2); |
279 | |
280 | if (fd[1] != 1) { |
281 | if (dup2(fd[1], 1) < 0) _exit(127); |
282 | close(fd[1]); |
283 | } |
284 | |
285 | if ((f = open("/dev/null", O_RDONLY)) != 0 || |
286 | (f = open("/dev/null", O_WRONLY)) != 2) |
287 | _exit(127); |
288 | |
289 | /* --- Play games with uids --- */ |
290 | |
291 | if (noise_gid != NOISE_NOSETGID) { |
292 | setgid(noise_gid); |
293 | setegid(noise_gid); |
294 | #ifdef HAVE_SETGROUPS |
295 | setgroups(1, &noise_gid); |
296 | #endif |
297 | } |
298 | |
299 | if (noise_uid != NOISE_NOSETUID) { |
300 | setuid(noise_uid); |
301 | seteuid(noise_uid); |
302 | } |
303 | |
304 | /* --- Start the process up --- */ |
305 | |
306 | execle("/bin/sh", "-c", c, (char *)0, env); |
307 | _exit(127); |
308 | } |
309 | |
310 | /* --- Sort out my end of the deal --- */ |
311 | |
312 | close(fd[1]); |
313 | |
314 | /* --- Decide on the deadline --- */ |
315 | |
316 | TV_ADDL(&dead, &dead, 0, NOISE_KIDLIFE); |
317 | |
318 | /* --- Now read, and think --- */ |
319 | |
320 | for (;;) { |
321 | struct timeval now, diff; |
322 | fd_set rd; |
323 | |
324 | gettimeofday(&now, 0); |
325 | timer(r, &now); |
326 | if (TV_CMP(&now, >, &dead)) |
327 | break; |
328 | TV_SUB(&diff, &dead, &now); |
329 | |
330 | FD_ZERO(&rd); |
331 | FD_SET(fd[0], &rd); |
332 | |
333 | if (select(fd[0] + 1, &rd, 0, 0, &diff) < 0) |
334 | break; |
335 | if (FD_ISSET(fd[0], &rd)) { |
336 | ssize_t sz; |
337 | int goodbits; |
338 | |
339 | if ((sz = read(fd[0], buf, sizeof(buf))) <= 0) |
340 | break; |
341 | goodbits = (sz * good) / 128; |
342 | rand_add(r, buf, sz, goodbits); |
343 | ret = 1; |
344 | } |
345 | } |
346 | |
347 | /* --- We've finished with it: kill the child process --- * |
348 | * |
349 | * This is morally questionable. On the other hand, I don't want to be |
350 | * held up in the @waitpid@ call if I can possibly help it. Maybe a |
351 | * double-fork is worth doing here. |
352 | */ |
353 | |
354 | close(fd[0]); |
355 | BURN(buf); |
356 | noise_timer(r); |
357 | kill(kid, SIGKILL); |
358 | waitpid(kid, 0, 0); |
359 | return (ret); |
360 | } |
361 | |
362 | /* --- @noise_acquire@ --- * |
363 | * |
364 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
365 | * |
366 | * Returns: --- |
367 | * |
368 | * Use: Acquires some randomness from somewhere. |
369 | */ |
370 | |
371 | void noise_acquire(rand_pool *r) |
372 | { |
373 | if (!noise_devrandom(r)) { |
374 | |
375 | /* --- Output of `ps' --- * |
376 | * |
377 | * This is a hopefully cheap way of getting a bit of noise. I'm guessing |
378 | * the good bit ratio based on about 90 bytes per line of output, and |
379 | * each line containing maybe 12 bits worth of interesting data. (Some |
380 | * quick experiments with gzip seem to bear this idea out.) So, 12 good |
381 | * bits per 90 bytes of output gives slightly more than 17 good bits per |
382 | * 1024 bits of output. So I'll be a pessimist and say 16 bits. |
383 | */ |
384 | |
385 | (void) |
386 | (noise_filter(r, 16, "ps alxww") || |
387 | noise_filter(r, 16, "ps -elf")); |
388 | |
389 | /* --- Output of `netstat' --- * |
390 | * |
391 | * Another possibly cheap way of getting noise. My output has about |
392 | * 72 bytes per line of output. My wild guesses are telling me that |
393 | * there are probably only about four good bits per line (gzip tells |
394 | * me there's six, but I want to underestimate). Four bits per 72 bytes |
395 | * is 7 good bits per 1024 bits of output. Pessimist that I am, I'll |
396 | * call it six. |
397 | */ |
398 | |
399 | noise_filter(r, 6, "netstat -n"); |
400 | } |
401 | } |
402 | |
403 | /*----- That's all, folks -------------------------------------------------*/ |