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