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*/
1 /*
2 * random.c -- A strong random number generator
3 *
4 * Version 0.95, last modified 4-Nov-95
5 *
6 * Copyright Theodore Ts'o, 1994, 1995. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, and the entire permission notice in its entirety,
13 * including the disclaimer of warranties.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. The name of the author may not be used to endorse or promote
18 * products derived from this software without specific prior
19 * written permission.
20 *
21 * ALTERNATIVELY, this product may be distributed under the terms of
22 * the GNU Public License, in which case the provisions of the GPL are
23 * required INSTEAD OF the above restrictions. (This clause is
24 * necessary due to a potential bad interaction between the GPL and
25 * the restrictions contained in a BSD-style copyright.)
26 *
27 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
28 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
30 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
31 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
32 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
33 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
35 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
36 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
37 * OF THE POSSIBILITY OF SUCH DAMAGE.
38 */
39
40 /*
41 * (now, with legal B.S. out of the way.....)
42 *
43 * This routine gathers environmental noise from device drivers, etc.,
44 * and returns good random numbers, suitable for cryptographic use.
45 * Besides the obvious cryptographic uses, these numbers are also good
46 * for seeding TCP sequence numbers, and other places where it is
47 * desireable to have numbers which are not only random, but hard to
48 * predict by an attacker.
49 *
50 * Theory of operation
51 * ===================
52 *
53 * Computers are very predictable devices. Hence it is extremely hard
54 * to produce truely random numbers on a computer --- as opposed to
55 * pseudo-random numbers, which can easily generated by using a
56 * algorithm. Unfortunately, it is very easy for attackers to guess
57 * the sequence of pseudo-random number generators, and for some
58 * applications this is not acceptable. So instead, we must try to
59 * gather "environmental noise" from the computer's environment, which
60 * must be hard for outside attackers to observe, and use that to
61 * generate random numbers. In a Unix environment, this is best done
62 * from inside the kernel.
63 *
64 * Sources of randomness from the environment include inter-keyboard
65 * timings, inter-interrupt timings from some interrupts, and other
66 * events which are both (a) non-deterministic and (b) hard for an
67 * outside observer to measure. Randomness from these sources are
68 * added to an "entropy pool", which is mixed using a CRC-like function.
69 * This is not cryptographically strong, but it is adequate assuming
70 * the randomness is not chosen maliciously, and it is fast enough that
71 * the overhead of doing it on every interrupt is very reasonable.
72 * As random bytes are mixed into the entropy pool, the routines keep
73 * an *estimate* of how many bits of randomness have been stored into
74 * the random number generator's internal state.
75 *
76 * When random bytes are desired, they are obtained by taking the MD5
77 * hash of the contents of the "entropy pool". The MD5 hash avoids
78 * exposing the internal state of the entropy pool. It is believed to
79 * be computationally infeasible to derive any useful information
80 * about the input of MD5 from its output. Even if it is possible to
81 * analyze MD5 in some clever way, as long as the amount of data
82 * returned from the generator is less than the inherent entropy in
83 * the pool, the output data is totally unpredictable. For this
84 * reason, the routine decreases its internal estimate of how many
85 * bits of "true randomness" are contained in the entropy pool as it
86 * outputs random numbers.
87 *
88 * If this estimate goes to zero, the routine can still generate
89 * random numbers; however, an attacker may (at least in theory) be
90 * able to infer the future output of the generator from prior
91 * outputs. This requires successful cryptanalysis of MD5, which is
92 * not believed to be feasible, but there is a remote possiblility.
93 * Nonetheless, these numbers should be useful for the vast majority
94 * of purposes.
95 *
96 * Exported interfaces ---- output
97 * ===============================
98 *
99 * There are three exported interfaces; the first is one designed to
100 * be used from within the kernel:
101 *
102 * void get_random_bytes(void *buf, int nbytes);
103 *
104 * This interface will return the requested number of random bytes,
105 * and place it in the requested buffer.
106 *
107 * The two other interfaces are two character devices /dev/random and
108 * /dev/urandom. /dev/random is suitable for use when very high
109 * quality randomness is desired (for example, for key generation or
110 * one-time pads), as it will only return a maximum of the number of
111 * bits of randomness (as estimated by the random number generator)
112 * contained in the entropy pool.
113 *
114 * The /dev/urandom device does not have this limit, and will return
115 * as many bytes as are requested. As more and more random bytes are
116 * requested without giving time for the entropy pool to recharge,
117 * this will result in random numbers that are merely cryptographically
118 * strong. For many applications, however, this is acceptable.
119 *
120 * Exported interfaces ---- input
121 * ==============================
122 *
123 * The current exported interfaces for gathering environmental noise
124 * from the devices are:
125 *
126 * void add_keyboard_randomness(unsigned char scancode);
127 * void add_mouse_randomness(__u32 mouse_data);
128 * void add_interrupt_randomness(int irq);
129 * void add_blkdev_randomness(int irq);
130 *
131 * add_keyboard_randomness() uses the inter-keypress timing, as well as the
132 * scancode as random inputs into the "entropy pool".
133 *
134 * add_mouse_randomness() uses the mouse interrupt timing, as well as
135 * the reported position of the mouse from the hardware.
136 *
137 * add_interrupt_randomness() uses the inter-interrupt timing as random
138 * inputs to the entropy pool. Note that not all interrupts are good
139 * sources of randomness! For example, the timer interrupts is not a
140 * good choice, because the periodicity of the interrupts is to
141 * regular, and hence predictable to an attacker. Disk interrupts are
142 * a better measure, since the timing of the disk interrupts are more
143 * unpredictable.
144 *
145 * add_blkdev_randomness() times the finishing time of block requests.
146 *
147 * All of these routines try to estimate how many bits of randomness a
148 * particular randomness source. They do this by keeping track of the
149 * first and second order deltas of the event timings.
150 *
151 * Acknowledgements:
152 * =================
153 *
154 * Ideas for constructing this random number generator were derived
155 * from the Pretty Good Privacy's random number generator, and from
156 * private discussions with Phil Karn. Colin Plumb provided a faster
157 * random number generator, which speed up the mixing function of the
158 * entropy pool, taken from PGP 3.0 (under development). It has since
159 * been modified by myself to provide better mixing in the case where
160 * the input values to add_entropy_word() are mostly small numbers.
161 *
162 * Any flaws in the design are solely my responsibility, and should
163 * not be attributed to the Phil, Colin, or any of authors of PGP.
164 *
165 * The code for MD5 transform was taken from Colin Plumb's
166 * implementation, which has been placed in the public domain. The
167 * MD5 cryptographic checksum was devised by Ronald Rivest, and is
168 * documented in RFC 1321, "The MD5 Message Digest Algorithm".
169 *
170 * Further background information on this topic may be obtained from
171 * RFC 1750, "Randomness Recommendations for Security", by Donald
172 * Eastlake, Steve Crocker, and Jeff Schiller.
173 */
174
175 #include <linux/sched.h>
176 #include <linux/kernel.h>
177 #include <linux/major.h>
178 #include <linux/string.h>
179 #include <linux/fcntl.h>
180 #include <linux/malloc.h>
181 #include <linux/random.h>
182
183 #include <asm/segment.h>
184 #include <asm/irq.h>
185 #include <asm/io.h>
186
187 /*
188 * The pool is stirred with a primitive polynomial of degree 128
189 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
190 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
191 */
192 #define POOLWORDS 128 /* Power of 2 - note that this is 32-bit words */
193 #define POOLBITS (POOLWORDS*32)
194 #if POOLWORDS == 128
195 #define TAP1 99 /* The polynomial taps */
196 #define TAP2 59
197 #define TAP3 31
198 #define TAP4 9
199 #define TAP5 7
200 #elif POOLWORDS == 64
201 #define TAP1 62 /* The polynomial taps */
202 #define TAP2 38
203 #define TAP3 10
204 #define TAP4 6
205 #define TAP5 1
206 #else
207 #error No primitive polynomial available for chosen POOLWORDS
208 #endif
209
210 /* There is actually only one of these, globally. */
211 struct random_bucket {
212 unsigned add_ptr;
213 unsigned entropy_count;
214 int input_rotate;
215 __u32 *pool;
216 };
217
218 /* There is one of these per entropy source */
219 struct timer_rand_state {
220 unsigned long last_time;
221 int last_delta;
222 int dont_count_entropy:1;
223 };
224
225 static struct random_bucket random_state;
226 static __u32 random_pool[POOLWORDS];
227 static struct timer_rand_state keyboard_timer_state;
228 static struct timer_rand_state mouse_timer_state;
229 static struct timer_rand_state extract_timer_state;
230 static struct timer_rand_state *irq_timer_state[NR_IRQS];
231 static struct timer_rand_state *blkdev_timer_state[MAX_BLKDEV];
232 static struct wait_queue *random_wait;
233
234 static int random_read(struct inode * inode, struct file * file,
235 char * buf, int nbytes);
236 static int random_read_unlimited(struct inode * inode, struct file * file,
237 char * buf, int nbytes);
238 static int random_select(struct inode *inode, struct file *file,
239 int sel_type, select_table * wait);
240 static int random_write(struct inode * inode, struct file * file,
241 const char * buffer, int count);
242 static int random_ioctl(struct inode * inode, struct file * file,
243 unsigned int cmd, unsigned long arg);
244
245
246 #ifndef MIN
247 #define MIN(a,b) (((a) < (b)) ? (a) : (b))
248 #endif
249
250 void rand_initialize(void)
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*/
251 {
252 random_state.add_ptr = 0;
253 random_state.entropy_count = 0;
254 random_state.pool = random_pool;
255 memset(irq_timer_state, 0, sizeof(irq_timer_state));
256 memset(blkdev_timer_state, 0, sizeof(blkdev_timer_state));
257 extract_timer_state.dont_count_entropy = 1;
258 random_wait = NULL;
259 }
260
261 void rand_initialize_irq(int irq)
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*/
262 {
263 struct timer_rand_state *state;
264
265 if (irq >= NR_IRQS || irq_timer_state[irq])
266 return;
267
268 /*
269 * If kamlloc returns null, we just won't use that entropy
270 * source.
271 */
272 state = kmalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
273 if (state) {
274 irq_timer_state[irq] = state;
275 memset(state, 0, sizeof(struct timer_rand_state));
276 }
277 }
278
279 void rand_initialize_blkdev(int major)
/* */
280 {
281 struct timer_rand_state *state;
282
283 if (major >= MAX_BLKDEV || blkdev_timer_state[major])
284 return;
285
286 /*
287 * If kamlloc returns null, we just won't use that entropy
288 * source.
289 */
290 state = kmalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
291 if (state) {
292 blkdev_timer_state[major] = state;
293 memset(state, 0, sizeof(struct timer_rand_state));
294 }
295 }
296
297 /*
298 * This function adds a byte into the entropy "pool". It does not
299 * update the entropy estimate. The caller must do this if appropriate.
300 *
301 * The pool is stirred with a primitive polynomial of degree 128
302 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
303 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
304 *
305 * We rotate the input word by a changing number of bits, to help
306 * assure that all bits in the entropy get toggled. Otherwise, if we
307 * consistently feed the entropy pool small numbers (like jiffies and
308 * scancodes, for example), the upper bits of the entropy pool don't
309 * get affected. --- TYT, 10/11/95
310 */
311 static inline void add_entropy_word(struct random_bucket *r,
/* */
312 const __u32 input)
313 {
314 unsigned i;
315 __u32 w;
316
317 w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
318 i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
319 if (i)
320 r->input_rotate = (r->input_rotate + 7) & 31;
321 else
322 /*
323 * At the beginning of the pool, add an extra 7 bits
324 * rotation, so that successive passes spread the
325 * input bits across the pool evenly.
326 */
327 r->input_rotate = (r->input_rotate + 14) & 31;
328
329 /* XOR in the various taps */
330 w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
331 w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
332 w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
333 w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
334 w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
335 w ^= r->pool[i];
336 /* Rotate w left 1 bit (stolen from SHA) and store */
337 r->pool[i] = (w << 1) | (w >> 31);
338 }
339
340 /*
341 * This function adds entropy to the entropy "pool" by using timing
342 * delays. It uses the timer_rand_state structure to make an estimate
343 * of how many bits of entropy this call has added to the pool.
344 *
345 * The number "num" is also added to the pool - it should somehow describe
346 * the type of event which just happened. This is currently 0-255 for
347 * keyboard scan codes, and 256 upwards for interrupts.
348 * On the i386, this is assumed to be at most 16 bits, and the high bits
349 * are used for a high-resolution timer.
350 *
351 * TODO: Read the time stamp register on the Pentium.
352 */
353 static void add_timer_randomness(struct random_bucket *r,
/* */
354 struct timer_rand_state *state, unsigned num)
355 {
356 int delta, delta2;
357 unsigned nbits;
358 __u32 time;
359
360 #if defined (__i386__)
361 if (x86_capability & 16) {
362 unsigned long low, high;
363 __asm__(".byte 0x0f,0x31"
364 :"=a" (low), "=d" (high));
365 time = (__u32) low;
366 num ^= (__u32) high;
367 } else {
368 #if 0
369 /*
370 * On a 386, read the high resolution timer. We assume that
371 * this gives us 2 bits of randomness.
372 *
373 * This is turned off for now because of the speed hit
374 * it entails.
375 */
376 outb_p(0x00, 0x43); /* latch the count ASAP */
377 num |= inb_p(0x40) << 16;
378 num |= inb(0x40) << 24;
379 if (!state->dont_count_entropy)
380 r->entropy_count += 2;
381 #endif
382
383 time = jiffies;
384 }
385 #else
386 time = jiffies;
387 #endif
388
389 add_entropy_word(r, (__u32) num);
390 add_entropy_word(r, time);
391
392 /*
393 * Calculate number of bits of randomness we probably
394 * added. We take into account the first and second order
395 * deltas in order to make our estimate.
396 */
397 if (!state->dont_count_entropy) {
398 delta = time - state->last_time;
399 state->last_time = time;
400
401 delta2 = delta - state->last_delta;
402 state->last_delta = delta;
403
404 if (delta < 0) delta = -delta;
405 if (delta2 < 0) delta2 = -delta2;
406 delta = MIN(delta, delta2) >> 1;
407 for (nbits = 0; delta; nbits++)
408 delta >>= 1;
409
410 r->entropy_count += nbits;
411
412 /* Prevent overflow */
413 if (r->entropy_count > POOLBITS)
414 r->entropy_count = POOLBITS;
415 }
416
417 wake_up_interruptible(&random_wait);
418 }
419
420 void add_keyboard_randomness(unsigned char scancode)
/* */
421 {
422 add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
423 }
424
425 void add_mouse_randomness(__u32 mouse_data)
/* */
426 {
427 add_timer_randomness(&random_state, &mouse_timer_state, mouse_data);
428 }
429
430 void add_interrupt_randomness(int irq)
/* */
431 {
432 if (irq >= NR_IRQS || irq_timer_state[irq] == 0)
433 return;
434
435 add_timer_randomness(&random_state, irq_timer_state[irq], 0x100+irq);
436 }
437
438 void add_blkdev_randomness(int major)
/* */
439 {
440 if (major >= MAX_BLKDEV || blkdev_timer_state[major] == 0)
441 return;
442
443 add_timer_randomness(&random_state, blkdev_timer_state[major],
444 0x200+major);
445 }
446
447 /*
448 * MD5 transform algorithm, taken from code written by Colin Plumb,
449 * and put into the public domain
450 *
451 * QUESTION: Replace this with SHA, which as generally received better
452 * reviews from the cryptographic community?
453 */
454
455 /* The four core functions - F1 is optimized somewhat */
456
457 /* #define F1(x, y, z) (x & y | ~x & z) */
458 #define F1(x, y, z) (z ^ (x & (y ^ z)))
459 #define F2(x, y, z) F1(z, x, y)
460 #define F3(x, y, z) (x ^ y ^ z)
461 #define F4(x, y, z) (y ^ (x | ~z))
462
463 /* This is the central step in the MD5 algorithm. */
464 #define MD5STEP(f, w, x, y, z, data, s) \
465 ( w += f(x, y, z) + data, w = w<<s | w>>(32-s), w += x )
466
467 /*
468 * The core of the MD5 algorithm, this alters an existing MD5 hash to
469 * reflect the addition of 16 longwords of new data. MD5Update blocks
470 * the data and converts bytes into longwords for this routine.
471 */
472 static void MD5Transform(__u32 buf[4],
/* */
473 __u32 const in[16])
474 {
475 __u32 a, b, c, d;
476
477 a = buf[0];
478 b = buf[1];
479 c = buf[2];
480 d = buf[3];
481
482 MD5STEP(F1, a, b, c, d, in[ 0]+0xd76aa478, 7);
483 MD5STEP(F1, d, a, b, c, in[ 1]+0xe8c7b756, 12);
484 MD5STEP(F1, c, d, a, b, in[ 2]+0x242070db, 17);
485 MD5STEP(F1, b, c, d, a, in[ 3]+0xc1bdceee, 22);
486 MD5STEP(F1, a, b, c, d, in[ 4]+0xf57c0faf, 7);
487 MD5STEP(F1, d, a, b, c, in[ 5]+0x4787c62a, 12);
488 MD5STEP(F1, c, d, a, b, in[ 6]+0xa8304613, 17);
489 MD5STEP(F1, b, c, d, a, in[ 7]+0xfd469501, 22);
490 MD5STEP(F1, a, b, c, d, in[ 8]+0x698098d8, 7);
491 MD5STEP(F1, d, a, b, c, in[ 9]+0x8b44f7af, 12);
492 MD5STEP(F1, c, d, a, b, in[10]+0xffff5bb1, 17);
493 MD5STEP(F1, b, c, d, a, in[11]+0x895cd7be, 22);
494 MD5STEP(F1, a, b, c, d, in[12]+0x6b901122, 7);
495 MD5STEP(F1, d, a, b, c, in[13]+0xfd987193, 12);
496 MD5STEP(F1, c, d, a, b, in[14]+0xa679438e, 17);
497 MD5STEP(F1, b, c, d, a, in[15]+0x49b40821, 22);
498
499 MD5STEP(F2, a, b, c, d, in[ 1]+0xf61e2562, 5);
500 MD5STEP(F2, d, a, b, c, in[ 6]+0xc040b340, 9);
501 MD5STEP(F2, c, d, a, b, in[11]+0x265e5a51, 14);
502 MD5STEP(F2, b, c, d, a, in[ 0]+0xe9b6c7aa, 20);
503 MD5STEP(F2, a, b, c, d, in[ 5]+0xd62f105d, 5);
504 MD5STEP(F2, d, a, b, c, in[10]+0x02441453, 9);
505 MD5STEP(F2, c, d, a, b, in[15]+0xd8a1e681, 14);
506 MD5STEP(F2, b, c, d, a, in[ 4]+0xe7d3fbc8, 20);
507 MD5STEP(F2, a, b, c, d, in[ 9]+0x21e1cde6, 5);
508 MD5STEP(F2, d, a, b, c, in[14]+0xc33707d6, 9);
509 MD5STEP(F2, c, d, a, b, in[ 3]+0xf4d50d87, 14);
510 MD5STEP(F2, b, c, d, a, in[ 8]+0x455a14ed, 20);
511 MD5STEP(F2, a, b, c, d, in[13]+0xa9e3e905, 5);
512 MD5STEP(F2, d, a, b, c, in[ 2]+0xfcefa3f8, 9);
513 MD5STEP(F2, c, d, a, b, in[ 7]+0x676f02d9, 14);
514 MD5STEP(F2, b, c, d, a, in[12]+0x8d2a4c8a, 20);
515
516 MD5STEP(F3, a, b, c, d, in[ 5]+0xfffa3942, 4);
517 MD5STEP(F3, d, a, b, c, in[ 8]+0x8771f681, 11);
518 MD5STEP(F3, c, d, a, b, in[11]+0x6d9d6122, 16);
519 MD5STEP(F3, b, c, d, a, in[14]+0xfde5380c, 23);
520 MD5STEP(F3, a, b, c, d, in[ 1]+0xa4beea44, 4);
521 MD5STEP(F3, d, a, b, c, in[ 4]+0x4bdecfa9, 11);
522 MD5STEP(F3, c, d, a, b, in[ 7]+0xf6bb4b60, 16);
523 MD5STEP(F3, b, c, d, a, in[10]+0xbebfbc70, 23);
524 MD5STEP(F3, a, b, c, d, in[13]+0x289b7ec6, 4);
525 MD5STEP(F3, d, a, b, c, in[ 0]+0xeaa127fa, 11);
526 MD5STEP(F3, c, d, a, b, in[ 3]+0xd4ef3085, 16);
527 MD5STEP(F3, b, c, d, a, in[ 6]+0x04881d05, 23);
528 MD5STEP(F3, a, b, c, d, in[ 9]+0xd9d4d039, 4);
529 MD5STEP(F3, d, a, b, c, in[12]+0xe6db99e5, 11);
530 MD5STEP(F3, c, d, a, b, in[15]+0x1fa27cf8, 16);
531 MD5STEP(F3, b, c, d, a, in[ 2]+0xc4ac5665, 23);
532
533 MD5STEP(F4, a, b, c, d, in[ 0]+0xf4292244, 6);
534 MD5STEP(F4, d, a, b, c, in[ 7]+0x432aff97, 10);
535 MD5STEP(F4, c, d, a, b, in[14]+0xab9423a7, 15);
536 MD5STEP(F4, b, c, d, a, in[ 5]+0xfc93a039, 21);
537 MD5STEP(F4, a, b, c, d, in[12]+0x655b59c3, 6);
538 MD5STEP(F4, d, a, b, c, in[ 3]+0x8f0ccc92, 10);
539 MD5STEP(F4, c, d, a, b, in[10]+0xffeff47d, 15);
540 MD5STEP(F4, b, c, d, a, in[ 1]+0x85845dd1, 21);
541 MD5STEP(F4, a, b, c, d, in[ 8]+0x6fa87e4f, 6);
542 MD5STEP(F4, d, a, b, c, in[15]+0xfe2ce6e0, 10);
543 MD5STEP(F4, c, d, a, b, in[ 6]+0xa3014314, 15);
544 MD5STEP(F4, b, c, d, a, in[13]+0x4e0811a1, 21);
545 MD5STEP(F4, a, b, c, d, in[ 4]+0xf7537e82, 6);
546 MD5STEP(F4, d, a, b, c, in[11]+0xbd3af235, 10);
547 MD5STEP(F4, c, d, a, b, in[ 2]+0x2ad7d2bb, 15);
548 MD5STEP(F4, b, c, d, a, in[ 9]+0xeb86d391, 21);
549
550 buf[0] += a;
551 buf[1] += b;
552 buf[2] += c;
553 buf[3] += d;
554 }
555
556 #undef F1
557 #undef F2
558 #undef F3
559 #undef F4
560 #undef MD5STEP
561
562
563 #if POOLWORDS % 16
564 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
565 #endif
566 /*
567 * This function extracts randomness from the "entropy pool", and
568 * returns it in a buffer. This function computes how many remaining
569 * bits of entropy are left in the pool, but it does not restrict the
570 * number of bytes that are actually obtained.
571 */
572 static inline int extract_entropy(struct random_bucket *r, char * buf,
/* */
573 int nbytes, int to_user)
574 {
575 int ret, i;
576 __u32 tmp[4];
577
578 add_timer_randomness(r, &extract_timer_state, nbytes);
579
580 /* Redundant, but just in case... */
581 if (r->entropy_count > POOLBITS)
582 r->entropy_count = POOLBITS;
583 /* Why is this here? Left in from Ted Ts'o. Perhaps to limit time. */
584 if (nbytes > 32768)
585 nbytes = 32768;
586
587 ret = nbytes;
588 if (r->entropy_count / 8 >= nbytes)
589 r->entropy_count -= nbytes*8;
590 else
591 r->entropy_count = 0;
592
593 while (nbytes) {
594 /* Hash the pool to get the output */
595 tmp[0] = 0x67452301;
596 tmp[1] = 0xefcdab89;
597 tmp[2] = 0x98badcfe;
598 tmp[3] = 0x10325476;
599 for (i = 0; i < POOLWORDS; i += 16)
600 MD5Transform(tmp, r->pool+i);
601 /* Modify pool so next hash will produce different results */
602 add_entropy_word(r, tmp[0]);
603 add_entropy_word(r, tmp[1]);
604 add_entropy_word(r, tmp[2]);
605 add_entropy_word(r, tmp[3]);
606 /*
607 * Run the MD5 Transform one more time, since we want
608 * to add at least minimal obscuring of the inputs to
609 * add_entropy_word(). --- TYT
610 */
611 MD5Transform(tmp, r->pool);
612
613 /* Copy data to destination buffer */
614 i = MIN(nbytes, 16);
615 if (to_user)
616 memcpy_tofs(buf, (__u8 const *)tmp, i);
617 else
618 memcpy(buf, (__u8 const *)tmp, i);
619 nbytes -= i;
620 buf += i;
621 }
622
623 /* Wipe data from memory */
624 memset(tmp, 0, sizeof(tmp));
625
626 return ret;
627 }
628
629 /*
630 * This function is the exported kernel interface. It returns some
631 * number of good random numbers, suitable for seeding TCP sequence
632 * numbers, etc.
633 */
634 void get_random_bytes(void *buf, int nbytes)
/* */
635 {
636 extract_entropy(&random_state, (char *) buf, nbytes, 0);
637 }
638
639 static int
640 random_read(struct inode * inode, struct file * file, char * buf, int nbytes)
/* */
641 {
642 struct wait_queue wait = { current, NULL };
643 int n;
644 int retval = 0;
645 int count = 0;
646
647 if (nbytes == 0)
648 return 0;
649
650 add_wait_queue(&random_wait, &wait);
651 while (nbytes > 0) {
652 current->state = TASK_INTERRUPTIBLE;
653
654 n = nbytes;
655 if (n > random_state.entropy_count / 8)
656 n = random_state.entropy_count / 8;
657 if (n == 0) {
658 if (file->f_flags & O_NONBLOCK) {
659 retval = -EAGAIN;
660 break;
661 }
662 if (current->signal & ~current->blocked) {
663 retval = -ERESTARTSYS;
664 break;
665 }
666 schedule();
667 continue;
668 }
669 n = extract_entropy(&random_state, buf, n, 1);
670 count += n;
671 buf += n;
672 nbytes -= n;
673 break; /* This break makes the device work */
674 /* like a named pipe */
675 }
676 current->state = TASK_RUNNING;
677 remove_wait_queue(&random_wait, &wait);
678
679 return (count ? count : retval);
680 }
681
682 static int
683 random_read_unlimited(struct inode * inode, struct file * file,
/* */
684 char * buf, int nbytes)
685 {
686 return extract_entropy(&random_state, buf, nbytes, 1);
687 }
688
689 static int
690 random_select(struct inode *inode, struct file *file,
/* */
691 int sel_type, select_table * wait)
692 {
693 if (sel_type == SEL_IN) {
694 if (random_state.entropy_count >= 8)
695 return 1;
696 select_wait(&random_wait, wait);
697 }
698 return 0;
699 }
700
701 static int
702 random_write(struct inode * inode, struct file * file,
/* */
703 const char * buffer, int count)
704 {
705 int i;
706 __u32 word, *p;
707
708 for (i = count, p = (__u32 *)buffer;
709 i >= sizeof(__u32);
710 i-= sizeof(__u32), p++) {
711 memcpy_fromfs(&word, p, sizeof(__u32));
712 add_entropy_word(&random_state, word);
713 }
714 if (i) {
715 word = 0;
716 memcpy_fromfs(&word, p, i);
717 add_entropy_word(&random_state, word);
718 }
719 if (inode)
720 inode->i_mtime = CURRENT_TIME;
721 return count;
722 }
723
724 static int
725 random_ioctl(struct inode * inode, struct file * file,
/* ![[last]](../icons/n_last.png)
*/
726 unsigned int cmd, unsigned long arg)
727 {
728 int *p, size, ent_count;
729 int retval;
730
731 switch (cmd) {
732 case RNDGETENTCNT:
733 retval = verify_area(VERIFY_WRITE, (void *) arg, sizeof(int));
734 if (retval)
735 return(retval);
736 put_user(random_state.entropy_count, (int *) arg);
737 return 0;
738 case RNDADDTOENTCNT:
739 if (!suser())
740 return -EPERM;
741 retval = verify_area(VERIFY_READ, (void *) arg, sizeof(int));
742 if (retval)
743 return(retval);
744 random_state.entropy_count += get_user((int *) arg);
745 if (random_state.entropy_count > POOLBITS)
746 random_state.entropy_count = POOLBITS;
747 return 0;
748 case RNDGETPOOL:
749 if (!suser())
750 return -EPERM;
751 p = (int *) arg;
752 retval = verify_area(VERIFY_WRITE, (void *) p, sizeof(int));
753 if (retval)
754 return(retval);
755 put_user(random_state.entropy_count, p++);
756 retval = verify_area(VERIFY_READ, (void *) p, sizeof(int));
757 if (retval)
758 return(retval);
759 size = get_user(p);
760 put_user(POOLWORDS, p);
761 if (size < 0)
762 return -EINVAL;
763 if (size > POOLWORDS)
764 size = POOLWORDS;
765 memcpy_tofs(++p, random_state.pool,
766 size*sizeof(__u32));
767 return 0;
768 case RNDADDENTROPY:
769 if (!suser())
770 return -EPERM;
771 p = (int *) arg;
772 retval = verify_area(VERIFY_READ, (void *) p, 2*sizeof(int));
773 if (retval)
774 return(retval);
775 ent_count = get_user(p++);
776 size = get_user(p++);
777 (void) random_write(0, file, (const char *) p, size);
778 random_state.entropy_count += ent_count;
779 if (random_state.entropy_count > POOLBITS)
780 random_state.entropy_count = POOLBITS;
781 return 0;
782 case RNDZAPENTCNT:
783 if (!suser())
784 return -EPERM;
785 random_state.entropy_count = 0;
786 return 0;
787 default:
788 return -EINVAL;
789 }
790 }
791
792 struct file_operations random_fops = {
793 NULL, /* random_lseek */
794 random_read,
795 random_write,
796 NULL, /* random_readdir */
797 random_select, /* random_select */
798 random_ioctl,
799 NULL, /* random_mmap */
800 NULL, /* no special open code */
801 NULL /* no special release code */
802 };
803
804 struct file_operations urandom_fops = {
805 NULL, /* unrandom_lseek */
806 random_read_unlimited,
807 random_write,
808 NULL, /* urandom_readdir */
809 NULL, /* urandom_select */
810 random_ioctl,
811 NULL, /* urandom_mmap */
812 NULL, /* no special open code */
813 NULL /* no special release code */
814 };
815
![[bottom]](../icons/n_bottom.png){kind=icon}
*/