2 * random.c -- A strong random number generator
4 * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
6 * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, and the entire permission notice in its entirety,
14 * including the disclaimer of warranties.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. The name of the author may not be used to endorse or promote
19 * products derived from this software without specific prior
22 * ALTERNATIVELY, this product may be distributed under the terms of
23 * the GNU General Public License, in which case the provisions of the GPL are
24 * required INSTEAD OF the above restrictions. (This clause is
25 * necessary due to a potential bad interaction between the GPL and
26 * the restrictions contained in a BSD-style copyright.)
28 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
29 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
30 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
31 * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
32 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
33 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
34 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
35 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
36 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
38 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
43 * (now, with legal B.S. out of the way.....)
45 * This routine gathers environmental noise from device drivers, etc.,
46 * and returns good random numbers, suitable for cryptographic use.
47 * Besides the obvious cryptographic uses, these numbers are also good
48 * for seeding TCP sequence numbers, and other places where it is
49 * desirable to have numbers which are not only random, but hard to
50 * predict by an attacker.
55 * Computers are very predictable devices. Hence it is extremely hard
56 * to produce truly random numbers on a computer --- as opposed to
57 * pseudo-random numbers, which can easily generated by using a
58 * algorithm. Unfortunately, it is very easy for attackers to guess
59 * the sequence of pseudo-random number generators, and for some
60 * applications this is not acceptable. So instead, we must try to
61 * gather "environmental noise" from the computer's environment, which
62 * must be hard for outside attackers to observe, and use that to
63 * generate random numbers. In a Unix environment, this is best done
64 * from inside the kernel.
66 * Sources of randomness from the environment include inter-keyboard
67 * timings, inter-interrupt timings from some interrupts, and other
68 * events which are both (a) non-deterministic and (b) hard for an
69 * outside observer to measure. Randomness from these sources are
70 * added to an "entropy pool", which is mixed using a CRC-like function.
71 * This is not cryptographically strong, but it is adequate assuming
72 * the randomness is not chosen maliciously, and it is fast enough that
73 * the overhead of doing it on every interrupt is very reasonable.
74 * As random bytes are mixed into the entropy pool, the routines keep
75 * an *estimate* of how many bits of randomness have been stored into
76 * the random number generator's internal state.
78 * When random bytes are desired, they are obtained by taking the SHA
79 * hash of the contents of the "entropy pool". The SHA hash avoids
80 * exposing the internal state of the entropy pool. It is believed to
81 * be computationally infeasible to derive any useful information
82 * about the input of SHA from its output. Even if it is possible to
83 * analyze SHA in some clever way, as long as the amount of data
84 * returned from the generator is less than the inherent entropy in
85 * the pool, the output data is totally unpredictable. For this
86 * reason, the routine decreases its internal estimate of how many
87 * bits of "true randomness" are contained in the entropy pool as it
88 * outputs random numbers.
90 * If this estimate goes to zero, the routine can still generate
91 * random numbers; however, an attacker may (at least in theory) be
92 * able to infer the future output of the generator from prior
93 * outputs. This requires successful cryptanalysis of SHA, which is
94 * not believed to be feasible, but there is a remote possibility.
95 * Nonetheless, these numbers should be useful for the vast majority
98 * Exported interfaces ---- output
99 * ===============================
101 * There are three exported interfaces; the first is one designed to
102 * be used from within the kernel:
104 * void get_random_bytes(void *buf, int nbytes);
106 * This interface will return the requested number of random bytes,
107 * and place it in the requested buffer.
109 * The two other interfaces are two character devices /dev/random and
110 * /dev/urandom. /dev/random is suitable for use when very high
111 * quality randomness is desired (for example, for key generation or
112 * one-time pads), as it will only return a maximum of the number of
113 * bits of randomness (as estimated by the random number generator)
114 * contained in the entropy pool.
116 * The /dev/urandom device does not have this limit, and will return
117 * as many bytes as are requested. As more and more random bytes are
118 * requested without giving time for the entropy pool to recharge,
119 * this will result in random numbers that are merely cryptographically
120 * strong. For many applications, however, this is acceptable.
122 * Exported interfaces ---- input
123 * ==============================
125 * The current exported interfaces for gathering environmental noise
126 * from the devices are:
128 * void add_input_randomness(unsigned int type, unsigned int code,
129 * unsigned int value);
130 * void add_interrupt_randomness(int irq);
132 * add_input_randomness() uses the input layer interrupt timing, as well as
133 * the event type information from the hardware.
135 * add_interrupt_randomness() uses the inter-interrupt timing as random
136 * inputs to the entropy pool. Note that not all interrupts are good
137 * sources of randomness! For example, the timer interrupts is not a
138 * good choice, because the periodicity of the interrupts is too
139 * regular, and hence predictable to an attacker. Disk interrupts are
140 * a better measure, since the timing of the disk interrupts are more
143 * All of these routines try to estimate how many bits of randomness a
144 * particular randomness source. They do this by keeping track of the
145 * first and second order deltas of the event timings.
147 * Ensuring unpredictability at system startup
148 * ============================================
150 * When any operating system starts up, it will go through a sequence
151 * of actions that are fairly predictable by an adversary, especially
152 * if the start-up does not involve interaction with a human operator.
153 * This reduces the actual number of bits of unpredictability in the
154 * entropy pool below the value in entropy_count. In order to
155 * counteract this effect, it helps to carry information in the
156 * entropy pool across shut-downs and start-ups. To do this, put the
157 * following lines an appropriate script which is run during the boot
160 * echo "Initializing random number generator..."
161 * random_seed=/var/run/random-seed
162 * # Carry a random seed from start-up to start-up
163 * # Load and then save the whole entropy pool
164 * if [ -f $random_seed ]; then
165 * cat $random_seed >/dev/urandom
169 * chmod 600 $random_seed
170 * dd if=/dev/urandom of=$random_seed count=1 bs=512
172 * and the following lines in an appropriate script which is run as
173 * the system is shutdown:
175 * # Carry a random seed from shut-down to start-up
176 * # Save the whole entropy pool
177 * echo "Saving random seed..."
178 * random_seed=/var/run/random-seed
180 * chmod 600 $random_seed
181 * dd if=/dev/urandom of=$random_seed count=1 bs=512
183 * For example, on most modern systems using the System V init
184 * scripts, such code fragments would be found in
185 * /etc/rc.d/init.d/random. On older Linux systems, the correct script
186 * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
188 * Effectively, these commands cause the contents of the entropy pool
189 * to be saved at shut-down time and reloaded into the entropy pool at
190 * start-up. (The 'dd' in the addition to the bootup script is to
191 * make sure that /etc/random-seed is different for every start-up,
192 * even if the system crashes without executing rc.0.) Even with
193 * complete knowledge of the start-up activities, predicting the state
194 * of the entropy pool requires knowledge of the previous history of
197 * Configuring the /dev/random driver under Linux
198 * ==============================================
200 * The /dev/random driver under Linux uses minor numbers 8 and 9 of
201 * the /dev/mem major number (#1). So if your system does not have
202 * /dev/random and /dev/urandom created already, they can be created
203 * by using the commands:
205 * mknod /dev/random c 1 8
206 * mknod /dev/urandom c 1 9
211 * Ideas for constructing this random number generator were derived
212 * from Pretty Good Privacy's random number generator, and from private
213 * discussions with Phil Karn. Colin Plumb provided a faster random
214 * number generator, which speed up the mixing function of the entropy
215 * pool, taken from PGPfone. Dale Worley has also contributed many
216 * useful ideas and suggestions to improve this driver.
218 * Any flaws in the design are solely my responsibility, and should
219 * not be attributed to the Phil, Colin, or any of authors of PGP.
221 * Further background information on this topic may be obtained from
222 * RFC 1750, "Randomness Recommendations for Security", by Donald
223 * Eastlake, Steve Crocker, and Jeff Schiller.
226 #include <linux/utsname.h>
227 #include <linux/module.h>
228 #include <linux/kernel.h>
229 #include <linux/major.h>
230 #include <linux/string.h>
231 #include <linux/fcntl.h>
232 #include <linux/slab.h>
233 #include <linux/random.h>
234 #include <linux/poll.h>
235 #include <linux/init.h>
236 #include <linux/fs.h>
237 #include <linux/genhd.h>
238 #include <linux/interrupt.h>
239 #include <linux/spinlock.h>
240 #include <linux/percpu.h>
241 #include <linux/cryptohash.h>
243 #include <asm/processor.h>
244 #include <asm/uaccess.h>
249 * Configuration information
251 #define INPUT_POOL_WORDS 128
252 #define OUTPUT_POOL_WORDS 32
253 #define SEC_XFER_SIZE 512
256 * The minimum number of bits of entropy before we wake up a read on
257 * /dev/random. Should be enough to do a significant reseed.
259 static int random_read_wakeup_thresh = 64;
262 * If the entropy count falls under this number of bits, then we
263 * should wake up processes which are selecting or polling on write
264 * access to /dev/random.
266 static int random_write_wakeup_thresh = 128;
269 * When the input pool goes over trickle_thresh, start dropping most
270 * samples to avoid wasting CPU time and reduce lock contention.
273 static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;
275 static DEFINE_PER_CPU(int, trickle_count);
278 * A pool of size .poolwords is stirred with a primitive polynomial
279 * of degree .poolwords over GF(2). The taps for various sizes are
280 * defined below. They are chosen to be evenly spaced (minimum RMS
281 * distance from evenly spaced; the numbers in the comments are a
282 * scaled squared error sum) except for the last tap, which is 1 to
283 * get the twisting happening as fast as possible.
285 static struct poolinfo {
287 int tap1, tap2, tap3, tap4, tap5;
288 } poolinfo_table[] = {
289 /* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */
290 { 128, 103, 76, 51, 25, 1 },
291 /* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */
292 { 32, 26, 20, 14, 7, 1 },
294 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */
295 { 2048, 1638, 1231, 819, 411, 1 },
297 /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */
298 { 1024, 817, 615, 412, 204, 1 },
300 /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */
301 { 1024, 819, 616, 410, 207, 2 },
303 /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */
304 { 512, 411, 308, 208, 104, 1 },
306 /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */
307 { 512, 409, 307, 206, 102, 2 },
308 /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */
309 { 512, 409, 309, 205, 103, 2 },
311 /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */
312 { 256, 205, 155, 101, 52, 1 },
314 /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */
315 { 128, 103, 78, 51, 27, 2 },
317 /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */
318 { 64, 52, 39, 26, 14, 1 },
322 #define POOLBITS poolwords*32
323 #define POOLBYTES poolwords*4
326 * For the purposes of better mixing, we use the CRC-32 polynomial as
327 * well to make a twisted Generalized Feedback Shift Reigster
329 * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM
330 * Transactions on Modeling and Computer Simulation 2(3):179-194.
331 * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators
332 * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266)
334 * Thanks to Colin Plumb for suggesting this.
336 * We have not analyzed the resultant polynomial to prove it primitive;
337 * in fact it almost certainly isn't. Nonetheless, the irreducible factors
338 * of a random large-degree polynomial over GF(2) are more than large enough
339 * that periodicity is not a concern.
341 * The input hash is much less sensitive than the output hash. All
342 * that we want of it is that it be a good non-cryptographic hash;
343 * i.e. it not produce collisions when fed "random" data of the sort
344 * we expect to see. As long as the pool state differs for different
345 * inputs, we have preserved the input entropy and done a good job.
346 * The fact that an intelligent attacker can construct inputs that
347 * will produce controlled alterations to the pool's state is not
348 * important because we don't consider such inputs to contribute any
349 * randomness. The only property we need with respect to them is that
350 * the attacker can't increase his/her knowledge of the pool's state.
351 * Since all additions are reversible (knowing the final state and the
352 * input, you can reconstruct the initial state), if an attacker has
353 * any uncertainty about the initial state, he/she can only shuffle
354 * that uncertainty about, but never cause any collisions (which would
355 * decrease the uncertainty).
357 * The chosen system lets the state of the pool be (essentially) the input
358 * modulo the generator polymnomial. Now, for random primitive polynomials,
359 * this is a universal class of hash functions, meaning that the chance
360 * of a collision is limited by the attacker's knowledge of the generator
361 * polynomail, so if it is chosen at random, an attacker can never force
362 * a collision. Here, we use a fixed polynomial, but we *can* assume that
363 * ###--> it is unknown to the processes generating the input entropy. <-###
364 * Because of this important property, this is a good, collision-resistant
365 * hash; hash collisions will occur no more often than chance.
369 * Static global variables
371 static DECLARE_WAIT_QUEUE_HEAD(random_read_wait);
372 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
376 module_param(debug, bool, 0644);
377 #define DEBUG_ENT(fmt, arg...) do { \
379 printk(KERN_DEBUG "random %04d %04d %04d: " \
381 input_pool.entropy_count,\
382 blocking_pool.entropy_count,\
383 nonblocking_pool.entropy_count,\
386 #define DEBUG_ENT(fmt, arg...) do {} while (0)
389 /**********************************************************************
391 * OS independent entropy store. Here are the functions which handle
392 * storing entropy in an entropy pool.
394 **********************************************************************/
396 struct entropy_store;
397 struct entropy_store {
398 /* read-only data: */
399 struct poolinfo *poolinfo;
403 struct entropy_store *pull;
405 /* read-write data: */
412 static __u32 input_pool_data[INPUT_POOL_WORDS];
413 static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
414 static __u32 nonblocking_pool_data[OUTPUT_POOL_WORDS];
416 static struct entropy_store input_pool = {
417 .poolinfo = &poolinfo_table[0],
420 .lock = __SPIN_LOCK_UNLOCKED(&input_pool.lock),
421 .pool = input_pool_data
424 static struct entropy_store blocking_pool = {
425 .poolinfo = &poolinfo_table[1],
429 .lock = __SPIN_LOCK_UNLOCKED(&blocking_pool.lock),
430 .pool = blocking_pool_data
433 static struct entropy_store nonblocking_pool = {
434 .poolinfo = &poolinfo_table[1],
435 .name = "nonblocking",
437 .lock = __SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),
438 .pool = nonblocking_pool_data
442 * This function adds a byte into the entropy "pool". It does not
443 * update the entropy estimate. The caller should call
444 * credit_entropy_store if this is appropriate.
446 * The pool is stirred with a primitive polynomial of the appropriate
447 * degree, and then twisted. We twist by three bits at a time because
448 * it's cheap to do so and helps slightly in the expected case where
449 * the entropy is concentrated in the low-order bits.
451 static void __add_entropy_words(struct entropy_store *r, const __u32 *in,
452 int nwords, __u32 out[16])
454 static __u32 const twist_table[8] = {
455 0x00000000, 0x3b6e20c8, 0x76dc4190, 0x4db26158,
456 0xedb88320, 0xd6d6a3e8, 0x9b64c2b0, 0xa00ae278 };
457 unsigned long i, j, tap1, tap2, tap3, tap4, tap5;
459 int wordmask = r->poolinfo->poolwords - 1;
463 /* Taps are constant, so we can load them without holding r->lock. */
464 tap1 = r->poolinfo->tap1;
465 tap2 = r->poolinfo->tap2;
466 tap3 = r->poolinfo->tap3;
467 tap4 = r->poolinfo->tap4;
468 tap5 = r->poolinfo->tap5;
470 spin_lock_irqsave(&r->lock, flags);
471 input_rotate = r->input_rotate;
475 w = rol32(*in++, input_rotate & 31);
476 i = (i - 1) & wordmask;
478 /* XOR in the various taps */
480 w ^= r->pool[(i + tap1) & wordmask];
481 w ^= r->pool[(i + tap2) & wordmask];
482 w ^= r->pool[(i + tap3) & wordmask];
483 w ^= r->pool[(i + tap4) & wordmask];
484 w ^= r->pool[(i + tap5) & wordmask];
486 /* Mix the result back in with a twist */
487 r->pool[i] = (w >> 3) ^ twist_table[w & 7];
490 * Normally, we add 7 bits of rotation to the pool.
491 * At the beginning of the pool, add an extra 7 bits
492 * rotation, so that successive passes spread the
493 * input bits across the pool evenly.
495 input_rotate += i ? 7 : 14;
498 r->input_rotate = input_rotate;
502 for (j = 0; j < 16; j++)
503 out[j] = r->pool[(i - j) & wordmask];
505 spin_unlock_irqrestore(&r->lock, flags);
508 static inline void add_entropy_words(struct entropy_store *r, const __u32 *in,
511 __add_entropy_words(r, in, nwords, NULL);
515 * Credit (or debit) the entropy store with n bits of entropy
517 static void credit_entropy_store(struct entropy_store *r, int nbits)
521 spin_lock_irqsave(&r->lock, flags);
523 if (r->entropy_count + nbits < 0) {
524 DEBUG_ENT("negative entropy/overflow (%d+%d)\n",
525 r->entropy_count, nbits);
526 r->entropy_count = 0;
527 } else if (r->entropy_count + nbits > r->poolinfo->POOLBITS) {
528 r->entropy_count = r->poolinfo->POOLBITS;
530 r->entropy_count += nbits;
532 DEBUG_ENT("added %d entropy credits to %s\n",
536 /* should we wake readers? */
537 if (r == &input_pool && r->entropy_count >= random_read_wakeup_thresh)
538 wake_up_interruptible(&random_read_wait);
540 spin_unlock_irqrestore(&r->lock, flags);
543 /*********************************************************************
545 * Entropy input management
547 *********************************************************************/
549 /* There is one of these per entropy source */
550 struct timer_rand_state {
552 long last_delta, last_delta2;
553 unsigned dont_count_entropy:1;
556 static struct timer_rand_state input_timer_state;
557 static struct timer_rand_state *irq_timer_state[NR_IRQS];
560 * This function adds entropy to the entropy "pool" by using timing
561 * delays. It uses the timer_rand_state structure to make an estimate
562 * of how many bits of entropy this call has added to the pool.
564 * The number "num" is also added to the pool - it should somehow describe
565 * the type of event which just happened. This is currently 0-255 for
566 * keyboard scan codes, and 256 upwards for interrupts.
569 static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
576 long delta, delta2, delta3;
579 /* if over the trickle threshold, use only 1 in 4096 samples */
580 if (input_pool.entropy_count > trickle_thresh &&
581 (__get_cpu_var(trickle_count)++ & 0xfff))
584 sample.jiffies = jiffies;
585 sample.cycles = get_cycles();
587 add_entropy_words(&input_pool, (u32 *)&sample, sizeof(sample)/4);
590 * Calculate number of bits of randomness we probably added.
591 * We take into account the first, second and third-order deltas
592 * in order to make our estimate.
595 if (!state->dont_count_entropy) {
596 delta = sample.jiffies - state->last_time;
597 state->last_time = sample.jiffies;
599 delta2 = delta - state->last_delta;
600 state->last_delta = delta;
602 delta3 = delta2 - state->last_delta2;
603 state->last_delta2 = delta2;
617 * delta is now minimum absolute delta.
618 * Round down by 1 bit on general principles,
619 * and limit entropy entimate to 12 bits.
621 credit_entropy_store(&input_pool,
622 min_t(int, fls(delta>>1), 11));
628 void add_input_randomness(unsigned int type, unsigned int code,
631 static unsigned char last_value;
633 /* ignore autorepeat and the like */
634 if (value == last_value)
637 DEBUG_ENT("input event\n");
639 add_timer_randomness(&input_timer_state,
640 (type << 4) ^ code ^ (code >> 4) ^ value);
642 EXPORT_SYMBOL_GPL(add_input_randomness);
644 void add_interrupt_randomness(int irq)
646 if (irq >= NR_IRQS || irq_timer_state[irq] == NULL)
649 DEBUG_ENT("irq event %d\n", irq);
650 add_timer_randomness(irq_timer_state[irq], 0x100 + irq);
654 void add_disk_randomness(struct gendisk *disk)
656 if (!disk || !disk->random)
658 /* first major is 1, so we get >= 0x200 here */
659 DEBUG_ENT("disk event %d:%d\n", disk->major, disk->first_minor);
661 add_timer_randomness(disk->random,
662 0x100 + MKDEV(disk->major, disk->first_minor));
666 #define EXTRACT_SIZE 10
668 /*********************************************************************
670 * Entropy extraction routines
672 *********************************************************************/
674 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
675 size_t nbytes, int min, int rsvd);
678 * This utility inline function is responsible for transfering entropy
679 * from the primary pool to the secondary extraction pool. We make
680 * sure we pull enough for a 'catastrophic reseed'.
682 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
684 __u32 tmp[OUTPUT_POOL_WORDS];
686 if (r->pull && r->entropy_count < nbytes * 8 &&
687 r->entropy_count < r->poolinfo->POOLBITS) {
688 /* If we're limited, always leave two wakeup worth's BITS */
689 int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
692 /* pull at least as many as BYTES as wakeup BITS */
693 bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
694 /* but never more than the buffer size */
695 bytes = min_t(int, bytes, sizeof(tmp));
697 DEBUG_ENT("going to reseed %s with %d bits "
698 "(%d of %d requested)\n",
699 r->name, bytes * 8, nbytes * 8, r->entropy_count);
701 bytes = extract_entropy(r->pull, tmp, bytes,
702 random_read_wakeup_thresh / 8, rsvd);
703 add_entropy_words(r, tmp, (bytes + 3) / 4);
704 credit_entropy_store(r, bytes*8);
709 * These functions extracts randomness from the "entropy pool", and
710 * returns it in a buffer.
712 * The min parameter specifies the minimum amount we can pull before
713 * failing to avoid races that defeat catastrophic reseeding while the
714 * reserved parameter indicates how much entropy we must leave in the
715 * pool after each pull to avoid starving other readers.
717 * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words.
720 static size_t account(struct entropy_store *r, size_t nbytes, int min,
725 BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
727 /* Hold lock while accounting */
728 spin_lock_irqsave(&r->lock, flags);
730 DEBUG_ENT("trying to extract %d bits from %s\n",
731 nbytes * 8, r->name);
733 /* Can we pull enough? */
734 if (r->entropy_count / 8 < min + reserved) {
737 /* If limited, never pull more than available */
738 if (r->limit && nbytes + reserved >= r->entropy_count / 8)
739 nbytes = r->entropy_count/8 - reserved;
741 if (r->entropy_count / 8 >= nbytes + reserved)
742 r->entropy_count -= nbytes*8;
744 r->entropy_count = reserved;
746 if (r->entropy_count < random_write_wakeup_thresh)
747 wake_up_interruptible(&random_write_wait);
750 DEBUG_ENT("debiting %d entropy credits from %s%s\n",
751 nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
753 spin_unlock_irqrestore(&r->lock, flags);
758 static void extract_buf(struct entropy_store *r, __u8 *out)
761 __u32 extract[16], hash[5], workspace[SHA_WORKSPACE_WORDS];
763 /* Generate a hash across the pool, 16 words (512 bits) at a time */
765 for (i = 0; i < r->poolinfo->poolwords; i += 16)
766 sha_transform(hash, (__u8 *)(r->pool + i), workspace);
769 * We mix the hash back into the pool to prevent backtracking
770 * attacks (where the attacker knows the state of the pool
771 * plus the current outputs, and attempts to find previous
772 * ouputs), unless the hash function can be inverted. By
773 * mixing at least a SHA1 worth of hash data back, we make
774 * brute-forcing the feedback as hard as brute-forcing the
777 __add_entropy_words(r, hash, 5, extract);
780 * To avoid duplicates, we atomically extract a portion of the
781 * pool while mixing, and hash one final time.
783 sha_transform(hash, (__u8 *)extract, workspace);
784 memset(extract, 0, sizeof(extract));
785 memset(workspace, 0, sizeof(workspace));
788 * In case the hash function has some recognizable output
789 * pattern, we fold it in half. Thus, we always feed back
790 * twice as much data as we output.
794 hash[2] ^= rol32(hash[2], 16);
795 memcpy(out, hash, EXTRACT_SIZE);
796 memset(hash, 0, sizeof(hash));
799 static ssize_t extract_entropy(struct entropy_store *r, void *buf,
800 size_t nbytes, int min, int reserved)
803 __u8 tmp[EXTRACT_SIZE];
805 xfer_secondary_pool(r, nbytes);
806 nbytes = account(r, nbytes, min, reserved);
810 i = min_t(int, nbytes, EXTRACT_SIZE);
817 /* Wipe data just returned from memory */
818 memset(tmp, 0, sizeof(tmp));
823 static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
827 __u8 tmp[EXTRACT_SIZE];
829 xfer_secondary_pool(r, nbytes);
830 nbytes = account(r, nbytes, 0, 0);
833 if (need_resched()) {
834 if (signal_pending(current)) {
843 i = min_t(int, nbytes, EXTRACT_SIZE);
844 if (copy_to_user(buf, tmp, i)) {
854 /* Wipe data just returned from memory */
855 memset(tmp, 0, sizeof(tmp));
861 * This function is the exported kernel interface. It returns some
862 * number of good random numbers, suitable for seeding TCP sequence
865 void get_random_bytes(void *buf, int nbytes)
867 extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
869 EXPORT_SYMBOL(get_random_bytes);
872 * init_std_data - initialize pool with system data
874 * @r: pool to initialize
876 * This function clears the pool's entropy count and mixes some system
877 * data into the pool to prepare it for use. The pool is not cleared
878 * as that can only decrease the entropy in the pool.
880 static void init_std_data(struct entropy_store *r)
885 spin_lock_irqsave(&r->lock, flags);
886 r->entropy_count = 0;
887 spin_unlock_irqrestore(&r->lock, flags);
889 now = ktime_get_real();
890 add_entropy_words(r, (__u32 *)&now, sizeof(now)/4);
891 add_entropy_words(r, (__u32 *)utsname(),
892 sizeof(*(utsname()))/4);
895 static int rand_initialize(void)
897 init_std_data(&input_pool);
898 init_std_data(&blocking_pool);
899 init_std_data(&nonblocking_pool);
902 module_init(rand_initialize);
904 void rand_initialize_irq(int irq)
906 struct timer_rand_state *state;
908 if (irq >= NR_IRQS || irq_timer_state[irq])
912 * If kzalloc returns null, we just won't use that entropy
915 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
917 irq_timer_state[irq] = state;
921 void rand_initialize_disk(struct gendisk *disk)
923 struct timer_rand_state *state;
926 * If kzalloc returns null, we just won't use that entropy
929 state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
931 disk->random = state;
936 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
938 ssize_t n, retval = 0, count = 0;
945 if (n > SEC_XFER_SIZE)
948 DEBUG_ENT("reading %d bits\n", n*8);
950 n = extract_entropy_user(&blocking_pool, buf, n);
952 DEBUG_ENT("read got %d bits (%d still needed)\n",
956 if (file->f_flags & O_NONBLOCK) {
961 DEBUG_ENT("sleeping?\n");
963 wait_event_interruptible(random_read_wait,
964 input_pool.entropy_count >=
965 random_read_wakeup_thresh);
967 DEBUG_ENT("awake\n");
969 if (signal_pending(current)) {
970 retval = -ERESTARTSYS;
984 break; /* This break makes the device work */
985 /* like a named pipe */
989 * If we gave the user some bytes, update the access time.
994 return (count ? count : retval);
998 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
1000 return extract_entropy_user(&nonblocking_pool, buf, nbytes);
1004 random_poll(struct file *file, poll_table * wait)
1008 poll_wait(file, &random_read_wait, wait);
1009 poll_wait(file, &random_write_wait, wait);
1011 if (input_pool.entropy_count >= random_read_wakeup_thresh)
1012 mask |= POLLIN | POLLRDNORM;
1013 if (input_pool.entropy_count < random_write_wakeup_thresh)
1014 mask |= POLLOUT | POLLWRNORM;
1019 write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
1023 const char __user *p = buffer;
1026 bytes = min(count, sizeof(buf));
1027 if (copy_from_user(&buf, p, bytes))
1033 add_entropy_words(r, buf, (bytes + 3) / 4);
1040 static ssize_t random_write(struct file *file, const char __user *buffer,
1041 size_t count, loff_t *ppos)
1044 struct inode *inode = file->f_path.dentry->d_inode;
1046 ret = write_pool(&blocking_pool, buffer, count);
1049 ret = write_pool(&nonblocking_pool, buffer, count);
1053 inode->i_mtime = current_fs_time(inode->i_sb);
1054 mark_inode_dirty(inode);
1055 return (ssize_t)count;
1058 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
1060 int size, ent_count;
1061 int __user *p = (int __user *)arg;
1066 /* inherently racy, no point locking */
1067 if (put_user(input_pool.entropy_count, p))
1070 case RNDADDTOENTCNT:
1071 if (!capable(CAP_SYS_ADMIN))
1073 if (get_user(ent_count, p))
1075 credit_entropy_store(&input_pool, ent_count);
1078 if (!capable(CAP_SYS_ADMIN))
1080 if (get_user(ent_count, p++))
1084 if (get_user(size, p++))
1086 retval = write_pool(&input_pool, (const char __user *)p,
1090 credit_entropy_store(&input_pool, ent_count);
1094 /* Clear the entropy pool counters. */
1095 if (!capable(CAP_SYS_ADMIN))
1104 const struct file_operations random_fops = {
1105 .read = random_read,
1106 .write = random_write,
1107 .poll = random_poll,
1108 .unlocked_ioctl = random_ioctl,
1111 const struct file_operations urandom_fops = {
1112 .read = urandom_read,
1113 .write = random_write,
1114 .unlocked_ioctl = random_ioctl,
1117 /***************************************************************
1118 * Random UUID interface
1120 * Used here for a Boot ID, but can be useful for other kernel
1122 ***************************************************************/
1125 * Generate random UUID
1127 void generate_random_uuid(unsigned char uuid_out[16])
1129 get_random_bytes(uuid_out, 16);
1130 /* Set UUID version to 4 --- truely random generation */
1131 uuid_out[6] = (uuid_out[6] & 0x0F) | 0x40;
1132 /* Set the UUID variant to DCE */
1133 uuid_out[8] = (uuid_out[8] & 0x3F) | 0x80;
1135 EXPORT_SYMBOL(generate_random_uuid);
1137 /********************************************************************
1141 ********************************************************************/
1143 #ifdef CONFIG_SYSCTL
1145 #include <linux/sysctl.h>
1147 static int min_read_thresh = 8, min_write_thresh;
1148 static int max_read_thresh = INPUT_POOL_WORDS * 32;
1149 static int max_write_thresh = INPUT_POOL_WORDS * 32;
1150 static char sysctl_bootid[16];
1153 * These functions is used to return both the bootid UUID, and random
1154 * UUID. The difference is in whether table->data is NULL; if it is,
1155 * then a new UUID is generated and returned to the user.
1157 * If the user accesses this via the proc interface, it will be returned
1158 * as an ASCII string in the standard UUID format. If accesses via the
1159 * sysctl system call, it is returned as 16 bytes of binary data.
1161 static int proc_do_uuid(ctl_table *table, int write, struct file *filp,
1162 void __user *buffer, size_t *lenp, loff_t *ppos)
1164 ctl_table fake_table;
1165 unsigned char buf[64], tmp_uuid[16], *uuid;
1173 generate_random_uuid(uuid);
1175 sprintf(buf, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
1176 "%02x%02x%02x%02x%02x%02x",
1177 uuid[0], uuid[1], uuid[2], uuid[3],
1178 uuid[4], uuid[5], uuid[6], uuid[7],
1179 uuid[8], uuid[9], uuid[10], uuid[11],
1180 uuid[12], uuid[13], uuid[14], uuid[15]);
1181 fake_table.data = buf;
1182 fake_table.maxlen = sizeof(buf);
1184 return proc_dostring(&fake_table, write, filp, buffer, lenp, ppos);
1187 static int uuid_strategy(ctl_table *table, int __user *name, int nlen,
1188 void __user *oldval, size_t __user *oldlenp,
1189 void __user *newval, size_t newlen)
1191 unsigned char tmp_uuid[16], *uuid;
1194 if (!oldval || !oldlenp)
1203 generate_random_uuid(uuid);
1205 if (get_user(len, oldlenp))
1210 if (copy_to_user(oldval, uuid, len) ||
1211 put_user(len, oldlenp))
1217 static int sysctl_poolsize = INPUT_POOL_WORDS * 32;
1218 ctl_table random_table[] = {
1220 .ctl_name = RANDOM_POOLSIZE,
1221 .procname = "poolsize",
1222 .data = &sysctl_poolsize,
1223 .maxlen = sizeof(int),
1225 .proc_handler = &proc_dointvec,
1228 .ctl_name = RANDOM_ENTROPY_COUNT,
1229 .procname = "entropy_avail",
1230 .maxlen = sizeof(int),
1232 .proc_handler = &proc_dointvec,
1233 .data = &input_pool.entropy_count,
1236 .ctl_name = RANDOM_READ_THRESH,
1237 .procname = "read_wakeup_threshold",
1238 .data = &random_read_wakeup_thresh,
1239 .maxlen = sizeof(int),
1241 .proc_handler = &proc_dointvec_minmax,
1242 .strategy = &sysctl_intvec,
1243 .extra1 = &min_read_thresh,
1244 .extra2 = &max_read_thresh,
1247 .ctl_name = RANDOM_WRITE_THRESH,
1248 .procname = "write_wakeup_threshold",
1249 .data = &random_write_wakeup_thresh,
1250 .maxlen = sizeof(int),
1252 .proc_handler = &proc_dointvec_minmax,
1253 .strategy = &sysctl_intvec,
1254 .extra1 = &min_write_thresh,
1255 .extra2 = &max_write_thresh,
1258 .ctl_name = RANDOM_BOOT_ID,
1259 .procname = "boot_id",
1260 .data = &sysctl_bootid,
1263 .proc_handler = &proc_do_uuid,
1264 .strategy = &uuid_strategy,
1267 .ctl_name = RANDOM_UUID,
1271 .proc_handler = &proc_do_uuid,
1272 .strategy = &uuid_strategy,
1276 #endif /* CONFIG_SYSCTL */
1278 /********************************************************************
1280 * Random funtions for networking
1282 ********************************************************************/
1285 * TCP initial sequence number picking. This uses the random number
1286 * generator to pick an initial secret value. This value is hashed
1287 * along with the TCP endpoint information to provide a unique
1288 * starting point for each pair of TCP endpoints. This defeats
1289 * attacks which rely on guessing the initial TCP sequence number.
1290 * This algorithm was suggested by Steve Bellovin.
1292 * Using a very strong hash was taking an appreciable amount of the total
1293 * TCP connection establishment time, so this is a weaker hash,
1294 * compensated for by changing the secret periodically.
1297 /* F, G and H are basic MD4 functions: selection, majority, parity */
1298 #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
1299 #define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
1300 #define H(x, y, z) ((x) ^ (y) ^ (z))
1303 * The generic round function. The application is so specific that
1304 * we don't bother protecting all the arguments with parens, as is generally
1305 * good macro practice, in favor of extra legibility.
1306 * Rotation is separate from addition to prevent recomputation
1308 #define ROUND(f, a, b, c, d, x, s) \
1309 (a += f(b, c, d) + x, a = (a << s) | (a >> (32 - s)))
1311 #define K2 013240474631UL
1312 #define K3 015666365641UL
1314 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
1316 static __u32 twothirdsMD4Transform(__u32 const buf[4], __u32 const in[12])
1318 __u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
1321 ROUND(F, a, b, c, d, in[ 0] + K1, 3);
1322 ROUND(F, d, a, b, c, in[ 1] + K1, 7);
1323 ROUND(F, c, d, a, b, in[ 2] + K1, 11);
1324 ROUND(F, b, c, d, a, in[ 3] + K1, 19);
1325 ROUND(F, a, b, c, d, in[ 4] + K1, 3);
1326 ROUND(F, d, a, b, c, in[ 5] + K1, 7);
1327 ROUND(F, c, d, a, b, in[ 6] + K1, 11);
1328 ROUND(F, b, c, d, a, in[ 7] + K1, 19);
1329 ROUND(F, a, b, c, d, in[ 8] + K1, 3);
1330 ROUND(F, d, a, b, c, in[ 9] + K1, 7);
1331 ROUND(F, c, d, a, b, in[10] + K1, 11);
1332 ROUND(F, b, c, d, a, in[11] + K1, 19);
1335 ROUND(G, a, b, c, d, in[ 1] + K2, 3);
1336 ROUND(G, d, a, b, c, in[ 3] + K2, 5);
1337 ROUND(G, c, d, a, b, in[ 5] + K2, 9);
1338 ROUND(G, b, c, d, a, in[ 7] + K2, 13);
1339 ROUND(G, a, b, c, d, in[ 9] + K2, 3);
1340 ROUND(G, d, a, b, c, in[11] + K2, 5);
1341 ROUND(G, c, d, a, b, in[ 0] + K2, 9);
1342 ROUND(G, b, c, d, a, in[ 2] + K2, 13);
1343 ROUND(G, a, b, c, d, in[ 4] + K2, 3);
1344 ROUND(G, d, a, b, c, in[ 6] + K2, 5);
1345 ROUND(G, c, d, a, b, in[ 8] + K2, 9);
1346 ROUND(G, b, c, d, a, in[10] + K2, 13);
1349 ROUND(H, a, b, c, d, in[ 3] + K3, 3);
1350 ROUND(H, d, a, b, c, in[ 7] + K3, 9);
1351 ROUND(H, c, d, a, b, in[11] + K3, 11);
1352 ROUND(H, b, c, d, a, in[ 2] + K3, 15);
1353 ROUND(H, a, b, c, d, in[ 6] + K3, 3);
1354 ROUND(H, d, a, b, c, in[10] + K3, 9);
1355 ROUND(H, c, d, a, b, in[ 1] + K3, 11);
1356 ROUND(H, b, c, d, a, in[ 5] + K3, 15);
1357 ROUND(H, a, b, c, d, in[ 9] + K3, 3);
1358 ROUND(H, d, a, b, c, in[ 0] + K3, 9);
1359 ROUND(H, c, d, a, b, in[ 4] + K3, 11);
1360 ROUND(H, b, c, d, a, in[ 8] + K3, 15);
1362 return buf[1] + b; /* "most hashed" word */
1363 /* Alternative: return sum of all words? */
1375 /* This should not be decreased so low that ISNs wrap too fast. */
1376 #define REKEY_INTERVAL (300 * HZ)
1378 * Bit layout of the tcp sequence numbers (before adding current time):
1379 * bit 24-31: increased after every key exchange
1380 * bit 0-23: hash(source,dest)
1382 * The implementation is similar to the algorithm described
1383 * in the Appendix of RFC 1185, except that
1384 * - it uses a 1 MHz clock instead of a 250 kHz clock
1385 * - it performs a rekey every 5 minutes, which is equivalent
1386 * to a (source,dest) tulple dependent forward jump of the
1387 * clock by 0..2^(HASH_BITS+1)
1389 * Thus the average ISN wraparound time is 68 minutes instead of
1392 * SMP cleanup and lock avoidance with poor man's RCU.
1393 * Manfred Spraul <manfred@colorfullife.com>
1396 #define COUNT_BITS 8
1397 #define COUNT_MASK ((1 << COUNT_BITS) - 1)
1398 #define HASH_BITS 24
1399 #define HASH_MASK ((1 << HASH_BITS) - 1)
1401 static struct keydata {
1402 __u32 count; /* already shifted to the final position */
1404 } ____cacheline_aligned ip_keydata[2];
1406 static unsigned int ip_cnt;
1408 static void rekey_seq_generator(struct work_struct *work);
1410 static DECLARE_DELAYED_WORK(rekey_work, rekey_seq_generator);
1414 * The ISN generation runs lockless - it's just a hash over random data.
1415 * State changes happen every 5 minutes when the random key is replaced.
1416 * Synchronization is performed by having two copies of the hash function
1417 * state and rekey_seq_generator always updates the inactive copy.
1418 * The copy is then activated by updating ip_cnt.
1419 * The implementation breaks down if someone blocks the thread
1420 * that processes SYN requests for more than 5 minutes. Should never
1421 * happen, and even if that happens only a not perfectly compliant
1422 * ISN is generated, nothing fatal.
1424 static void rekey_seq_generator(struct work_struct *work)
1426 struct keydata *keyptr = &ip_keydata[1 ^ (ip_cnt & 1)];
1428 get_random_bytes(keyptr->secret, sizeof(keyptr->secret));
1429 keyptr->count = (ip_cnt & COUNT_MASK) << HASH_BITS;
1432 schedule_delayed_work(&rekey_work, REKEY_INTERVAL);
1435 static inline struct keydata *get_keyptr(void)
1437 struct keydata *keyptr = &ip_keydata[ip_cnt & 1];
1444 static __init int seqgen_init(void)
1446 rekey_seq_generator(NULL);
1449 late_initcall(seqgen_init);
1451 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
1452 __u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,
1453 __be16 sport, __be16 dport)
1457 struct keydata *keyptr = get_keyptr();
1459 /* The procedure is the same as for IPv4, but addresses are longer.
1460 * Thus we must use twothirdsMD4Transform.
1463 memcpy(hash, saddr, 16);
1464 hash[4] = ((__force u16)sport << 16) + (__force u16)dport;
1465 memcpy(&hash[5], keyptr->secret, sizeof(__u32) * 7);
1467 seq = twothirdsMD4Transform((const __u32 *)daddr, hash) & HASH_MASK;
1468 seq += keyptr->count;
1470 seq += ktime_to_ns(ktime_get_real());
1474 EXPORT_SYMBOL(secure_tcpv6_sequence_number);
1477 /* The code below is shamelessly stolen from secure_tcp_sequence_number().
1478 * All blames to Andrey V. Savochkin <saw@msu.ru>.
1480 __u32 secure_ip_id(__be32 daddr)
1482 struct keydata *keyptr;
1485 keyptr = get_keyptr();
1488 * Pick a unique starting offset for each IP destination.
1489 * The dest ip address is placed in the starting vector,
1490 * which is then hashed with random data.
1492 hash[0] = (__force __u32)daddr;
1493 hash[1] = keyptr->secret[9];
1494 hash[2] = keyptr->secret[10];
1495 hash[3] = keyptr->secret[11];
1497 return half_md4_transform(hash, keyptr->secret);
1502 __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
1503 __be16 sport, __be16 dport)
1507 struct keydata *keyptr = get_keyptr();
1510 * Pick a unique starting offset for each TCP connection endpoints
1511 * (saddr, daddr, sport, dport).
1512 * Note that the words are placed into the starting vector, which is
1513 * then mixed with a partial MD4 over random data.
1515 hash[0] = (__force u32)saddr;
1516 hash[1] = (__force u32)daddr;
1517 hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
1518 hash[3] = keyptr->secret[11];
1520 seq = half_md4_transform(hash, keyptr->secret) & HASH_MASK;
1521 seq += keyptr->count;
1523 * As close as possible to RFC 793, which
1524 * suggests using a 250 kHz clock.
1525 * Further reading shows this assumes 2 Mb/s networks.
1526 * For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
1527 * For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
1528 * we also need to limit the resolution so that the u32 seq
1529 * overlaps less than one time per MSL (2 minutes).
1530 * Choosing a clock of 64 ns period is OK. (period of 274 s)
1532 seq += ktime_to_ns(ktime_get_real()) >> 6;
1537 /* Generate secure starting point for ephemeral IPV4 transport port search */
1538 u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
1540 struct keydata *keyptr = get_keyptr();
1544 * Pick a unique starting offset for each ephemeral port search
1545 * (saddr, daddr, dport) and 48bits of random data.
1547 hash[0] = (__force u32)saddr;
1548 hash[1] = (__force u32)daddr;
1549 hash[2] = (__force u32)dport ^ keyptr->secret[10];
1550 hash[3] = keyptr->secret[11];
1552 return half_md4_transform(hash, keyptr->secret);
1555 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
1556 u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
1559 struct keydata *keyptr = get_keyptr();
1562 memcpy(hash, saddr, 16);
1563 hash[4] = (__force u32)dport;
1564 memcpy(&hash[5], keyptr->secret, sizeof(__u32) * 7);
1566 return twothirdsMD4Transform((const __u32 *)daddr, hash);
1570 #if defined(CONFIG_IP_DCCP) || defined(CONFIG_IP_DCCP_MODULE)
1571 /* Similar to secure_tcp_sequence_number but generate a 48 bit value
1572 * bit's 32-47 increase every key exchange
1573 * 0-31 hash(source, dest)
1575 u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
1576 __be16 sport, __be16 dport)
1580 struct keydata *keyptr = get_keyptr();
1582 hash[0] = (__force u32)saddr;
1583 hash[1] = (__force u32)daddr;
1584 hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
1585 hash[3] = keyptr->secret[11];
1587 seq = half_md4_transform(hash, keyptr->secret);
1588 seq |= ((u64)keyptr->count) << (32 - HASH_BITS);
1590 seq += ktime_to_ns(ktime_get_real());
1591 seq &= (1ull << 48) - 1;
1595 EXPORT_SYMBOL(secure_dccp_sequence_number);
1598 #endif /* CONFIG_INET */
1602 * Get a random word for internal kernel use only. Similar to urandom but
1603 * with the goal of minimal entropy pool depletion. As a result, the random
1604 * value is not cryptographically secure but for several uses the cost of
1605 * depleting entropy is too high
1607 unsigned int get_random_int(void)
1610 * Use IP's RNG. It suits our purpose perfectly: it re-keys itself
1611 * every second, from the entropy pool (and thus creates a limited
1612 * drain on it), and uses halfMD4Transform within the second. We
1613 * also mix it with jiffies and the PID:
1615 return secure_ip_id((__force __be32)(current->pid + jiffies));
1619 * randomize_range() returns a start address such that
1621 * [...... <range> .....]
1624 * a <range> with size "len" starting at the return value is inside in the
1625 * area defined by [start, end], but is otherwise randomized.
1628 randomize_range(unsigned long start, unsigned long end, unsigned long len)
1630 unsigned long range = end - len - start;
1632 if (end <= start + len)
1634 return PAGE_ALIGN(get_random_int() % range + start);