1/*
2 * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License").  You may not use
5 * this file except in compliance with the License.  You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include <stdio.h>
11#include <time.h>
12#include "internal/cryptlib.h"
13#include <openssl/opensslconf.h>
14#include "crypto/rand.h"
15#include <openssl/engine.h>
16#include "internal/thread_once.h"
17#include "crypto/rand_pool.h"
18
19/*
20 * Allocate memory and initialize a new random pool
21 */
22RAND_POOL *ossl_rand_pool_new(int entropy_requested, int secure,
23                              size_t min_len, size_t max_len)
24{
25    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));
26    size_t min_alloc_size = RAND_POOL_MIN_ALLOCATION(secure);
27
28    if (pool == NULL) {
29        ERR_raise(ERR_LIB_RAND, ERR_R_MALLOC_FAILURE);
30        return NULL;
31    }
32
33    pool->min_len = min_len;
34    pool->max_len = (max_len > RAND_POOL_MAX_LENGTH) ?
35        RAND_POOL_MAX_LENGTH : max_len;
36    pool->alloc_len = min_len < min_alloc_size ? min_alloc_size : min_len;
37    if (pool->alloc_len > pool->max_len)
38        pool->alloc_len = pool->max_len;
39
40    if (secure)
41        pool->buffer = OPENSSL_secure_zalloc(pool->alloc_len);
42    else
43        pool->buffer = OPENSSL_zalloc(pool->alloc_len);
44
45    if (pool->buffer == NULL) {
46        ERR_raise(ERR_LIB_RAND, ERR_R_MALLOC_FAILURE);
47        goto err;
48    }
49
50    pool->entropy_requested = entropy_requested;
51    pool->secure = secure;
52    return pool;
53
54err:
55    OPENSSL_free(pool);
56    return NULL;
57}
58
59/*
60 * Attach new random pool to the given buffer
61 *
62 * This function is intended to be used only for feeding random data
63 * provided by RAND_add() and RAND_seed() into the <master> DRBG.
64 */
65RAND_POOL *ossl_rand_pool_attach(const unsigned char *buffer, size_t len,
66                                 size_t entropy)
67{
68    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));
69
70    if (pool == NULL) {
71        ERR_raise(ERR_LIB_RAND, ERR_R_MALLOC_FAILURE);
72        return NULL;
73    }
74
75    /*
76     * The const needs to be cast away, but attached buffers will not be
77     * modified (in contrary to allocated buffers which are zeroed and
78     * freed in the end).
79     */
80    pool->buffer = (unsigned char *) buffer;
81    pool->len = len;
82
83    pool->attached = 1;
84
85    pool->min_len = pool->max_len = pool->alloc_len = pool->len;
86    pool->entropy = entropy;
87
88    return pool;
89}
90
91/*
92 * Free |pool|, securely erasing its buffer.
93 */
94void ossl_rand_pool_free(RAND_POOL *pool)
95{
96    if (pool == NULL)
97        return;
98
99    /*
100     * Although it would be advisable from a cryptographical viewpoint,
101     * we are not allowed to clear attached buffers, since they are passed
102     * to ossl_rand_pool_attach() as `const unsigned char*`.
103     * (see corresponding comment in ossl_rand_pool_attach()).
104     */
105    if (!pool->attached) {
106        if (pool->secure)
107            OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);
108        else
109            OPENSSL_clear_free(pool->buffer, pool->alloc_len);
110    }
111
112    OPENSSL_free(pool);
113}
114
115/*
116 * Return the |pool|'s buffer to the caller (readonly).
117 */
118const unsigned char *ossl_rand_pool_buffer(RAND_POOL *pool)
119{
120    return pool->buffer;
121}
122
123/*
124 * Return the |pool|'s entropy to the caller.
125 */
126size_t ossl_rand_pool_entropy(RAND_POOL *pool)
127{
128    return pool->entropy;
129}
130
131/*
132 * Return the |pool|'s buffer length to the caller.
133 */
134size_t ossl_rand_pool_length(RAND_POOL *pool)
135{
136    return pool->len;
137}
138
139/*
140 * Detach the |pool| buffer and return it to the caller.
141 * It's the responsibility of the caller to free the buffer
142 * using OPENSSL_secure_clear_free() or to re-attach it
143 * again to the pool using ossl_rand_pool_reattach().
144 */
145unsigned char *ossl_rand_pool_detach(RAND_POOL *pool)
146{
147    unsigned char *ret = pool->buffer;
148    pool->buffer = NULL;
149    pool->entropy = 0;
150    return ret;
151}
152
153/*
154 * Re-attach the |pool| buffer. It is only allowed to pass
155 * the |buffer| which was previously detached from the same pool.
156 */
157void ossl_rand_pool_reattach(RAND_POOL *pool, unsigned char *buffer)
158{
159    pool->buffer = buffer;
160    OPENSSL_cleanse(pool->buffer, pool->len);
161    pool->len = 0;
162}
163
164/*
165 * If |entropy_factor| bits contain 1 bit of entropy, how many bytes does one
166 * need to obtain at least |bits| bits of entropy?
167 */
168#define ENTROPY_TO_BYTES(bits, entropy_factor) \
169    (((bits) * (entropy_factor) + 7) / 8)
170
171
172/*
173 * Checks whether the |pool|'s entropy is available to the caller.
174 * This is the case when entropy count and buffer length are high enough.
175 * Returns
176 *
177 *  |entropy|  if the entropy count and buffer size is large enough
178 *      0      otherwise
179 */
180size_t ossl_rand_pool_entropy_available(RAND_POOL *pool)
181{
182    if (pool->entropy < pool->entropy_requested)
183        return 0;
184
185    if (pool->len < pool->min_len)
186        return 0;
187
188    return pool->entropy;
189}
190
191/*
192 * Returns the (remaining) amount of entropy needed to fill
193 * the random pool.
194 */
195
196size_t ossl_rand_pool_entropy_needed(RAND_POOL *pool)
197{
198    if (pool->entropy < pool->entropy_requested)
199        return pool->entropy_requested - pool->entropy;
200
201    return 0;
202}
203
204/* Increase the allocation size -- not usable for an attached pool */
205static int rand_pool_grow(RAND_POOL *pool, size_t len)
206{
207    if (len > pool->alloc_len - pool->len) {
208        unsigned char *p;
209        const size_t limit = pool->max_len / 2;
210        size_t newlen = pool->alloc_len;
211
212        if (pool->attached || len > pool->max_len - pool->len) {
213            ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);
214            return 0;
215        }
216
217        do
218            newlen = newlen < limit ? newlen * 2 : pool->max_len;
219        while (len > newlen - pool->len);
220
221        if (pool->secure)
222            p = OPENSSL_secure_zalloc(newlen);
223        else
224            p = OPENSSL_zalloc(newlen);
225        if (p == NULL) {
226            ERR_raise(ERR_LIB_RAND, ERR_R_MALLOC_FAILURE);
227            return 0;
228        }
229        memcpy(p, pool->buffer, pool->len);
230        if (pool->secure)
231            OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);
232        else
233            OPENSSL_clear_free(pool->buffer, pool->alloc_len);
234        pool->buffer = p;
235        pool->alloc_len = newlen;
236    }
237    return 1;
238}
239
240/*
241 * Returns the number of bytes needed to fill the pool, assuming
242 * the input has 1 / |entropy_factor| entropy bits per data bit.
243 * In case of an error, 0 is returned.
244 */
245
246size_t ossl_rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor)
247{
248    size_t bytes_needed;
249    size_t entropy_needed = ossl_rand_pool_entropy_needed(pool);
250
251    if (entropy_factor < 1) {
252        ERR_raise(ERR_LIB_RAND, RAND_R_ARGUMENT_OUT_OF_RANGE);
253        return 0;
254    }
255
256    bytes_needed = ENTROPY_TO_BYTES(entropy_needed, entropy_factor);
257
258    if (bytes_needed > pool->max_len - pool->len) {
259        /* not enough space left */
260        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW);
261        return 0;
262    }
263
264    if (pool->len < pool->min_len &&
265        bytes_needed < pool->min_len - pool->len)
266        /* to meet the min_len requirement */
267        bytes_needed = pool->min_len - pool->len;
268
269    /*
270     * Make sure the buffer is large enough for the requested amount
271     * of data. This guarantees that existing code patterns where
272     * ossl_rand_pool_add_begin, ossl_rand_pool_add_end or ossl_rand_pool_add
273     * are used to collect entropy data without any error handling
274     * whatsoever, continue to be valid.
275     * Furthermore if the allocation here fails once, make sure that
276     * we don't fall back to a less secure or even blocking random source,
277     * as that could happen by the existing code patterns.
278     * This is not a concern for additional data, therefore that
279     * is not needed if rand_pool_grow fails in other places.
280     */
281    if (!rand_pool_grow(pool, bytes_needed)) {
282        /* persistent error for this pool */
283        pool->max_len = pool->len = 0;
284        return 0;
285    }
286
287    return bytes_needed;
288}
289
290/* Returns the remaining number of bytes available */
291size_t ossl_rand_pool_bytes_remaining(RAND_POOL *pool)
292{
293    return pool->max_len - pool->len;
294}
295
296/*
297 * Add random bytes to the random pool.
298 *
299 * It is expected that the |buffer| contains |len| bytes of
300 * random input which contains at least |entropy| bits of
301 * randomness.
302 *
303 * Returns 1 if the added amount is adequate, otherwise 0
304 */
305int ossl_rand_pool_add(RAND_POOL *pool,
306                  const unsigned char *buffer, size_t len, size_t entropy)
307{
308    if (len > pool->max_len - pool->len) {
309        ERR_raise(ERR_LIB_RAND, RAND_R_ENTROPY_INPUT_TOO_LONG);
310        return 0;
311    }
312
313    if (pool->buffer == NULL) {
314        ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);
315        return 0;
316    }
317
318    if (len > 0) {
319        /*
320         * This is to protect us from accidentally passing the buffer
321         * returned from ossl_rand_pool_add_begin.
322         * The check for alloc_len makes sure we do not compare the
323         * address of the end of the allocated memory to something
324         * different, since that comparison would have an
325         * indeterminate result.
326         */
327        if (pool->alloc_len > pool->len && pool->buffer + pool->len == buffer) {
328            ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);
329            return 0;
330        }
331        /*
332         * We have that only for cases when a pool is used to collect
333         * additional data.
334         * For entropy data, as long as the allocation request stays within
335         * the limits given by ossl_rand_pool_bytes_needed this rand_pool_grow
336         * below is guaranteed to succeed, thus no allocation happens.
337         */
338        if (!rand_pool_grow(pool, len))
339            return 0;
340        memcpy(pool->buffer + pool->len, buffer, len);
341        pool->len += len;
342        pool->entropy += entropy;
343    }
344
345    return 1;
346}
347
348/*
349 * Start to add random bytes to the random pool in-place.
350 *
351 * Reserves the next |len| bytes for adding random bytes in-place
352 * and returns a pointer to the buffer.
353 * The caller is allowed to copy up to |len| bytes into the buffer.
354 * If |len| == 0 this is considered a no-op and a NULL pointer
355 * is returned without producing an error message.
356 *
357 * After updating the buffer, ossl_rand_pool_add_end() needs to be called
358 * to finish the update operation (see next comment).
359 */
360unsigned char *ossl_rand_pool_add_begin(RAND_POOL *pool, size_t len)
361{
362    if (len == 0)
363        return NULL;
364
365    if (len > pool->max_len - pool->len) {
366        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW);
367        return NULL;
368    }
369
370    if (pool->buffer == NULL) {
371        ERR_raise(ERR_LIB_RAND, ERR_R_INTERNAL_ERROR);
372        return NULL;
373    }
374
375    /*
376     * As long as the allocation request stays within the limits given
377     * by ossl_rand_pool_bytes_needed this rand_pool_grow below is guaranteed
378     * to succeed, thus no allocation happens.
379     * We have that only for cases when a pool is used to collect
380     * additional data. Then the buffer might need to grow here,
381     * and of course the caller is responsible to check the return
382     * value of this function.
383     */
384    if (!rand_pool_grow(pool, len))
385        return NULL;
386
387    return pool->buffer + pool->len;
388}
389
390/*
391 * Finish to add random bytes to the random pool in-place.
392 *
393 * Finishes an in-place update of the random pool started by
394 * ossl_rand_pool_add_begin() (see previous comment).
395 * It is expected that |len| bytes of random input have been added
396 * to the buffer which contain at least |entropy| bits of randomness.
397 * It is allowed to add less bytes than originally reserved.
398 */
399int ossl_rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
400{
401    if (len > pool->alloc_len - pool->len) {
402        ERR_raise(ERR_LIB_RAND, RAND_R_RANDOM_POOL_OVERFLOW);
403        return 0;
404    }
405
406    if (len > 0) {
407        pool->len += len;
408        pool->entropy += entropy;
409    }
410
411    return 1;
412}
413