contrib/apr: Rip out bogus [CS]PRNG implementation
This construction used some relatively slow design involving SHA2; even if it were fed real entropy (unclear; external to the design), it did not handle fork in a safe way, and it was difficult to audit for correctness. So just rip it out and use the very simple and known-correct arc4random(3) interface in its place.
This commit is contained in:
Conrad Meyer
parent
295e4149b0
commit
53345534c8
@ -13,285 +13,51 @@
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* See the paper "On Randomness" by Ben Laurie for an explanation of this PRNG.
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* http://www.apache-ssl.org/randomness.pdf
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* XXX: Is there a formal proof of this PRNG? Couldn't we use the more popular
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* Mersenne Twister PRNG (and BSD licensed)?
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*/
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#include "apr.h"
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#include "apr_pools.h"
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#include "apr_random.h"
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#include "apr_thread_proc.h"
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#include <assert.h>
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#ifdef min
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#undef min
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#endif
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#define min(a,b) ((a) < (b) ? (a) : (b))
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#define APR_RANDOM_DEFAULT_POOLS 32
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#define APR_RANDOM_DEFAULT_REHASH_SIZE 1024
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#define APR_RANDOM_DEFAULT_RESEED_SIZE 32
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#define APR_RANDOM_DEFAULT_HASH_SECRET_SIZE 32
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#define APR_RANDOM_DEFAULT_G_FOR_INSECURE 32
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#define APR_RANDOM_DEFAULT_G_FOR_SECURE 320
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typedef struct apr_random_pool_t {
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unsigned char *pool;
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unsigned int bytes;
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unsigned int pool_size;
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} apr_random_pool_t;
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#define hash_init(h) (h)->init(h)
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#define hash_add(h,b,n) (h)->add(h,b,n)
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#define hash_finish(h,r) (h)->finish(h,r)
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#define hash(h,r,b,n) hash_init(h),hash_add(h,b,n),hash_finish(h,r)
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#define crypt_setkey(c,k) (c)->set_key((c)->data,k)
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#define crypt_crypt(c,out,in) (c)->crypt((c)->date,out,in)
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struct apr_random_t {
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apr_pool_t *apr_pool;
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apr_crypto_hash_t *pool_hash;
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unsigned int npools;
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apr_random_pool_t *pools;
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unsigned int next_pool;
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unsigned int generation;
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apr_size_t rehash_size;
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apr_size_t reseed_size;
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apr_crypto_hash_t *key_hash;
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#define K_size(g) ((g)->key_hash->size)
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apr_crypto_hash_t *prng_hash;
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#define B_size(g) ((g)->prng_hash->size)
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unsigned char *H;
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unsigned char *H_waiting;
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#define H_size(g) (B_size(g)+K_size(g))
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#define H_current(g) (((g)->insecure_started && !(g)->secure_started) \
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? (g)->H_waiting : (g)->H)
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unsigned char *randomness;
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apr_size_t random_bytes;
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unsigned int g_for_insecure;
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unsigned int g_for_secure;
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unsigned int secure_base;
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unsigned int insecure_started:1;
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unsigned int secure_started:1;
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apr_random_t *next;
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};
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static apr_random_t *all_random;
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static apr_status_t random_cleanup(void *data)
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{
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apr_random_t *remove_this = data,
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*cur = all_random,
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**prev_ptr = &all_random;
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while (cur) {
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if (cur == remove_this) {
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*prev_ptr = cur->next;
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break;
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}
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prev_ptr = &cur->next;
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cur = cur->next;
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}
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return APR_SUCCESS;
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}
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#include <stdlib.h>
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APR_DECLARE(void) apr_random_init(apr_random_t *g,apr_pool_t *p,
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apr_crypto_hash_t *pool_hash,
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apr_crypto_hash_t *key_hash,
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apr_crypto_hash_t *prng_hash)
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{
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unsigned int n;
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g->apr_pool = p;
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g->pool_hash = pool_hash;
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g->key_hash = key_hash;
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g->prng_hash = prng_hash;
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g->npools = APR_RANDOM_DEFAULT_POOLS;
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g->pools = apr_palloc(p,g->npools*sizeof *g->pools);
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for (n = 0; n < g->npools; ++n) {
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g->pools[n].bytes = g->pools[n].pool_size = 0;
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g->pools[n].pool = NULL;
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}
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g->next_pool = 0;
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g->generation = 0;
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g->rehash_size = APR_RANDOM_DEFAULT_REHASH_SIZE;
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/* Ensure that the rehash size is twice the size of the pool hasher */
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g->rehash_size = ((g->rehash_size+2*g->pool_hash->size-1)/g->pool_hash->size
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/2)*g->pool_hash->size*2;
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g->reseed_size = APR_RANDOM_DEFAULT_RESEED_SIZE;
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g->H = apr_pcalloc(p,H_size(g));
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g->H_waiting = apr_pcalloc(p,H_size(g));
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g->randomness = apr_palloc(p,B_size(g));
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g->random_bytes = 0;
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g->g_for_insecure = APR_RANDOM_DEFAULT_G_FOR_INSECURE;
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g->secure_base = 0;
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g->g_for_secure = APR_RANDOM_DEFAULT_G_FOR_SECURE;
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g->secure_started = g->insecure_started = 0;
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g->next = all_random;
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all_random = g;
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apr_pool_cleanup_register(p, g, random_cleanup, apr_pool_cleanup_null);
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}
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static void mix_pid(apr_random_t *g,unsigned char *H,pid_t pid)
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{
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hash_init(g->key_hash);
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hash_add(g->key_hash,H,H_size(g));
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hash_add(g->key_hash,&pid,sizeof pid);
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hash_finish(g->key_hash,H);
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}
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static void mixer(apr_random_t *g,pid_t pid)
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{
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unsigned char *H = H_current(g);
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/* mix the PID into the current H */
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mix_pid(g,H,pid);
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/* if we are in waiting, then also mix into main H */
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if (H != g->H)
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mix_pid(g,g->H,pid);
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/* change order of pool mixing for good measure - note that going
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backwards is much better than going forwards */
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--g->generation;
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/* blow away any lingering randomness */
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g->random_bytes = 0;
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(void)g;
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(void)p;
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(void)pool_hash;
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(void)key_hash;
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(void)prng_hash;
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}
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APR_DECLARE(void) apr_random_after_fork(apr_proc_t *proc)
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{
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apr_random_t *r;
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for (r = all_random; r; r = r->next)
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/*
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* XXX Note: the pid does not provide sufficient entropy to
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* actually call this secure. See Ben's paper referenced at
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* the top of this file.
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*/
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mixer(r,proc->pid);
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(void)proc;
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}
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APR_DECLARE(apr_random_t *) apr_random_standard_new(apr_pool_t *p)
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{
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apr_random_t *r = apr_palloc(p,sizeof *r);
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apr_random_init(r,p,apr_crypto_sha256_new(p),apr_crypto_sha256_new(p),
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apr_crypto_sha256_new(p));
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return r;
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}
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static void rekey(apr_random_t *g)
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{
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unsigned int n;
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unsigned char *H = H_current(g);
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hash_init(g->key_hash);
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hash_add(g->key_hash,H,H_size(g));
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for (n = 0 ; n < g->npools && (n == 0 || g->generation&(1 << (n-1)))
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; ++n) {
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hash_add(g->key_hash,g->pools[n].pool,g->pools[n].bytes);
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g->pools[n].bytes = 0;
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}
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hash_finish(g->key_hash,H+B_size(g));
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++g->generation;
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if (!g->insecure_started && g->generation > g->g_for_insecure) {
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g->insecure_started = 1;
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if (!g->secure_started) {
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memcpy(g->H_waiting,g->H,H_size(g));
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g->secure_base = g->generation;
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}
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}
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if (!g->secure_started && g->generation > g->secure_base+g->g_for_secure) {
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g->secure_started = 1;
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memcpy(g->H,g->H_waiting,H_size(g));
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}
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/* apr_random_t is an opaque struct type. */
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return (void *)0x1;
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}
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APR_DECLARE(void) apr_random_add_entropy(apr_random_t *g,const void *entropy_,
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apr_size_t bytes)
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{
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unsigned int n;
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const unsigned char *entropy = entropy_;
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for (n = 0; n < bytes; ++n) {
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apr_random_pool_t *p = &g->pools[g->next_pool];
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if (++g->next_pool == g->npools)
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g->next_pool = 0;
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if (p->pool_size < p->bytes+1) {
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unsigned char *np = apr_palloc(g->apr_pool,(p->bytes+1)*2);
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memcpy(np,p->pool,p->bytes);
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p->pool = np;
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p->pool_size = (p->bytes+1)*2;
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}
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p->pool[p->bytes++] = entropy[n];
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if (p->bytes == g->rehash_size) {
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apr_size_t r;
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for (r = 0; r < p->bytes/2; r+=g->pool_hash->size)
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hash(g->pool_hash,p->pool+r,p->pool+r*2,g->pool_hash->size*2);
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p->bytes/=2;
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}
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assert(p->bytes < g->rehash_size);
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}
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if (g->pools[0].bytes >= g->reseed_size)
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rekey(g);
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}
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/* This will give g->B_size bytes of randomness */
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static void apr_random_block(apr_random_t *g,unsigned char *random)
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{
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/* FIXME: in principle, these are different hashes */
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hash(g->prng_hash,g->H,g->H,H_size(g));
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hash(g->prng_hash,random,g->H,B_size(g));
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}
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static void apr_random_bytes(apr_random_t *g,unsigned char *random,
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apr_size_t bytes)
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{
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apr_size_t n;
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for (n = 0; n < bytes; ) {
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apr_size_t l;
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if (g->random_bytes == 0) {
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apr_random_block(g,g->randomness);
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g->random_bytes = B_size(g);
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}
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l = min(bytes-n,g->random_bytes);
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memcpy(&random[n],g->randomness+B_size(g)-g->random_bytes,l);
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g->random_bytes-=l;
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n+=l;
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}
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(void)g;
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(void)entropy_;
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(void)bytes;
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}
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APR_DECLARE(apr_status_t) apr_random_secure_bytes(apr_random_t *g,
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void *random,
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apr_size_t bytes)
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{
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if (!g->secure_started)
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return APR_ENOTENOUGHENTROPY;
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apr_random_bytes(g,random,bytes);
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(void)g;
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arc4random_buf(random, bytes);
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return APR_SUCCESS;
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}
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@ -299,28 +65,24 @@ APR_DECLARE(apr_status_t) apr_random_insecure_bytes(apr_random_t *g,
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void *random,
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apr_size_t bytes)
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{
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if (!g->insecure_started)
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return APR_ENOTENOUGHENTROPY;
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apr_random_bytes(g,random,bytes);
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(void)g;
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arc4random_buf(random, bytes);
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return APR_SUCCESS;
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}
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APR_DECLARE(void) apr_random_barrier(apr_random_t *g)
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{
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g->secure_started = 0;
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g->secure_base = g->generation;
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(void)g;
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}
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APR_DECLARE(apr_status_t) apr_random_secure_ready(apr_random_t *r)
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{
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if (!r->secure_started)
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return APR_ENOTENOUGHENTROPY;
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(void)r;
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return APR_SUCCESS;
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}
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APR_DECLARE(apr_status_t) apr_random_insecure_ready(apr_random_t *r)
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{
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if (!r->insecure_started)
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return APR_ENOTENOUGHENTROPY;
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(void)r;
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return APR_SUCCESS;
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}
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