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Fix a potential crash in rand_unix.c

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Due to the dynamic allocation that was added to rand_pool_add_begin
this function could now return a null pointer where it was previously
guaranteed to succeed. But the return value of this function does
not need to be checked by design.

Move rand_pool_grow from rand_pool_add_begin to rand_pool_bytes_needed.
Make an allocation error persistent to avoid falling back to less secure
or blocking entropy sources.

Fixes: a6a66e4511ee ("Make rand_pool buffers more dynamic in their sizing.")

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9687)
This commit is contained in:
Bernd Edlinger 2019-09-06 21:54:13 +02:00 committed by Matt Caswell
parent e301c147a7
commit fa3eb248e2
1 changed files with 84 additions and 31 deletions
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115
crypto/rand/rand_lib.c
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@ -545,6 +545,42 @@ size_t rand_pool_entropy_needed(RAND_POOL *pool)
return 0;
}
/* Increase the allocation size -- not usable for an attached pool */
static int rand_pool_grow(RAND_POOL *pool, size_t len)
{
if (len > pool->alloc_len - pool->len) {
unsigned char *p;
const size_t limit = pool->max_len / 2;
size_t newlen = pool->alloc_len;
if (pool->attached || len > pool->max_len - pool->len) {
RANDerr(RAND_F_RAND_POOL_GROW, ERR_R_INTERNAL_ERROR);
return 0;
}
do
newlen = newlen < limit ? newlen * 2 : pool->max_len;
while (len > newlen - pool->len);
if (pool->secure)
p = OPENSSL_secure_zalloc(newlen);
else
p = OPENSSL_zalloc(newlen);
if (p == NULL) {
RANDerr(RAND_F_RAND_POOL_GROW, ERR_R_MALLOC_FAILURE);
return 0;
}
memcpy(p, pool->buffer, pool->len);
if (pool->secure)
OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);
else
OPENSSL_clear_free(pool->buffer, pool->alloc_len);
pool->buffer = p;
pool->alloc_len = newlen;
}
return 1;
}
/*
* Returns the number of bytes needed to fill the pool, assuming
* the input has 1 / |entropy_factor| entropy bits per data bit.
@ -574,6 +610,24 @@ size_t rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor)
/* to meet the min_len requirement */
bytes_needed = pool->min_len - pool->len;
/*
* Make sure the buffer is large enough for the requested amount
* of data. This guarantees that existing code patterns where
* rand_pool_add_begin, rand_pool_add_end or rand_pool_add
* are used to collect entropy data without any error handling
* whatsoever, continue to be valid.
* Furthermore if the allocation here fails once, make sure that
* we don't fall back to a less secure or even blocking random source,
* as that could happen by the existing code patterns.
* This is not a concern for additional data, therefore that
* is not needed if rand_pool_grow fails in other places.
*/
if (!rand_pool_grow(pool, bytes_needed)) {
/* persistent error for this pool */
pool->max_len = pool->len = 0;
return 0;
}
return bytes_needed;
}
@ -583,36 +637,6 @@ size_t rand_pool_bytes_remaining(RAND_POOL *pool)
return pool->max_len - pool->len;
}
static int rand_pool_grow(RAND_POOL *pool, size_t len)
{
if (len > pool->alloc_len - pool->len) {
unsigned char *p;
const size_t limit = pool->max_len / 2;
size_t newlen = pool->alloc_len;
do
newlen = newlen < limit ? newlen * 2 : pool->max_len;
while (len > newlen - pool->len);
if (pool->secure)
p = OPENSSL_secure_zalloc(newlen);
else
p = OPENSSL_zalloc(newlen);
if (p == NULL) {
RANDerr(RAND_F_RAND_POOL_GROW, ERR_R_MALLOC_FAILURE);
return 0;
}
memcpy(p, pool->buffer, pool->len);
if (pool->secure)
OPENSSL_secure_clear_free(pool->buffer, pool->alloc_len);
else
OPENSSL_clear_free(pool->buffer, pool->alloc_len);
pool->buffer = p;
pool->alloc_len = newlen;
}
return 1;
}
/*
* Add random bytes to the random pool.
*
@ -636,6 +660,25 @@ int rand_pool_add(RAND_POOL *pool,
}
if (len > 0) {
/*
* This is to protect us from accidentally passing the buffer
* returned from rand_pool_add_begin.
* The check for alloc_len makes sure we do not compare the
* address of the end of the allocated memory to something
* different, since that comparison would have an
* indeterminate result.
*/
if (pool->alloc_len > pool->len && pool->buffer + pool->len == buffer) {
RANDerr(RAND_F_RAND_POOL_ADD, ERR_R_INTERNAL_ERROR);
return 0;
}
/*
* We have that only for cases when a pool is used to collect
* additional data.
* For entropy data, as long as the allocation request stays within
* the limits given by rand_pool_bytes_needed this rand_pool_grow
* below is guaranteed to succeed, thus no allocation happens.
*/
if (!rand_pool_grow(pool, len))
return 0;
memcpy(pool->buffer + pool->len, buffer, len);
@ -673,8 +716,18 @@ unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len)
return NULL;
}
/*
* As long as the allocation request stays within the limits given
* by rand_pool_bytes_needed this rand_pool_grow below is guaranteed
* to succeed, thus no allocation happens.
* We have that only for cases when a pool is used to collect
* additional data. Then the buffer might need to grow here,
* and of course the caller is responsible to check the return
* value of this function.
*/
if (!rand_pool_grow(pool, len))
return NULL;
return pool->buffer + pool->len;
}
@ -689,7 +742,7 @@ unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len)
*/
int rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
{
if (len > pool->max_len - pool->len) {
if (len > pool->alloc_len - pool->len) {
RANDerr(RAND_F_RAND_POOL_ADD_END, RAND_R_RANDOM_POOL_OVERFLOW);
return 0;
}