DRBG: fix reseeding via RAND_add()/RAND_seed() with large input

In pull request #4328 the seeding of the DRBG via RAND_add()/RAND_seed()
was implemented by buffering the data in a random pool where it is
picked up later by the rand_drbg_get_entropy() callback. This buffer
was limited to the size of 4096 bytes.

When a larger input was added via RAND_add() or RAND_seed() to the DRBG,
the reseeding failed, but the error returned by the DRBG was ignored
by the two calling functions, which both don't return an error code.
As a consequence, the data provided by the application was effectively
ignored.

This commit fixes the problem by a more efficient implementation which
does not copy the data in memory and by raising the buffer the size limit
to INT32_MAX (2 gigabytes). This is less than the NIST limit of 2^35 bits
but it was chosen intentionally to avoid platform dependent problems
like integer sizes and/or signed/unsigned conversion.

Additionally, the DRBG is now less permissive on errors: In addition to
pushing a message to the openssl error stack, it enters the error state,
which forces a reinstantiation on next call.

Thanks go to Dr. Falko Strenzke for reporting this issue to the
openssl-security mailing list. After internal discussion the issue
has been categorized as not being security relevant, because the DRBG
reseeds automatically and is fully functional even without additional
randomness provided by the application.

Fixes #7381

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/7382)

1 files changed, 2 insertions, 0 deletions

diff --git a/crypto/include/internal/rand_int.h b/crypto/include/internal/rand_int.h
index d91ee4c934..3c966ab96e 100644
--- a/crypto/include/internal/rand_int.h
+++ b/crypto/include/internal/rand_int.h
@@ -53,6 +53,8 @@ void rand_drbg_cleanup_additional_data(unsigned char *out, size_t outlen);
  * RAND_POOL functions
  */
 RAND_POOL *rand_pool_new(int entropy_requested, size_t min_len, size_t max_len);
+RAND_POOL *rand_pool_attach(const unsigned char *buffer, size_t len,
+                            size_t entropy);
 void rand_pool_free(RAND_POOL *pool);
 
 const unsigned char *rand_pool_buffer(RAND_POOL *pool);