Limit the execution time of RSA public key check

Fixes CVE-2023-6237

If a large and incorrect RSA public key is checked with
EVP_PKEY_public_check() the computation could take very long time
due to no limit being applied to the RSA public key size and
unnecessarily high number of Miller-Rabin algorithm rounds
used for non-primality check of the modulus.

Now the keys larger than 16384 bits (OPENSSL_RSA_MAX_MODULUS_BITS)
will fail the check with RSA_R_MODULUS_TOO_LARGE error reason.
Also the number of Miller-Rabin rounds was set to 5.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23243)

crypto/rsa/rsa_sp800_56b_check.c

@@ -289,6 +289,11 @@ int ossl_rsa_sp800_56b_check_public(const RSA *rsa)
         return 0;
 
     nbits = BN_num_bits(rsa->n);
+    if (nbits > OPENSSL_RSA_MAX_MODULUS_BITS) {
+        ERR_raise(ERR_LIB_RSA, RSA_R_MODULUS_TOO_LARGE);
+        return 0;
+    }
+
 #ifdef FIPS_MODULE
     /*
      * (Step a): modulus must be 2048 or 3072 (caveat from SP800-56Br1)
@@ -324,7 +329,8 @@ int ossl_rsa_sp800_56b_check_public(const RSA *rsa)
         goto err;
     }
 
-    ret = ossl_bn_miller_rabin_is_prime(rsa->n, 0, ctx, NULL, 1, &status);
+    /* Highest number of MR rounds from FIPS 186-5 Section B.3 Table B.1 */
+    ret = ossl_bn_miller_rabin_is_prime(rsa->n, 5, ctx, NULL, 1, &status);
 #ifdef FIPS_MODULE
     if (ret != 1 || status != BN_PRIMETEST_COMPOSITE_NOT_POWER_OF_PRIME) {
 #else

test/recipes/91-test_pkey_check.t

@@ -70,7 +70,7 @@ push(@positive_tests, (
     "dhpkey.pem"
     )) unless disabled("dh");
 
-my @negative_pubtests = ();
+my @negative_pubtests = ("rsapub_17k.pem");  # Too big RSA public key
 
 push(@negative_pubtests, (
     "dsapub_noparam.der"

test/recipes/91-test_pkey_check_data/rsapub_17k.pem

@@ -0,0 +1,48 @@
+-----BEGIN PUBLIC KEY-----
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+-----END PUBLIC KEY-----