crypto: Add ssh_crypto_free().

The intention is that this releases memory allocated by the crypto
library, for functions like bignum_bn2hex() and bignum_bn2dec().
Consequently, ssh_gcry_bn2dec and ssh_mbedcry_bn2num should use
gcry_malloc() and mbedtls_calloc() respectively to allocate
memory since it will/should be released by ssh_crypto_free() so
that the internal APIs are consistent between crypto libraries.

Signed-off-by: Simon Josefsson <simon@josefsson.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

src/bignum.c

@@ -88,11 +88,5 @@ void ssh_print_bignum(const char *name, const_bignum num)
     }
     SSH_LOG(SSH_LOG_DEBUG, "%s value: %s", name,
             (hex == NULL) ? "(null)" : (char *)hex);
-#ifdef HAVE_LIBGCRYPT
-    SAFE_FREE(hex);
-#elif defined HAVE_LIBCRYPTO
-    OPENSSL_free(hex);
-#elif defined HAVE_LIBMBEDCRYPTO
-    SAFE_FREE(hex);
-#endif
+    ssh_crypto_free(hex);
 }

src/gcrypt_missing.c

@@ -55,7 +55,7 @@ char *ssh_gcry_bn2dec(bignum bn) {
   size = gcry_mpi_get_nbits(bn) * 3;
   rsize = size / 10 + size / 1000 + 2;
 
-  ret = malloc(rsize + 1);
+  ret = gcry_malloc(rsize + 1);
   if (ret == NULL) {
     return NULL;
   }

src/mbedcrypto_missing.c

@@ -56,7 +56,7 @@ char *ssh_mbedcry_bn2num(const_bignum num, int radix)
         return NULL;
     }
 
-    buf = malloc(olen);
+    buf = mbedtls_calloc(1, olen);
     if (buf == NULL) {
         return NULL;
     }