Prevent stack-buffer-overflow with address sanitizer

srtp/crypto/cipher/aes_gcm_ossl.c

 /*
  * aes_gcm_ossl.c
  *
  * AES Galois Counter Mode
  *
  * John A. Foley
  * Cisco Systems, Inc.
  *
  */
 
@@ skipping 249 matching lines @@
  */
 err_status_t aes_gcm_openssl_set_aad (aes_gcm_ctx_t *c, unsigned char *aad, 
                                       unsigned int aad_len)
 {
     int rv;
 
     /*
      * Set dummy tag, OpenSSL requires the Tag to be set before
      * processing AAD
      */
-    EVP_CIPHER_CTX_ctrl(&c->ctx, EVP_CTRL_GCM_SET_TAG, c->tag_len, aad);
+    unsigned char dummy_tag[GCM_AUTH_TAG_LEN];
+    memset(dummy_tag, 0x0, GCM_AUTH_TAG_LEN);
+    EVP_CIPHER_CTX_ctrl(&c->ctx, EVP_CTRL_GCM_SET_TAG, c->tag_len, &dummy_tag);

[tommi, 2016/07/26 08:47:14]

does sizeof(dummy_tag) have to match c->tag_len?

[joachim, 2016/07/26 09:08:38]

Yes, but it has to be between 1 and 16 bytes (see
https://cs.chromium.org/chromium/src/third_party/boringssl/src/crypto/cipher/...),
so always passing a buffer with "GCM_AUTH_TAG_LEN" (i.e. 16) bytes will work in
any case.

[tommi, 2016/07/26 09:45:09]

Acknowledged.

 
     rv = EVP_Cipher(&c->ctx, NULL, aad, aad_len);
     if (rv != aad_len) {
         return (err_status_algo_fail);
     } else {
         return (err_status_ok);
     }
 }
 
 /*
@@ skipping 280 matching lines @@
     (cipher_decrypt_func_t)     aes_gcm_openssl_decrypt,
     (cipher_set_iv_func_t)      aes_gcm_openssl_set_iv,
     (cipher_get_tag_func_t)     aes_gcm_openssl_get_tag,
     (char*)                     aes_gcm_256_openssl_description,
     (int)                       0,         /* instance count */
     (cipher_test_case_t*)       &aes_gcm_test_case_1,
     (debug_module_t*)           &mod_aes_gcm,
     (cipher_type_id_t)          AES_256_GCM
 };