#949 potential free on unitialized pointers in error case in generate_key

[Dirk Mueller]

There is a potential use of free on unitialized variables in privoxy-4.2.0-stable/openssl.c for openssl versions older than 3.0.

in the function generate_key(struct client_state csp, char *key_buf),
Under OpenSSL versions older than 3.0.0 (i.e., when OPENSSL_VERSION_NUMBER < 0x30000000L), the function declares exp, rsa, and ec_key on the stack without initializing them to NULL:

#if (OPENSSL_VERSION_NUMBER < 0x30000000L)
   BIGNUM *exp;
   RSA *rsa;
   EC_KEY *ec_key;
#endif

If key = EVP_PKEY_new(); fails, the code jumps directly to the cleanup section:

   key = EVP_PKEY_new();
   if (key == NULL)
   {
      log_ssl_errors(LOG_LEVEL_ERROR, "RSA/EC key memory allocation failure.");
      ret = -1;
      goto exit;
   }

At the exit label, the uninitialized stack variables are checked and passed to freeing functions:

exit:
   /*

    * Freeing used variables
    */
#if (OPENSSL_VERSION_NUMBER < 0x30000000L)
   if (csp->config->elliptic_curve_keys)
   {
      if (ec_key)
      {
         EC_KEY_free(ec_key);
      }
   }
   else
   {
      if (exp)
      {
         BN_free(exp);
      }
      if (rsa)
      {
         RSA_free(rsa);
      }
   }
#endif

Because ec_key, exp, and rsa contain garbage from the stack, calling EC_KEY_free(), BN_free(), or RSA_free() with these arbitrary addresses results in undefined behavior, memory corruption, and potential crashes.

[Fabian Keil]

Thanks a lot for the report.

Fixed in 0783764ef5604.