openssl_get_publickey(): With public key PEM, results in error:0480006C:PEM routines::no start line

[famoser]

Description

The following code:

<?php
$publicKeyPem = <<EOD
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvYH14fT4DPgyffkDOrHt
x0q+rxclB48h2ykgbR3QyDG2d7hMSXjtqEseO/iR1FdAv7UevIKyHFbHpJilOIwo
mEqQNxUQCWdZsWhv7ZVfG8UUgki7LKMGPruJM97vteBS101hSCaCQz+zTyVyP8Uy
nqx5zlPmcBUA92gAFfSCa+tm/lR2BY5g/20mZX/lMY0xXV1iLhfdK6RgJYXX2SdH
YR/01IgmjgTfIp7gX+xixDgGZuZY++jo8C52udFkCf5vxyG4Ed57vRfCLFOPfeY4
r3i0Jiply65zSo8y/6KxudRtmGOfV2qb2EsMTW9PaLs3+rnhhiYBM/nR4V5ux6u6
DwIDAQAB
-----END PUBLIC KEY-----
EOD;
openssl_get_publickey($publicKeyPem);
var_dump(openssl_error_string());

Resulted in this output:

string(54) "error:0906D06C:PEM routines:PEM_read_bio:no start line"

But I expected this output instead:

bool(false)

Note that openssl_get_publickey succeeded; the error is there nonetheless. More elaborate test cases here: https://github.com/famoser/polyas-verification/blob/a28f16437ab695548b3cb301258f87badf7aee69/tests/Utils/OpenSSLBugs.php

Analysis

The error happens when the PEM contains a public key, as it will be first tried to be parsed as a certificate (see here). The parsing as a certificate fails, which then leads to a corresponding error tracked by PHP with the next call to php_openssl_store_errors().

As PHP handles the case where the certificate cannot be parsed, consequentially this error should never reach the user. Else the user-code would need to ignore this error somehow, which requires knowledge of implementation details when this is safe to do, and when not.

Solution

I see two ways how to fix the issue.

Prevent error being stored

The error should never reach PHP's OPENSSL_G(errors) buffer. Prevent php_openssl_x509_from_str to store the errors, and discard them in php_openssl_pkey_from_zval.

Pseudo-code:

/* {{{ php_openssl_discard_errors */
void php_openssl_discard_errors(void)
{
	int error_code;
	while ((error_code = ERR_get_error()));
}
/* }}} */

static EVP_PKEY *php_openssl_pkey_from_zval(
		zval *val, int public_key, char *passphrase, size_t passphrase_len, uint32_t arg_num)
{
  // ...
  php_openssl_store_errors();
  cert = php_openssl_x509_from_str(Z_STR_P(val), arg_num, false, NULL, true);
  if (cert) {
    free_cert = 1;
  } else {
    php_openssl_discard_errors();
    // ...
  }
}

static X509 *php_openssl_x509_from_str(
		zend_string *cert_str, uint32_t arg_num, bool is_from_array, const char *option_name, const int store_errors) {
  // ... (4 times)
  if (store_errors) {
    php_openssl_store_errors();
  }
  // ...
}

Mark & Revert error

Similar to how openSSL error buffer works, introduce an option to mark the buffer at a specific state, and allow to revert to this state.

Pseudo-code:

/* {{{ php_openssl_errors_set_mark */
void php_openssl_errors_set_mark(void) {
	if (!OPENSSL_G(errors)) {
		return;
	}

	OPENSSL_G(errors_mark) = pecalloc(1, sizeof(struct php_openssl_errors), 1);
	memcpy(OPENSSL_G(errors), OPENSSL_G(errors_mark), sizeof(struct php_openssl_errors));
}
/* }}} */

/* {{{ php_openssl_errors_restore_mark */
void php_openssl_errors_restore_mark(void) {
	struct php_openssl_errors *errors;

	if (!OPENSSL_G(errors)) {
		return;
	}

	if (!OPENSSL_G(errors_mark)) {
		errors = OPENSSL_G(errors);
		errors->top = 0;
		errors->bottom = 0;
	} else {
		memcpy(OPENSSL_G(errors_mark), OPENSSL_G(errors), sizeof(struct php_openssl_errors));
	}
}
/* }}} */

static EVP_PKEY *php_openssl_pkey_from_zval(
		zval *val, int public_key, char *passphrase, size_t passphrase_len, uint32_t arg_num)
{
  // ...
  php_openssl_errors_set_mark();
  cert = php_openssl_x509_from_str(Z_STR_P(val), arg_num, false, NULL);

  if (cert) {
    free_cert = 1;
  } else {
    php_openssl_errors_restore_mark();
    // ...
  }
}

I'll create a PR shortly for this second version. I feel it is less intrusive and simpler to understand. Let me know if you have a different option on this, and I'll update the PR.

PHP Version

PHP 8.0.28, PHP 8.1.17, PHP 8.2.4

Operating System

No response