RFR: 8346094: Harden X509CertImpl.getExtensionValue for NPE cases

[Weijun Wang]

On Mon, 27 Jan 2025 12:39:45 GMT, Konanki Sreenath <duke at openjdk.org> wrote:

> Earlier code will trigger NPE if the certificate does not contain the extensions or if the requested extensions does not exist. The better approach for hardening **getExtensionValue** here is to to check for NULL explicitly before calling **getExtensionValue()** and avoding try-catch block which ensures the readability and maintainability.
> 
> After scanning in multiple places where invokng getExtensions on the X509CertInfo reference, the check for NULL is added in the **getKeyUsage()** as well while calling before **getExtensionValue()**
> 
> The associated tests are written and added in test class **CertificateExtensions**. Which will ensure to validate the 
> **getExtensionValue()** and **getKeyUsage()** methods in **X509CertImpl** class.

I'm wondering how necessary this fix is. These are internal classes, only called inside JDK, where some pre-conditions are always met. Unless someone explicitly calls `x509Certimpl.getInfo().setExtensions(null)` (as done in the test), it seems like both the `info` and `extensions` fields should never be null.

If you’re concerned about misuse of these methods leading to potential future issues, consider adding comments to clarify their expected usage. You could also include `assert` statements or `Objects.requireNonNull` calls to enforce these preconditions.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/23315#issuecomment-2640005099