[release/8.0-staging] Fix thread safety in SafeEvpPKeyHandle.DuplicateHandle

[bartonjs]

Manual backport of #124485 to release/8.0-staging

Customer Impact

• Customer reported
• Found internally

Parallel calls to Dispose and DuplicateHandle on SafeEvpPKeyHandle can result in a state where the native handle gets up-ref'd, but the SafeHandle returned from DuplicateHandle is tracking the zero-valued handle, so the underlying free never gets called (and interacting with the returned SafeHandle doesn't do what you want, either).

Regression

• Yes
• No

Testing

A dedicated test is added with this change.

Risk

Low. DangerousAddRef/DangerousRelease is a standard treatment for SafeHandle atomicity.

[Copilot]

Pull request overview

This PR backports a thread safety fix for SafeEvpPKeyHandle.DuplicateHandle from the main branch to release/8.0-staging. The issue occurs when DuplicateHandle and Dispose are called concurrently on the same handle, potentially resulting in a duplicated handle that tracks IntPtr.Zero instead of the actual native handle, causing memory leaks and invalid handle operations.

Changes:

• Wraps the critical section of DuplicateHandle with DangerousAddRef/DangerousRelease to prevent concurrent Dispose from zeroing the handle field during duplication
• Adds a regression test that verifies concurrent DuplicateHandle and Dispose calls don't produce invalid handles

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/SafeEvpPKeyHandle.OpenSsl.cs	Fixes thread safety race condition in DuplicateHandle by using DangerousAddRef/DangerousRelease to prevent concurrent disposal
src/libraries/System.Security.Cryptography.OpenSsl/tests/SafeEvpPKeyHandleTests.cs	Adds regression test that verifies concurrent DuplicateHandle and Dispose operations don't produce invalid handles

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