Fix integer overflow in ImmutableArray range validation

[prozolic]

#124043
Prevent OutOfMemoryException by detecting integer overflow when validating start + length parameters. Previously, when start=1 and length=int.MaxValue, the addition would overflow to a negative value, incorrectly passing validation and causing OutOfMemoryException during array allocation.

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[Copilot]

Pull request overview

This pull request fixes an integer overflow vulnerability in ImmutableArray range validation that could cause OutOfMemoryException. When start=1 and length=int.MaxValue, the addition start + length would overflow to a negative value, incorrectly passing validation and causing OutOfMemoryException during array allocation.

Changes:

• Updated range validation in 4 methods to use unsigned arithmetic for overflow detection
• Added comprehensive test coverage for the overflow scenario in all 4 affected methods

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray.cs	Fixed integer overflow in range validation by casting start + length to uint for comparison in 4 methods: Create(T[], int, int), Create(ImmutableArray, int, int), CreateRange with selector, and CreateRange with selector and argument
src/libraries/System.Collections.Immutable/tests/ImmutableArrayTest.cs	Added test cases for the overflow scenario (start=1, length=int.MaxValue) in 4 test methods corresponding to the fixed methods, each properly guarded with array.Length > 0 check

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.