CNA-BUG-251: BoundingSphere(Vector3 center, float radius) accepts a negative radius, where XNA 4.0 throws ArgumentException

CNA snapshot 009d40f5  ·  Known Issues › Current bugs  ·  source links pinned to 009d40f5

CNA's BoundingSphere(Vector3, float) constructor stores any radius, while XNA 4.0's throws ArgumentException for radius < 0, so a negative radius is silently accepted.

Identifier

CNA-BUG-251

Category

Bug

Subsystem

Math & geometry

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Severity

Low (a triage suggestion, not a project priority)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

CNA::BoundingSphere::BoundingSphere(Vector3 center, float radius) (Microsoft::Xna::Framework::BoundingSphere)

Expected behaviour

XNA 4.0's constructor (read from the decompiled genuine Microsoft.Xna.Framework assembly, BoundingSphere.cs) is if (radius < 0f) throw new ArgumentException(FrameworkResources.NegativeRadius); followed by the two assignments, so a sphere with a negative radius cannot be constructed through it.

Actual behaviour at TARGET

BoundingSphere::BoundingSphere(Vector3, float) in BoundingSphere.cpp is a bare initializer list, Center(center), Radius(radius): it validates nothing, so a caller that passes a negative radius gets a sphere with a negative Radius instead of the exception. Sibling math code already throws sharp-runtime exceptions for invalid arguments (System::ArgumentException in BoundingBox.cpp), so the mechanism exists.

Source locations

• modules/math/src/BoundingSphere.cpp — BoundingSphere::BoundingSphere(Vector3, float): an unvalidated initializer list
• modules/math/include/Microsoft/Xna/Framework/BoundingSphere.hpp — the constructor declaration
• modules/math/tests/Microsoft/Xna/Framework/BoundingSphereTests.cpp — ConstructorStoresCenterAndRadius: positive radius only

Evidence

Checked by reading at 009d40f5; nothing was built or executed for this entry. XNA's guard was read in the decompiled reference (xna4-decomp). Found by the independent adversarial review of the math entries, not by an earlier audit; no published entry covers it (CNA-BUG-070 is about Contains, CNA-BUG-025 about the PlaneIntersectionType Doxygen). The other construction paths of the type (default constructor, the CreateFrom* helpers, Transform) were not examined for the same invariant.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

BoundingSphereTests.cpp constructs spheres with a positive radius (ConstructorStoresCenterAndRadius); no case passes a negative one.

Regression test

A test that BoundingSphere(Vector3::Zero, -1.0f) throws an ArgumentException-family exception, and that a zero radius still constructs.

Blast radius

Code that builds a BoundingSphere from a computed radius, and XNA code that relies on the constructor's ArgumentException to reject bad input. Correct programs that only pass non-negative radii are unaffected.

Workaround

Validate the radius (radius >= 0) before constructing.