Possible out-of-bounds array access in `WindowGasPropertiesAtTemp()` inner loop (`j <= NMix should be j < NMix`)

[dareumnam]

Issue overview

• In WindowManager.cc, WindowGasPropertiesAtTemp(), the inner loop for calculating the viscosity of a gas mixture has an off-by-one error:

for (int i = 0; i < NMix; ++i) {
    for (int j = 0; j <= NMix; ++j) {  //                     ← bug here
        auto const &wmgasJ = wm->gaps[iGap].gases[j];
        // ...
    }
}

• The valid indices for gaps[iGap].gases are 0 through NMix - 1. However, the condition j <= NMix allows j to reach NMix on the last iteration, causing gases[NMix] to be accessed, which is one element past the end of the array. This seems an out-of-bounds memory access.

Operating System (Multiple choices)

Windows

Operating System Version

11

Version of EnergyPlus

26.01

Unmethours link or helpdesk ticket number

N/A

Defect file

No response

[rraustad]

Your assessment is spot on. There must not be an example file or unit test that uses 5 gases otherwise this loop would crash in a debug build.

int constexpr maxMixGases = 5;
std::array<Gas, maxMixGases> gases = {Gas()};  <- indexed 0 to 4

    NMix = wm->gaps[iGap].numGases;

[dareumnam]

@rraustad Thanks so much for confirming. I'll create a PR to fix this, including a unit test to cover this loop.