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sixel: prevent allocating an absurd amount of memory or writing OOB #20213

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Merged
DHowett merged 1 commit into from
May 12, 2026
+21 −5
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sixel: prevent allocating an absurd amount of memory or writing OOB #20213

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26 changes: 21 additions & 5 deletions src/terminal/adapter/SixelParser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,15 @@ std::function<bool(wchar_t)> SixelParser::DefineImage(const VTInt macroParameter
_state = States::Normal;
_parameters.clear();
return [&](const auto ch) {
_parseCommandChar(ch);
try
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@DHowett DHowett May 11, 2026

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I cannot quantify the cost of an exception handler here.

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@j4james j4james May 12, 2026

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I'm personally not too concerned about the performance, and if we get Leonard's DCS batch processing merged at some point, I expect that would mitigate the performance impact (assuming there is any).

{
_parseCommandChar(ch);
}
catch (...)
{
// Ignore all further content.
return false;
}
return true;
};
}
Expand Down Expand Up @@ -234,10 +242,18 @@ void SixelParser::_executeNextLine()
_executeCarriageReturn();
_imageLineCount++;
_maybeFlushImageBuffer();
_imageCursor.y += _sixelHeight;
_availablePixelHeight -= _sixelHeight;
_resizeImageBuffer(_sixelHeight);
_fillImageBackgroundWhenScrolled();
// If we don't have any available pixel height, that means the image has
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@DHowett DHowett May 11, 2026

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(this is getting a Co-authored-by; github is just suppressing it in the PR review window)

// extended beyond the bottom of the display and we haven't triggered a
// a scroll (because sixel display mode is enabled). In this state, there
// is no point in extending the image any further, because the additional
// content will never be seen, so we'll just be wasting memory.
if (_availablePixelHeight > 0)
{
_imageCursor.y += _sixelHeight;
_availablePixelHeight -= _sixelHeight;
_resizeImageBuffer(_sixelHeight);
_fillImageBackgroundWhenScrolled();
}
}

void SixelParser::_executeMoveToHome()
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