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[PR #8309] Fix out-of-bounds exceptions in Set...{Buffer,Screen}Size #27161

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opened 2026-01-31 09:20:21 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:20:21 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/8309

State: closed
Merged: Yes

This fixes a number of exceptions that can cause conhost to crash when
the buffer is resized in such a way that the viewport or cursor position
end up out of bounds.

References

Technically this is a fix for issue #256, although that has been closed
as "needs-repro".

PR Checklist

  • CLA signed.
  • Tests added/passed
  • Documentation updated.
  • Schema updated.
  • I've discussed this with core contributors already. Issue number where discussion took place: #1976

Detailed Description of the Pull Request / Additional comments

The main fix was to add checks in the SetConsoleScreenBufferSizeImpl
and SetConsoleScreenBufferInfoExImpl methods, to make sure the
viewport doesn't extend past the bottom or right of the buffer after a
resize. If it has overflowed, we move the viewport back up or left until
it's back within the buffer boundaries. We also check if the cursor
position has ended up out of bounds, and if so, clamp it back inside the
buffer.

The SCREEN_INFORMATION::SetViewport was also a source of viewport
overflow problems, because it was mistakenly using inclusive coordinates
in its range checks, which resulted in them being off by one. That has
now been corrected to use exclusive coordinates.

Finally, the IsCursorDoubleWidth method was incorrectly marked as
noexcept, which was preventing its exceptions from being caught.
Ideally it shouldn't be throwing exceptions at all any more, but I've
removed the noexcept specifier, so if it does throw an exception,
it'll at least have more chance of recovering without a crash.

Validation Steps Performed

I put together a few test cases (based on the reports in issues #276 and
#1976) which consistently caused conhost to crash, or to generate an
exception visible in the debug output. With this PR applied, those test
cases are no longer crashing or triggering exceptions.

Closes #1976

**Original Pull Request:** https://github.com/microsoft/terminal/pull/8309 **State:** closed **Merged:** Yes --- This fixes a number of exceptions that can cause conhost to crash when the buffer is resized in such a way that the viewport or cursor position end up out of bounds. ## References Technically this is a fix for issue #256, although that has been closed as "needs-repro". ## PR Checklist * [x] CLA signed. * [ ] Tests added/passed * [ ] Documentation updated. * [ ] Schema updated. * [x] I've discussed this with core contributors already. Issue number where discussion took place: #1976 ## Detailed Description of the Pull Request / Additional comments The main fix was to add checks in the `SetConsoleScreenBufferSizeImpl` and `SetConsoleScreenBufferInfoExImpl` methods, to make sure the viewport doesn't extend past the bottom or right of the buffer after a resize. If it has overflowed, we move the viewport back up or left until it's back within the buffer boundaries. We also check if the cursor position has ended up out of bounds, and if so, clamp it back inside the buffer. The `SCREEN_INFORMATION::SetViewport` was also a source of viewport overflow problems, because it was mistakenly using inclusive coordinates in its range checks, which resulted in them being off by one. That has now been corrected to use exclusive coordinates. Finally, the `IsCursorDoubleWidth` method was incorrectly marked as `noexcept`, which was preventing its exceptions from being caught. Ideally it shouldn't be throwing exceptions at all any more, but I've removed the `noexcept` specifier, so if it does throw an exception, it'll at least have more chance of recovering without a crash. ## Validation Steps Performed I put together a few test cases (based on the reports in issues #276 and #1976) which consistently caused conhost to crash, or to generate an exception visible in the debug output. With this PR applied, those test cases are no longer crashing or triggering exceptions. Closes #1976
claunia added the pull-request label 2026-01-31 09:20:21 +00:00
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Reference: starred/terminal#27161
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