Certain sequences with default parameters can trigger a crash

[j4james]

Windows Terminal version

1.17.1023

Windows build number

10.0.19045.2728

Other Software

No response

Steps to reproduce

1. Open a bash shell.
2. Execute printf "\e[\$r"

Expected Behavior

That sequence executes the DECCARA control with all default parameters. That should have the effect of resetting the attributes of everything on the screen.

Actual Behavior

The terminal hangs for a second, and then the tab closes (assumedly because the underlying conhost has crashed).

The problem arises when using the VTParameters::subspan method to access an offset beyond the end of the original span. Other than the DECCARA sequence, this can also be triggered by DECRARA and DECPS. In the latter case, the whole terminal can crash rather than just the active tab. That may just be a matter of chance though.

My suggested fix would be to change the VTParameters::subspan implementation here:

terminal/src/terminal/adapter/DispatchTypes.hpp

Line 187 in 5ed3c76

const auto subValues = _values.subspan(offset);

to something like this:

    const auto subValues = _values.subspan(std::min(offset, _values.size()));

That way an offset beyond the end of the source span would just produce an empty span (that's what I mistakenly assumed the subspan was already doing).