fix(vm): validate arg count before OpCall#904
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antonmedv merged 1 commit intoexpr-lang:masterfrom Jan 15, 2026
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Prevent index out of bounds panic when calling a function with more
arguments than it accepts. The VM now validates argument count before
attempting to access parameter types. Includes a regression test.
This issue was discovered by clusterfuzz with the expression:
$env(''matches' '? :now().UTC(g).d)//
Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
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Motivation
See OSS-Fuzz finding #903. The expression
$env(''matches' '? :now().UTC(g).d)//caused:The expression bypasses compile-time type checking due to
$env(...)being treated as an unknown type. Also the ternary operator deferring evaluation. Then at runtimeUTC()is called with an argument - even though it takes none. When theOpCallhandler accessesfnType.In(0)without checking its length, an index out of bounds panic happens, although recovered by the VM.Changes
Added argument count validation in VM before attempting to call functions. Including a regression test.
Further comments
Functions that return no values are already caught by the checker at compile time, so the
out[0]access afterfn.Call()remains safe.Regression from #889.
Nice edge case catched by the fuzzer.