fix(builtin): guard against missing args in builtins#943
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thevilledev wants to merge 1 commit intoexpr-lang:masterfrom
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fix(builtin): guard against missing args in builtins#943thevilledev wants to merge 1 commit intoexpr-lang:masterfrom
thevilledev wants to merge 1 commit intoexpr-lang:masterfrom
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The type checker skips argument validation for calls where the callee has unknown type (e.g. method calls on any-typed values). This allowed builtins like join() to reach runtime with zero arguments, panicking on args[0] access. Add runtime len(args) guards to a number of builtin functions that previously accessed args elements without bounds checking. Also fix date() to check len(args) a second time after stripping a leading *time.Location argument. Relates to OSS-Fuzz finding in expr-lang#941. Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
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Motivation
Relates to #941.
OSS-Fuzz finding has a fuzzed expression which calls
join()with zero arguments inside a method call on an any-typed value (e.g.fn().N(join())). The type checker'scallNode()skips argument validation when the callee resolves to an unknown type, so the invalid call passes compilation. At runtimejoin()accessesargs[0]on an empty slice, producing a Go runtime panic instead of a clean error.I found similar issues from other builtins, relying solely on compile-time validation that can be bypassed.
Changes
Add runtime
len(args)guards to a number of builtin functions. Each now returns a descriptive error. This error is already part of the allowlist in the fuzzing harness.I also removed some autogenerated test lines that called
firstandlastwith wrong arity. These tests were passing because ofdefer recover()silently swallowing the panic.Further comments
I think there is a chance to fix this in the checker, to provide compile-time rejection. But I guess it'll be quite complicated because of optional chaining on unknown types for a number of different expressions. This fix is the conservative kind just to have clean and descriptive runtime errors.