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.Added the new error format to fuzzing harness allowlist (
not enough arguments to call x).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.