Out of bounds co_* tuple access is allowed

[thatbirdguythatuknownot]

When a LOAD_* instruction needs to load from a co_*s tuple, it can segfault and crash the program when the index is out of bounds.
Examples:

eval(compile('a', '<string>', 'eval').replace(co_names=()))
eval((lambda:0).__code__.replace(co_consts=()))

[TeamSpen210]

This is intentional I believe for efficiency - there's many ways invalid bytecode can crash the eval loop, and fixing them would degrade performance. Easier to say "don't do that".

[thatbirdguythatuknownot]

This is intentional I believe for efficiency - there's many ways invalid bytecode can crash the eval loop, and fixing them would degrade performance. Easier to say "don't do that".

@TeamSpen210 I think it should be validated in a place like _PyCode_Validate, not the eval loop.

[sweeneyde]

See this comment from the "crashers" tests:

cpython/Lib/test/crashers/bogus_code_obj.py

Lines 2 to 11 in 2ef73be

	Broken bytecode objects can easily crash the interpreter.
	This is not going to be fixed. It is generally agreed that there is no
	point in writing a bytecode verifier and putting it in CPython just for
	this. Moreover, a verifier is bound to accept only a subset of all safe
	bytecodes, so it could lead to unnecessary breakage.
	For security purposes, "restricted" interpreters are not going to let
	the user build or load random bytecodes anyway. Otherwise, this is a
	"won't fix" case.

[kumaraditya303]

This isn't worth fixing as there are many ways to crash the interpreter with broken code objects.

cpython/Lib/test/crashers/bogus_code_obj.py

Lines 2 to 11 in 2ef73be

	Broken bytecode objects can easily crash the interpreter.
	This is not going to be fixed. It is generally agreed that there is no
	point in writing a bytecode verifier and putting it in CPython just for
	this. Moreover, a verifier is bound to accept only a subset of all safe
	bytecodes, so it could lead to unnecessary breakage.
	For security purposes, "restricted" interpreters are not going to let
	the user build or load random bytecodes anyway. Otherwise, this is a
	"won't fix" case.