New submission from Larry Hastings:
Peter's working on converting socket to use Argument Clinic. He had a default
that really should look like this:
min(SOME_SOCKET_MODULE_CONSTANT, 128)
"min" wasn't something we'd needed before. I thought about it and realized we
could do a much better job of simulating the evaluation context of a shared
module.
Initially I thought, all I needed was to bolster the environment we used for
eval() to add the builtins. (Which I've done.) But this wasn't sufficient
because we deliberately used ast.literal_eval(), which doesn't support function
calls by design for superior security. Or subscripting, or attribute access.
We already worked around those I think.
But how concerned are we about security? What is the attack vector here? If
the user is able to construct an object that has a villainous
__text_signature__ on it... surely they could already do as they like?
So here's a first draft at modifying the __text_signature__ evaluation
environment so it can handle much more sophisticated expressions. It can use
anything from builtins, or anything in sys.modules, or anything in the current
module; it can call functions, and subscript, and access attributes, and
everything.
To make this work I had to write an ast printer that produces evaluatable
Python code. Note that it's not complete, I know it's not complete, it's
missing loads of operators. Assume that if this is a good idea I will add all
the missing operators.
Nick was worried that *in the future* we might expose a "turn this string into
a signature" function. That might make an easier attack vector. So he asked
that the "trusted=" keyword flag be added, and the full-on eval only happen if
the string is trusted.
----------
assignee: larry
components: Library (Lib)
files: larry.improved.signature.expressions.1.txt
messages: 241140
nosy: larry, ncoghlan, pdmccormick, serhiy.storchaka, yselivanov, zach.ware
priority: normal
severity: normal
stage: patch review
status: open
title: Make inspect.signature expression evaluation more powerful
type: enhancement
versions: Python 3.5
Added file:
http://bugs.python.org/file39047/larry.improved.signature.expressions.1.txt
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<http://bugs.python.org/issue23967>
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