Looking at the results of the the previous DCA run, there was a bunch of
false positives where `bind` was being used with a `AF_UNIX` socket (a
filesystem path encoded as a string), not a `(host, port)` tuple. These
results should be excluded from the query, as they are not vulnerable.
Ideally, we would just add `.TupleElement[0]` to the MaD sink, except we
don't actually support this in Python MaD...
So, instead I opted for a more low-tech solution: check that the
argument in question flows from a tuple in the local scope.
This eliminates a bunch of false positives on `python/cpython` leaving
behind four true positive results.
This takes care of most of the false negatives from the preceding
commit.
Additionally, we add models for some known wrappers of `socket.socket`
from the `gevent` and `eventlet` packages.
Adds test cases from github/codeql#21582 demonstrating false negatives:
- Address stored in class attribute (`self.bind_addr`)
- `os.environ.get` with insecure default value
- `gevent.socket` (alternative socket module)
By limiting the results to the class that actually defines the `__del__`
method, we eliminate a bunch of FPs where a _subclass_ of such a class
would also get flagged.
For module-level metaclass declarations, we now also check that the
right hand side in a `__metaclass__ = type` assignment is in fact the
built-in `type`.
These could arguably be moved to `Class` itself, but for now I'm
choosing to limit the changes to the `DuckTyping` module (until we
decide on a proper API).
This module (which for convenience currently resides inside
`DataFlowDispatch`, but this may change later) contains convenience
predicates for bridging the gap between the data-flow layer and the old
points-to analysis.
The fix may look a bit obscure, so here's what's going on.
When we see `from . import helper`, we create an `ImportExpr` with level
equal to 1 (corresponding to the number of dots). To resolve such
imports, we compute the name of the enclosing package, as part of
`ImportExpr.qualifiedTopName()`. For this form of import expression, it
is equivalent to `this.getEnclosingModule().getPackageName()`. But
`qualifiedTopName` requires that `valid_module_name` holds for its
result, and this was _not_ the case for namespace packages.
To fix this, we extend `valid_module_name` to include the module names
of _any_ folder, not just regular package (which are the ones where
there's a `__init__.py` in the folder). Note that this doesn't simply
include all folders -- only the ones that result in valid module names
in Python.
