Chained function calls separated into multiple assignments #171
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Take the example from examples/vulnerable_code/sql/sqli.py:
`result = session.query(User).filter("username={}".format(TAINT))`
The `filter` function is marked as a sink. However, previously this did
not get marked as a vulnerability.
The call label used to be `session.query`, ignoring the filter function.
Now, when the file is read, it is transformed into 2 lines:
```
__chain_tmp_1 = session.query(User)
result = __chain_tmp_1.filter("username={}".format(TAINT))
```
And the vulnerability is found.
We don't find everything here: just ordinary assignments and return
statements. We can't just transform all Call nodes here since Call nodes
can appear in many different scenarios e.g. comprehensions, bare
function calls.
KevinHock
approved these changes
Sep 2, 2018
| class ChainedFunctionTransformer(): | ||
| def visit_chain(self, node, depth=1): | ||
| if ( | ||
| isinstance(node.value, ast.Call) and |
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Love how you did
node.value
node.value.func
node.value.func.value
in that order, it's super clean.
| inner_calls = self.visit_chain(unvisited_inner_call, depth + 1) | ||
| for inner_call_node in inner_calls: | ||
| ast.copy_location(inner_call_node, node) | ||
| outer_call = self.generic_visit(type(node)( |
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Indentation nit: This is awesomely smart but more indentation may make it clearer
outer_call = self.generic_visit(
type(node)(
value=ast.Call(
func=ast.Attribute(
value=ast.Name(id=temp_var_id, ctx=ast.Load()),
attr=call_node.func.attr,
ctx=ast.Load(),
),
args=call_node.args,
keywords=call_node.keywords,
),
**{field: value for field, value in ast.iter_fields(node) if field != 'value'} # e.g. targets
)
)Nit: w/r/t generic_visit, since it isn't defined in this class, maybe inheriting from ast.NodeTransformer in both classes would be clearer.
| self.assertIsInstance(transformed.body[0], ast.FunctionDef) | ||
|
|
||
| self.assertEqual(ast.dump(transformed), ast.dump(sync_tree)) | ||
|
|
||
| def test_chained_function(self): | ||
| chained_tree = ast.parse("\n".join([ |
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Take the example from examples/vulnerable_code/sql/sqli.py:
The
filterfunction is marked as a sink. However, previously this did not get marked as a vulnerability. The call label used to besession.query, ignoring the filter function.Now, when the file is read, it is transformed into 2 lines:
before converting to a CFG. The vulnerability is now found.
We don't find everything here: just ordinary assignments and return statements. We can't just transform all Call nodes here since Call nodes can appear in many different scenarios e.g. comprehensions, bare function calls. Because of this, it may be worth thinking about how to do this via the CFG everywhere function calls are chained.