Vyper: Return inside for loop more than 1 level deep — vyper
Insufficient Control Flow ManagementVVE-2020-0002
Earlier today, we received a responsible disclosure of a potential issue from @michwill (developer of @curvefi) for Vyper users who use return statements inside for loops of nested internal calls. Returning inside a for loop causes an invalid jump dest, reverting the transaction unnecessarily.
MWE:
@internal
def _baz():
for i in range(1):
return # Stack underflow happens here
@internal
def _bar():
self._baz()
@external
def foo():
self._bar()
Impact
Impact is minor, it is unlikely a user would encounter this problem unless they were working with nested calls, and return statements inside calls. Even in that scenario, you would encounter a revert which should be noticeable with adequate testing. In limited circumstances, this could cause a DoS attack for public contracts under certain conditions.
Patches
Fixed in https://github.com/vyperlang/vyper/pull/2110. Please upgrade to Vyper 0.2.3
Workarounds
Not returning inside a for loop nested 2+ internal calls deep works as is:
@internal
def _baz():
for i in range(1):
pass
return # This works fine
@internal
def _bar():
self._baz()
@external
def foo():
self._bar()
For more information
If you have any questions or comments about this advisory:
- Chat with us in our gitter
- Open an issue in https://github.com/vyperlang/vyper
- Email us at [email protected]
| Software | Affected versions |
|---|---|
vyper
|
>= 0.1.0b10, < 0.2.3 |
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