Vyper has incorrectly allocated named re-entrancy locks

Impact

In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically:

• A .vy contract compiled with either of the following vyper versions: 0.2.15, 0.2.16, 0.3.0
• A primary function that utilizes the @nonreentrant decorator with a specific key and does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates)
• A secondary function that utilizes the same key and would be affected by the improper state caused by the primary function

Patches

https://github.com/vyperlang/vyper/pull/2439, https://github.com/vyperlang/vyper/pull/2514

Workarounds

Upgrade to 0.3.1 or higher

References

Technical post-mortem report: https://hackmd.io/@vyperlang/HJUgNMhs2