LruCache::pop() in lru was not panic-safe. If the Drop implementation of a stored key panics during pop(), self.detach() is never called, leaving dangling pointers in the internal doubly-linked list.
A subsequent cache operation that triggers eviction can then dereference these dangling pointers:
- The node is freed from the map, but remains linked in the LRU list due to the skipped
detach() call
- When a new insertion causes eviction, the LRU traversal encounters the dangling pointer
- This results in a write to already-freed memory during the eviction process
Impact
- CWE-416 (Use-After-Free): memory corruption when subsequent cache operations access freed node pointers in the linked list
- CWE-415 (Double Free): potential heap corruption when the same memory is freed multiple times
Both types of undefined behavior can be invoked in safe Rust, but only if unwinding panics are enabled and std::panic::catch_unwind is used with key types that have potentially-panicking Drop implementations.
Fix
Fixed in lru 0.18.2 by detaching the node from the linked list before freeing it and dropping the key (lru-rs#238).
lru0.16.3LruCache::pop()inlruwas not panic-safe. If theDropimplementation of a stored key panics duringpop(),self.detach()is never called, leaving dangling pointers in the internal doubly-linked list.A subsequent cache operation that triggers eviction can then dereference these dangling pointers:
detach()callImpact
Both types of undefined behavior can be invoked in safe Rust, but only if unwinding panics are enabled and
std::panic::catch_unwindis used with key types that have potentially-panickingDropimplementations.Fix
Fixed in
lru0.18.2 by detaching the node from the linked list before freeing it and dropping the key (lru-rs#238).