concurrent-ruby is a modern concurrency tools for Ruby. Prior to 1.3.7, Concurrent::ReentrantReadWriteLock can incorrectly grant a write lock after one thread acquires the read lock 32,768 times. The lock stores a threads local read and write hold counts in one integer. The low 15 bits are used for the read hold count, and bit 15 is used as WRITE_LOCK_HELD. After 32,768 reentrant read acquisitions, the local read count crosses into the write-lock bit. try_write_lock then treats the thread as already holding a write lock and returns true without setting the global RUNNING_WRITER bit. This breaks the core mutual-exclusion guarantee: the caller is told it has a write lock, but other threads can still hold or acquire read locks at the same time. This vulnerability is fixed in 1.3.7.
Weakness
Wrap around errors occur whenever a value is incremented past the maximum value for its type and therefore “wraps around” to a very small, negative, or undefined value.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Concurrent_ruby | Rubyconcurrency | * | 1.3.7 (excluding) |
| Ruby-concurrent | Ubuntu | questing | * |
| Ruby-concurrent | Ubuntu | upstream | * |