Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

rust_binder: use a u64 stride when cleaning up the offsets array

Allocation's Drop walks the offsets array (binder_size_t = u64 entries), cleaning up the objects, but it used usize instead of u64 for both the stride and the per-entry read.

On 64-bit kernels (usize == u64) this is harmless, but on 32-bit kernels it walks the 8-byte entries in 4-byte steps, iterating an N-entry array 2N times, and reads the always-zero high word as offset 0, cleaning up the object at offset 0 N extra times. As a result the referenced node or handle ends up with a lower reference count than it actually has (a refcount over-decrement), and binder's reference accounting is corrupted; for example, the owner can be notified of a strong reference release (BR_RELEASE) even though references still remain.

Change the stride to u64, and read each entry as a u64, narrowing it to usize with try_into().

On 32-bit ARM, when this over-decrement would drive a count below zero, the driver's existing refcount guard refuses it and fires:

rust_binder: Failure: refcount underflow!