CVE-2026-64467: rust_binder: use a u64 stride when cleaning up the offsets array

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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!

The Linux kernel CVE team has assigned CVE-2026-64467 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 6.18.39 with commit 89b8cc948dce661af87527623b3a41cdd115e2f9
	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 7.1.4 with commit 74920b1b4e474ba7a4de4323c0458deec49d210b
	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 7.2-rc3 with commit 803c8a9502e9b97cd6ae937618ef4a8fd6274343

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64467
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/android/binder/allocation.rs


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/89b8cc948dce661af87527623b3a41cdd115e2f9
	https://git.kernel.org/stable/c/74920b1b4e474ba7a4de4323c0458deec49d210b
	https://git.kernel.org/stable/c/803c8a9502e9b97cd6ae937618ef4a8fd6274343