CVE-2026-43434: rust_binder: check ownership before using vma

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

rust_binder: check ownership before using vma

When installing missing pages (or zapping them), Rust Binder will look
up the vma in the mm by address, and then call vm_insert_page (or
zap_page_range_single). However, if the vma is closed and replaced with
a different vma at the same address, this can lead to Rust Binder
installing pages into the wrong vma.

By installing the page into a writable vma, it becomes possible to write
to your own binder pages, which are normally read-only. Although you're
not supposed to be able to write to those pages, the intent behind the
design of Rust Binder is that even if you get that ability, it should not
lead to anything bad. Unfortunately, due to another bug, that is not the
case.

To fix this, store a pointer in vm_private_data and check that the vma
returned by vma_lookup() has the right vm_ops and vm_private_data before
trying to use the vma. This should ensure that Rust Binder will refuse
to interact with any other VMA. The plan is to introduce more vma
abstractions to avoid this unsafe access to vm_ops and vm_private_data,
but for now let's start with the simplest possible fix.

C Binder performs the same check in a slightly different way: it
provides a vm_ops->close that sets a boolean to true, then checks that
boolean after calling vma_lookup(), but this is more fragile
than the solution in this patch. (We probably still want to do both, but
the vm_ops->close callback will be added later as part of the follow-up
vma API changes.)

It's still possible to remap the vma so that pages appear in the right
vma, but at the wrong offset, but this is a separate issue and will be
fixed when Rust Binder gets a vm_ops->close callback.

The Linux kernel CVE team has assigned CVE-2026-43434 to this issue.


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

	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 6.18.19 with commit 20a01f20d1f4064d90a8627aa41b5987f0220bb9
	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 6.19.9 with commit 5a472d04fb4b9115fb7d1535bd885cea450f14db
	Issue introduced in 6.18 with commit eafedbc7c050c44744fbdf80bdf3315e860b7513 and fixed in 7.0 with commit 8ef2c15aeae07647f530d30f6daaf79eb801bcd1

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-2026-43434
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/page_range.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/20a01f20d1f4064d90a8627aa41b5987f0220bb9
	https://git.kernel.org/stable/c/5a472d04fb4b9115fb7d1535bd885cea450f14db
	https://git.kernel.org/stable/c/8ef2c15aeae07647f530d30f6daaf79eb801bcd1