CVE-2026-64469: binder: fix UAF in binder_thread_release()

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

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

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

binder: fix UAF in binder_thread_release()

When a thread exits, binder_thread_release() walks its transaction stack
to clear the t->from and t->to_proc that correspond with the exiting
thread. However, a process dying in parallel might attempt to kfree some
of these transactions. And if one of them has no associated t->to_proc,
the t->to_proc->inner_lock will not be acquired.

This means that transaction accesses in binder_thread_release() after
t->to_proc has been cleared might race with binder_free_transaction()
and cause a use-after-free error as reported by KASAN:

  ==================================================================
  BUG: KASAN: slab-use-after-free in binder_thread_release+0x5d0/0x798
  Write of size 8 at addr ffff000016627500 by task X/715

  CPU: 17 UID: 0 PID: 715 Comm: X Not tainted 7.1.0-rc5-00149-g8fde5d1d47f6 #30 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   binder_thread_release+0x5d0/0x798
   binder_ioctl+0x12c0/0x299c
   [...]

  Allocated by task 717 on cpu 18 at 67.267803s:
   __kasan_kmalloc+0xa0/0xbc
   __kmalloc_cache_noprof+0x174/0x444
   binder_transaction+0x554/0x8150
   binder_thread_write+0xa30/0x4354
   binder_ioctl+0x20f0/0x299c
   [...]

  Freed by task 202 on cpu 18 at 90.416221s:
   __kasan_slab_free+0x58/0x80
   kfree+0x1a0/0x4a4
   binder_free_transaction+0x150/0x294
   binder_send_failed_reply+0x398/0x6d8
   binder_release_work+0x3e4/0x4ec
   binder_deferred_func+0xbd8/0x104c
   [...]
  ==================================================================

In order to avoid this, make sure that binder_free_transaction() reads
the t->to_proc under the transaction lock. This will serialize the
transaction release with the accesses in binder_thread_release(). Plus,
it matches the documented locking rules for @to_proc.

The Linux kernel CVE team has assigned CVE-2026-64469 to this issue.


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

	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 5.10.261 with commit 1f96f8c0a6ed4f6d01d3dd29ad0cbf08dde96082
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 5.15.212 with commit df1a17abba8d6fac5f965adcb8113ceace6e4949
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 6.1.178 with commit 38e1a71728e5795b670cc159c18e286a40aeebb4
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 6.6.145 with commit faa070c7ad8ba25dcd0b12d7cdbb419e336f5391
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 6.12.96 with commit e63032dc715026a96bcaa13d375a8e15c91caa84
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 6.18.39 with commit ea02df466df60ecd758eb3b4df3f0cadc5c886ce
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 7.1.4 with commit ef5439ba5b9ac93349f5df12ef88b42a0ce26340
	Issue introduced in 4.14 with commit 7a4408c6bd3eb1dafba67986259191be081e3efb and fixed in 7.2-rc3 with commit 114a116aaa5f0295376cdf12da743c5bce3b20ce

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-2026-64469
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.c


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/1f96f8c0a6ed4f6d01d3dd29ad0cbf08dde96082
	https://git.kernel.org/stable/c/df1a17abba8d6fac5f965adcb8113ceace6e4949
	https://git.kernel.org/stable/c/38e1a71728e5795b670cc159c18e286a40aeebb4
	https://git.kernel.org/stable/c/faa070c7ad8ba25dcd0b12d7cdbb419e336f5391
	https://git.kernel.org/stable/c/e63032dc715026a96bcaa13d375a8e15c91caa84
	https://git.kernel.org/stable/c/ea02df466df60ecd758eb3b4df3f0cadc5c886ce
	https://git.kernel.org/stable/c/ef5439ba5b9ac93349f5df12ef88b42a0ce26340
	https://git.kernel.org/stable/c/114a116aaa5f0295376cdf12da743c5bce3b20ce