Subject: CVE-2023-21661: binder: fix use-after-free in shinker's callback

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

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

binder: fix use-after-free in shinker's callback

The mmap read lock is used during the shrinker's callback, which means
that using alloc->vma pointer isn't safe as it can race with munmap().
As of commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in
munmap") the mmap lock is downgraded after the vma has been isolated.

I was able to reproduce this issue by manually adding some delays and
triggering page reclaiming through the shrinker's debug sysfs. The
following KASAN report confirms the UAF:

  ==================================================================
  BUG: KASAN: slab-use-after-free in zap_page_range_single+0x470/0x4b8
  Read of size 8 at addr ffff356ed50e50f0 by task bash/478

  CPU: 1 PID: 478 Comm: bash Not tainted 6.6.0-rc5-00055-g1c8b86a3799f-dirty #70
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   zap_page_range_single+0x470/0x4b8
   binder_alloc_free_page+0x608/0xadc
   __list_lru_walk_one+0x130/0x3b0
   list_lru_walk_node+0xc4/0x22c
   binder_shrink_scan+0x108/0x1dc
   shrinker_debugfs_scan_write+0x2b4/0x500
   full_proxy_write+0xd4/0x140
   vfs_write+0x1ac/0x758
   ksys_write+0xf0/0x1dc
   __arm64_sys_write+0x6c/0x9c

  Allocated by task 492:
   kmem_cache_alloc+0x130/0x368
   vm_area_alloc+0x2c/0x190
   mmap_region+0x258/0x18bc
   do_mmap+0x694/0xa60
   vm_mmap_pgoff+0x170/0x29c
   ksys_mmap_pgoff+0x290/0x3a0
   __arm64_sys_mmap+0xcc/0x144

  Freed by task 491:
   kmem_cache_free+0x17c/0x3c8
   vm_area_free_rcu_cb+0x74/0x98
   rcu_core+0xa38/0x26d4
   rcu_core_si+0x10/0x1c
   __do_softirq+0x2fc/0xd24

  Last potentially related work creation:
   __call_rcu_common.constprop.0+0x6c/0xba0
   call_rcu+0x10/0x1c
   vm_area_free+0x18/0x24
   remove_vma+0xe4/0x118
   do_vmi_align_munmap.isra.0+0x718/0xb5c
   do_vmi_munmap+0xdc/0x1fc
   __vm_munmap+0x10c/0x278
   __arm64_sys_munmap+0x58/0x7c

Fix this issue by performing instead a vma_lookup() which will fail to
find the vma that was isolated before the mmap lock downgrade. Note that
this option has better performance than upgrading to a mmap write lock
which would increase contention. Plus, mmap_write_trylock() has been
recently removed anyway.

The Linux kernel CVE team has assigned CVE-2023-21661 to this issue.

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

	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 5.4.268 with commit a53e15e592b4
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 5.10.209 with commit c8c1158ffb00
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 5.15.148 with commit 8ad4d580e8af
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 6.1.74 with commit 9fa04c93f241
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 6.6.13 with commit a49087ab9350
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 6.7.1 with commit e074686e993f
	Issue introduced in 4.20 with commit dd2283f2605e and fixed in 6.8-rc1 with commit 3f489c2067c5

Please see https://www.kernel.org or 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-2023-21661
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_alloc.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/a53e15e592b4
	https://git.kernel.org/stable/c/c8c1158ffb00
	https://git.kernel.org/stable/c/8ad4d580e8af
	https://git.kernel.org/stable/c/9fa04c93f241
	https://git.kernel.org/stable/c/a49087ab9350
	https://git.kernel.org/stable/c/e074686e993f
	https://git.kernel.org/stable/c/3f489c2067c5