CVE-2023-52438

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