Description

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:
...

Classification

CVE ID: CVE-2023-52438

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/a53e15e592b4dcc91c3a3b8514e484a0bdbc53a3
https://git.kernel.org/stable/c/c8c1158ffb007197f31f9d9170cf13e4f34cbb5c
https://git.kernel.org/stable/c/8ad4d580e8aff8de2a4d57c5930fcc29f1ffd4a6
https://git.kernel.org/stable/c/9fa04c93f24138747807fe75b5591bb680098f56
https://git.kernel.org/stable/c/a49087ab93508b60d9b8add91707a22dda832869
https://git.kernel.org/stable/c/e074686e993ff1be5f21b085a3b1b4275ccd5727
https://git.kernel.org/stable/c/3f489c2067c5824528212b0fc18b28d51332d906

Timeline