🇰🇷 한글 설명
Linux 커널의 binder 구성 요소에서 shrinker 콜백 실행 중 use-after-free 취약점이 발견되었습니다. mmap 읽기 잠금을 사용하는 동안 vma 포인터를 참조하여 munmap() 작업과 경합이 발생할 수 있으며, 이는 메모리 손상이나 시스템 불안정을 초래할 수 있습니다.
💡 쉬운 설명
컴퓨터가 메모리를 정리하는 과정에서 이미 삭제된 메모리 주소를 다시 사용하려고 시도하여 발생하는 오류입니다. 이로 인해 시스템이 멈추거나 해커가 시스템 권한을 탈취할 위험이 있습니다.
🇺🇸 원문 (English)
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.
📍 영향받는 시스템
Linux kernel (binder driver 사용 환경)
⚔️ 공격 벡터
메모리 회수(page reclaiming)를 유도하여 munmap()과 shrinker 콜백 간의 레이스 컨디션을 발생시킴
🛡️ 대응 방법
커널을 최신 보안 패치가 적용된 버전으로 업데이트하거나, vma_lookup()을 사용하는 수정된 커널을 적용하십시오.
🔧 검증 코드
출력된 커널 버전이 취약점이 해결된 패치 버전(commit dd2283f2605e 이후)인지 확인하십시오.