🇰🇷 한글 설명
Linux 커널의 JFFS2 파일 시스템에서 jffs2_free_inode 함수 호출 시 초기화되지 않은 메모리 주소에 접근하여 발생하는 취약점입니다. 높은 부하가 발생하는 동시성 상황에서 iget_locked 함수가 inode를 파괴할 때, 특정 멤버가 초기화되지 않은 상태로 남게 되어 커널 패닉(Oops)을 유발할 수 있습니다.
💡 쉬운 설명
컴퓨터가 파일을 관리하는 과정에서 아직 준비되지 않은 잘못된 메모리 주소를 참조하여 시스템이 갑자기 멈추거나 오류가 발생하는 문제입니다. 특히 여러 작업이 동시에 몰릴 때 발생할 가능성이 높습니다.
🇺🇸 원문 (English)
In the Linux kernel, the following vulnerability has been resolved:
jffs2: Fix potential illegal address access in jffs2_free_inode
During the stress testing of the jffs2 file system,the following
abnormal printouts were found:
[ 2430.649000] Unable to handle kernel paging request at virtual address 0069696969696948
[ 2430.649622] Mem abort info:
[ 2430.649829] ESR = 0x96000004
[ 2430.650115] EC = 0x25: DABT (current EL), IL = 32 bits
[ 2430.650564] SET = 0, FnV = 0
[ 2430.650795] EA = 0, S1PTW = 0
[ 2430.651032] FSC = 0x04: level 0 translation fault
[ 2430.651446] Data abort info:
[ 2430.651683] ISV = 0, ISS = 0x00000004
[ 2430.652001] CM = 0, WnR = 0
[ 2430.652558] [0069696969696948] address between user and kernel address ranges
[ 2430.653265] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[ 2430.654512] CPU: 2 PID: 20919 Comm: cat Not tainted 5.15.25-g512f31242bf6 #33
[ 2430.655008] Hardware name: linux,dummy-virt (DT)
[ 2430.655517] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 2430.656142] pc : kfree+0x78/0x348
[ 2430.656630] lr : jffs2_free_inode+0x24/0x48
[ 2430.657051] sp : ffff800009eebd10
[ 2430.657355] x29: ffff800009eebd10 x28: 0000000000000001 x27: 0000000000000000
[ 2430.658327] x26: ffff000038f09d80 x25: 0080000000000000 x24: ffff800009d38000
[ 2430.658919] x23: 5a5a5a5a5a5a5a5a x22: ffff000038f09d80 x21: ffff8000084f0d14
[ 2430.659434] x20: ffff0000bf9a6ac0 x19: 0169696969696940 x18: 0000000000000000
[ 2430.659969] x17: ffff8000b6506000 x16: ffff800009eec000 x15: 0000000000004000
[ 2430.660637] x14: 0000000000000000 x13: 00000001000820a1 x12: 00000000000d1b19
[ 2430.661345] x11: 0004000800000000 x10: 0000000000000001 x9 : ffff8000084f0d14
[ 2430.662025] x8 : ffff0000bf9a6b40 x7 : ffff0000bf9a6b48 x6 : 0000000003470302
[ 2430.662695] x5 : ffff00002e41dcc0 x4 : ffff0000bf9aa3b0 x3 : 0000000003470342
[ 2430.663486] x2 : 0000000000000000 x1 : ffff8000084f0d14 x0 : fffffc0000000000
[ 2430.664217] Call trace:
[ 2430.664528] kfree+0x78/0x348
[ 2430.664855] jffs2_free_inode+0x24/0x48
[ 2430.665233] i_callback+0x24/0x50
[ 2430.665528] rcu_do_batch+0x1ac/0x448
[ 2430.665892] rcu_core+0x28c/0x3c8
[ 2430.666151] rcu_core_si+0x18/0x28
[ 2430.666473] __do_softirq+0x138/0x3cc
[ 2430.666781] irq_exit+0xf0/0x110
[ 2430.667065] handle_domain_irq+0x6c/0x98
[ 2430.667447] gic_handle_irq+0xac/0xe8
[ 2430.667739] call_on_irq_stack+0x28/0x54
The parameter passed to kfree was 5a5a5a5a, which corresponds to the target field of
the jffs_inode_info structure. It was found that all variables in the jffs_inode_info
structure were 5a5a5a5a, except for the first member sem. It is suspected that these
variables are not initialized because they were set to 5a5a5a5a during memory testing,
which is meant to detect uninitialized memory.The sem variable is initialized in the
function jffs2_i_init_once, while other members are initialized in
the function jffs2_init_inode_info.
The function jffs2_init_inode_info is called after iget_locked,
but in the iget_locked function, the destroy_inode process is triggered,
which releases the inode and consequently, the target member of the inode
is not initialized.In concurrent high pressure scenarios, iget_locked
may enter the destroy_inode branch as described in the code.
Since the destroy_inode functionality of jffs2 only releases the target,
the fix method is to set target to NULL in jffs2_i_init_once.
📍 영향받는 시스템
Linux kernel (JFFS2 파일 시스템을 사용하는 환경)
⚔️ 공격 벡터
고부하 상황에서의 동시성 제어 미흡을 이용한 커널 메모리 오염 및 시스템 중단
🛡️ 대응 방법
jffs2_i_init_once 함수 내에서 target 멤버를 NULL로 설정하여 초기화되지 않은 메모리 접근을 방지하는 커널 패치 적용
🔧 검증 코드
현재 실행 중인 커널 버전을 확인하여 해당 취약점이 수정된 최신 보안 패치 버전인지 확인합니다.