🇰🇷 한글 설명
Linux kernel의 ecryptfs 파일시스템에서 TAG 66 Packet 포맷 설명이 cipher code와 checksum 필드를 누락하여 할당된 버퍼가 3바이트 부족함. write_tag_66_packet() 함수에서 버퍼 끝을 넘어 메모리에 쓰기(slab-out-of-bounds)가 발생하여 메모리 손상 및 시스템 불안정 초래.
💡 쉬운 설명
암호화된 파일을 만들 때 필요한 메모리 공간을 잘못 계산해서 작은 공간에 데이터를 쓰려고 하면서 다른 메모리를 손상시킴. 로컬 사용자가 파일 생성을 통해 시스템 메모리를 침해할 수 있음.
🇺🇸 원문 (English)
In the Linux kernel, the following vulnerability has been resolved:
ecryptfs: Fix buffer size for tag 66 packet
The 'TAG 66 Packet Format' description is missing the cipher code and
checksum fields that are packed into the message packet. As a result,
the buffer allocated for the packet is 3 bytes too small and
write_tag_66_packet() will write up to 3 bytes past the end of the
buffer.
Fix this by increasing the size of the allocation so the whole packet
will always fit in the buffer.
This fixes the below kasan slab-out-of-bounds bug:
BUG: KASAN: slab-out-of-bounds in ecryptfs_generate_key_packet_set+0x7d6/0xde0
Write of size 1 at addr ffff88800afbb2a5 by task touch/181
CPU: 0 PID: 181 Comm: touch Not tainted 6.6.13-gnu #1 4c9534092be820851bb687b82d1f92a426598dc6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2/GNU Guix 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x4c/0x70
print_report+0xc5/0x610
? ecryptfs_generate_key_packet_set+0x7d6/0xde0
? kasan_complete_mode_report_info+0x44/0x210
? ecryptfs_generate_key_packet_set+0x7d6/0xde0
kasan_report+0xc2/0x110
? ecryptfs_generate_key_packet_set+0x7d6/0xde0
__asan_store1+0x62/0x80
ecryptfs_generate_key_packet_set+0x7d6/0xde0
? __pfx_ecryptfs_generate_key_packet_set+0x10/0x10
? __alloc_pages+0x2e2/0x540
? __pfx_ovl_open+0x10/0x10 [overlay 30837f11141636a8e1793533a02e6e2e885dad1d]
? dentry_open+0x8f/0xd0
ecryptfs_write_metadata+0x30a/0x550
? __pfx_ecryptfs_write_metadata+0x10/0x10
? ecryptfs_get_lower_file+0x6b/0x190
ecryptfs_initialize_file+0x77/0x150
ecryptfs_create+0x1c2/0x2f0
path_openat+0x17cf/0x1ba0
? __pfx_path_openat+0x10/0x10
do_filp_open+0x15e/0x290
? __pfx_do_filp_open+0x10/0x10
? __kasan_check_write+0x18/0x30
? _raw_spin_lock+0x86/0xf0
? __pfx__raw_spin_lock+0x10/0x10
? __kasan_check_write+0x18/0x30
? alloc_fd+0xf4/0x330
do_sys_openat2+0x122/0x160
? __pfx_do_sys_openat2+0x10/0x10
__x64_sys_openat+0xef/0x170
? __pfx___x64_sys_openat+0x10/0x10
do_syscall_64+0x60/0xd0
entry_SYSCALL_64_after_hwframe+0x6e/0xd8
RIP: 0033:0x7f00a703fd67
Code: 25 00 00 41 00 3d 00 00 41 00 74 37 64 8b 04 25 18 00 00 00 85 c0 75 5b 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 85 00 00 00 48 83 c4 68 5d 41 5c c3 0f 1f
RSP: 002b:00007ffc088e30b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007ffc088e3368 RCX: 00007f00a703fd67
RDX: 0000000000000941 RSI: 00007ffc088e48d7 RDI: 00000000ffffff9c
RBP: 00007ffc088e48d7 R08: 0000000000000001 R09: 0000000000000000
R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000941
R13: 0000000000000000 R14: 00007ffc088e48d7 R15: 00007f00a7180040
</TASK>
Allocated by task 181:
kasan_save_stack+0x2f/0x60
kasan_set_track+0x29/0x40
kasan_save_alloc_info+0x25/0x40
__kasan_kmalloc+0xc5/0xd0
__kmalloc+0x66/0x160
ecryptfs_generate_key_packet_set+0x6d2/0xde0
ecryptfs_write_metadata+0x30a/0x550
ecryptfs_initialize_file+0x77/0x150
ecryptfs_create+0x1c2/0x2f0
path_openat+0x17cf/0x1ba0
do_filp_open+0x15e/0x290
do_sys_openat2+0x122/0x160
__x64_sys_openat+0xef/0x170
do_syscall_64+0x60/0xd0
entry_SYSCALL_64_after_hwframe+0x6e/0xd8
📍 영향받는 시스템
Linux kernel 6.6.13 이전 버전에서 ecryptfs를 사용하는 모든 시스템
⚔️ 공격 벡터
로컬 공격자가 ecryptfs 마운트 포인트에서 새 파일을 생성할 때 write_tag_66_packet 함수 호출로 메모리 오버플로우 트리거
🛡️ 대응 방법
Linux kernel을 패치된 버전 이상으로 업데이트하여 TAG 66 Packet 버퍼 크기 증가
🔧 검증 코드
출력이 VULNERABLE이면 취약한 커널 버전에서 ecryptfs 활성화 상태임. 최신 커널 버전이면 안전하지만 ecryptfs 사용 시 업데이트 권장.
uname -r | grep -E '^(6\.[0-5]\.|6\.6\.[0-9]$)' && grep -q ecryptfs /proc/filesystems && echo 'VULNERABLE' || echo 'Check kernel version'