🇰🇷 한글 설명
Linux 커널의 netrom 네트워크 프로토콜 드라이버에서 nr_rt_ioctl() 함수 실행 중 두 개의 스핀락(nr_node_list_lock, nr_node->node_lock) 사이의 순환 의존성으로 인한 데드락 취약점입니다. 악의적인 로컬 사용자가 특정 IOCTL 명령을 실행하여 시스템을 교착 상태로 빠뜨릴 수 있습니다.
💡 쉬운 설명
Linux 커널의 netrom 네트워크 기능에서 두 개의 잠금 메커니즘이 잘못된 순서로 획득되어 서로를 기다리는 데드락 상태가 발생할 수 있습니다. 로컬 접근이 가능한 공격자가 이를 악용해 시스템을 응답 불가 상태로 만들 수 있습니다.
🇺🇸 원문 (English)
In the Linux kernel, the following vulnerability has been resolved:
netrom: fix possible dead-lock in nr_rt_ioctl()
syzbot loves netrom, and found a possible deadlock in nr_rt_ioctl [1]
Make sure we always acquire nr_node_list_lock before nr_node_lock(nr_node)
[1]
WARNING: possible circular locking dependency detected
6.9.0-rc7-syzkaller-02147-g654de42f3fc6 #0 Not tainted
------------------------------------------------------
syz-executor350/5129 is trying to acquire lock:
ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:464 [inline]
ffff8880186e2070 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1bb/0x1090 net/netrom/nr_route.c:697
but task is already holding lock:
ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:462 [inline]
ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x10a/0x1090 net/netrom/nr_route.c:697
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (nr_node_list_lock){+...}-{2:2}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x35/0x50 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_remove_node net/netrom/nr_route.c:299 [inline]
nr_del_node+0x4b4/0x820 net/netrom/nr_route.c:355
nr_rt_ioctl+0xa95/0x1090 net/netrom/nr_route.c:683
sock_do_ioctl+0x158/0x460 net/socket.c:1222
sock_ioctl+0x629/0x8e0 net/socket.c:1341
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:890
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&nr_node->node_lock){+...}-{2:2}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x35/0x50 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
nr_node_lock include/net/netrom.h:152 [inline]
nr_dec_obs net/netrom/nr_route.c:464 [inline]
nr_rt_ioctl+0x1bb/0x1090 net/netrom/nr_route.c:697
sock_do_ioctl+0x158/0x460 net/socket.c:1222
sock_ioctl+0x629/0x8e0 net/socket.c:1341
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:890
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(nr_node_list_lock);
lock(&nr_node->node_lock);
lock(nr_node_list_lock);
lock(&nr_node->node_lock);
*** DEADLOCK ***
1 lock held by syz-executor350/5129:
#0: ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
#0: ffffffff8f7053b8 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:462 [inline]
#0: ffffffff8f70
---truncated---
📍 영향받는 시스템
Linux kernel 6.9.0-rc7 이전 버전, netrom 프로토콜 지원 시스템
⚔️ 공격 벡터
Local, unprivileged user via IOCTL (ioctl syscall with nr_rt_ioctl)
🛡️ 대응 방법
Linux kernel 6.9.0-rc7 이후 버전으로 업데이트 (nr_rt_ioctl()에서 잠금 순서 수정)
🔧 검증 코드
커널 버전이 6.9.0-rc7 이전이면 취약점 가능성 있음. 현재 커널 버전이 6.9.0-rc8 이상이거나 공식 6.9+ 릴리스면 패치됨.
uname -r | grep -E '6\.[0-8]\.|6\.9\.0-rc[0-7]' && echo 'Potentially Vulnerable' || echo 'Check manually'