================================================================== BUG: KFENCE: use-after-free write in arch_atomic64_try_cmpxchg arch/x86/include/asm/atomic64_64.h:190 [inline] BUG: KFENCE: use-after-free write in arch_atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-long.h:443 [inline] BUG: KFENCE: use-after-free write in atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1669 [inline] BUG: KFENCE: use-after-free write in __mutex_trylock_fast kernel/locking/mutex.c:169 [inline] BUG: KFENCE: use-after-free write in mutex_lock+0xa0/0x1c0 kernel/locking/mutex.c:288 Use-after-free write at 0xffff88823ff24150 (in kfence-#42): arch_atomic64_try_cmpxchg arch/x86/include/asm/atomic64_64.h:190 [inline] arch_atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-long.h:443 [inline] atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1669 [inline] __mutex_trylock_fast kernel/locking/mutex.c:169 [inline] mutex_lock+0xa0/0x1c0 kernel/locking/mutex.c:288 pppol2tp_release+0x178/0x2b0 net/l2tp/l2tp_ppp.c:442 __sock_release net/socket.c:649 [inline] sock_close+0xb8/0x200 net/socket.c:1336 __fput+0x22b/0x900 fs/file_table.c:311 ____fput+0x15/0x20 fs/file_table.c:339 task_work_run+0x127/0x190 kernel/task_work.c:188 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline] syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x66/0xd0 kfence-#42: 0xffff88823ff24000-0xffff88823ff2419f, size=416, cache=kmalloc-512 allocated by task 2576 on cpu 1 at 140.666193s: kmalloc include/linux/slab.h:624 [inline] kzalloc include/linux/slab.h:750 [inline] l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772 __sys_connect_file net/socket.c:1923 [inline] __sys_connect+0x3cb/0x450 net/socket.c:1940 __do_sys_connect net/socket.c:1950 [inline] __se_sys_connect net/socket.c:1947 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1947 x64_sys_call+0x7c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 freed by task 2575 on cpu 1 at 140.675009s: l2tp_session_free net/l2tp/l2tp_core.c:168 [inline] l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193 l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589 pppol2tp_release+0x169/0x2b0 net/l2tp/l2tp_ppp.c:439 __sock_release net/socket.c:649 [inline] sock_close+0xb8/0x200 net/socket.c:1336 __fput+0x22b/0x900 fs/file_table.c:311 ____fput+0x15/0x20 fs/file_table.c:339 task_work_run+0x127/0x190 kernel/task_work.c:188 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline] syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x66/0xd0 CPU: 1 PID: 2575 Comm: syz.4.674 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 RIP: 0010:arch_atomic64_try_cmpxchg arch/x86/include/asm/atomic64_64.h:190 [inline] RIP: 0010:arch_atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-long.h:443 [inline] RIP: 0010:atomic_long_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1669 [inline] RIP: 0010:__mutex_trylock_fast kernel/locking/mutex.c:169 [inline] RIP: 0010:mutex_lock+0xa0/0x1c0 kernel/locking/mutex.c:288 Code: 04 00 48 c7 44 24 20 00 00 00 00 4c 89 f7 be 08 00 00 00 e8 32 d8 f5 fc 4c 89 ff be 08 00 00 00 e8 25 d8 f5 fc 48 8b 44 24 20 49 0f b1 1e 75 5d 48 c7 c0 80 b9 60 86 48 c1 e8 03 42 80 3c 20 RSP: 0000:ffffc90000a67ca0 EFLAGS: 00010256 RAX: 0000000000000000 RBX: ffff888135c86400 RCX: ffffffff84b3784b RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffffc90000a67cc0 RBP: ffffc90000a67d30 R08: ffffc90000a67cc7 R09: 1ffff9200014cf98 R10: dffffc0000000000 R11: fffff5200014cf99 R12: dffffc0000000000 R13: 1ffff9200014cf94 R14: ffff88823ff24150 R15: ffffc90000a67cc0 FS: 00005555707b6500(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff88823ff24150 CR3: 000000010f6ce000 CR4: 00000000003526a0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: pppol2tp_release+0x178/0x2b0 net/l2tp/l2tp_ppp.c:442 __sock_release net/socket.c:649 [inline] sock_close+0xb8/0x200 net/socket.c:1336 __fput+0x22b/0x900 fs/file_table.c:311 ____fput+0x15/0x20 fs/file_table.c:339 task_work_run+0x127/0x190 kernel/task_work.c:188 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline] syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x66/0xd0 RIP: 0033:0x7f4748ebc159 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fff0c721178 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007fff0c721260 RCX: 00007f4748ebc159 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00000000000226df R08: 0000000000000001 R09: 0000000000000000 R10: 0000001b2e220000 R11: 0000000000000246 R12: 00007fff0c7212a0 R13: 00007f4749143fac R14: 000000000002276c R15: 00007f4749143fa0 ================================================================== ---------------- Code disassembly (best guess): 0: 04 00 add $0x0,%al 2: 48 c7 44 24 20 00 00 movq $0x0,0x20(%rsp) 9: 00 00 b: 4c 89 f7 mov %r14,%rdi e: be 08 00 00 00 mov $0x8,%esi 13: e8 32 d8 f5 fc call 0xfcf5d84a 18: 4c 89 ff mov %r15,%rdi 1b: be 08 00 00 00 mov $0x8,%esi 20: e8 25 d8 f5 fc call 0xfcf5d84a 25: 48 8b 44 24 20 mov 0x20(%rsp),%rax * 2a: f0 49 0f b1 1e lock cmpxchg %rbx,(%r14) <-- trapping instruction 2f: 75 5d jne 0x8e 31: 48 c7 c0 80 b9 60 86 mov $0xffffffff8660b980,%rax 38: 48 c1 e8 03 shr $0x3,%rax 3c: 42 rex.X 3d: 80 .byte 0x80 3e: 3c 20 cmp $0x20,%al