==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x27/0x4e0 net/l2tp/l2tp_core.c:1561
Write of size 8 at addr ffff888124f4b408 by task kworker/u4:8/3635
CPU: 1 PID: 3635 Comm: kworker/u4:8 Tainted: G W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
__dump_stack+0x21/0x24 lib/dump_stack.c:88
dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
print_address_description+0x71/0x210 mm/kasan/report.c:316
print_report+0x4a/0x60 mm/kasan/report.c:427
kasan_report+0x122/0x150 mm/kasan/report.c:531
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x280/0x290 mm/kasan/generic.c:189
__kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
l2tp_session_delete+0x27/0x4e0 net/l2tp/l2tp_core.c:1561
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1216 [inline]
l2tp_tunnel_del_work+0x201/0x420 net/l2tp/l2tp_core.c:1256
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Allocated by task 16026:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_alloc_info+0x25/0x30 mm/kasan/generic.c:505
____kasan_kmalloc mm/kasan/common.c:379 [inline]
__kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:388
kasan_kmalloc include/linux/kasan.h:212 [inline]
__do_kmalloc_node mm/slab_common.c:938 [inline]
__kmalloc+0xb1/0x1e0 mm/slab_common.c:951
kmalloc include/linux/slab.h:568 [inline]
kzalloc include/linux/slab.h:699 [inline]
l2tp_session_create+0x38/0xbe0 net/l2tp/l2tp_core.c:1597
pppol2tp_connect+0xb35/0x1570 net/l2tp/l2tp_ppp.c:781
__sys_connect_file net/socket.c:2001 [inline]
__sys_connect+0x398/0x420 net/socket.c:2018
__do_sys_connect net/socket.c:2028 [inline]
__se_sys_connect net/socket.c:2025 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2025
x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Freed by task 0:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x31/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x132/0x180 mm/kasan/common.c:241
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:249
kasan_slab_free include/linux/kasan.h:178 [inline]
slab_free_hook mm/slub.c:1745 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1771
slab_free mm/slub.c:3686 [inline]
__kmem_cache_free+0xb7/0x1b0 mm/slub.c:3702
kfree+0x6f/0xf0 mm/slab_common.c:990
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_dec_refcount+0xaf/0x1a0 net/l2tp/l2tp_core.c:205
pppol2tp_session_destruct+0xb1/0xf0 net/l2tp/l2tp_ppp.c:418
__sk_destruct+0x64/0x600 net/core/sock.c:2148
sk_destruct net/core/sock.c:2193 [inline]
__sk_free+0x313/0x410 net/core/sock.c:2204
sk_free+0x54/0x90 net/core/sock.c:2215
sock_put include/net/sock.h:2049 [inline]
pppol2tp_put_sk+0x7a/0xb0 net/l2tp/l2tp_ppp.c:401
rcu_do_batch+0x515/0xb90 kernel/rcu/tree.c:2297
rcu_core+0x5a5/0xe70 kernel/rcu/tree.c:2557
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2574
handle_softirqs+0x1d7/0x600 kernel/softirq.c:642
__do_softirq kernel/softirq.c:680 [inline]
invoke_softirq kernel/softirq.c:497 [inline]
__irq_exit_rcu+0x52/0xf0 kernel/softirq.c:729
irq_exit_rcu+0x9/0x10 kernel/softirq.c:741
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1118
asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:691
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
__call_rcu_common kernel/rcu/tree.c:2807 [inline]
call_rcu+0xd4/0xf90 kernel/rcu/tree.c:2926
pppol2tp_release+0x208/0x2d0 net/l2tp/l2tp_ppp.c:457
__sock_release net/socket.c:652 [inline]
sock_close+0xf1/0x290 net/socket.c:1390
__fput+0x1fc/0x8f0 fs/file_table.c:320
____fput+0x15/0x20 fs/file_table.c:348
task_work_run+0x1db/0x240 kernel/task_work.c:203
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0x9b/0xb0 kernel/entry/common.c:177
exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Second to last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
__call_rcu_common kernel/rcu/tree.c:2807 [inline]
call_rcu+0xd4/0xf90 kernel/rcu/tree.c:2926
pwq_unbound_release_workfn+0x287/0x2c0 kernel/workqueue.c:-1
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
The buggy address belongs to the object at ffff888124f4b400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
512-byte region [ffff888124f4b400, ffff888124f4b600)
The buggy address belongs to the physical page:
page:ffffea000493d200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x124f48
head:ffffea000493d200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100042f00
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x152a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 9747, tgid 9741 (syz.3.2876), ts 622703544985, free_ts 621038493847
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2637
prep_new_page+0x1c/0x110 mm/page_alloc.c:2644
get_page_from_freelist+0x2c7b/0x2cf0 mm/page_alloc.c:4544
__alloc_pages+0x1c3/0x450 mm/page_alloc.c:5858
alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
allocate_slab mm/slub.c:1962 [inline]
new_slab+0x98/0x3d0 mm/slub.c:2015
___slab_alloc+0x6f6/0xb50 mm/slub.c:3203
__slab_alloc+0x5e/0xa0 mm/slub.c:3302
slab_alloc_node mm/slub.c:3387 [inline]
__kmem_cache_alloc_node+0x203/0x2c0 mm/slub.c:3462
kmalloc_trace+0x29/0xb0 mm/slab_common.c:1028
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
tipc_crypto_start+0x9a/0x6a0 net/tipc/crypto.c:1475
tipc_init_net+0x221/0x360 net/tipc/core.c:72
ops_init+0x1c8/0x4a0 net/core/net_namespace.c:138
setup_net+0x4ab/0xcb0 net/core/net_namespace.c:335
copy_net_ns+0x355/0x5c0 net/core/net_namespace.c:481
create_new_namespaces+0x3a2/0x660 kernel/nsproxy.c:110
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1545 [inline]
free_pcp_prepare mm/page_alloc.c:1619 [inline]
free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3581
free_unref_page+0x8f/0x530 mm/page_alloc.c:3677
free_the_page mm/page_alloc.c:830 [inline]
__free_pages+0x67/0x100 mm/page_alloc.c:5947
__vunmap+0x9af/0xb70 mm/vmalloc.c:2731
__vfree mm/vmalloc.c:2780 [inline]
vfree+0x61/0x90 mm/vmalloc.c:2811
kcov_put kernel/kcov.c:437 [inline]
kcov_close+0x2b/0x50 kernel/kcov.c:533
__fput+0x1fc/0x8f0 fs/file_table.c:320
____fput+0x15/0x20 fs/file_table.c:348
task_work_run+0x1db/0x240 kernel/task_work.c:203
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0xa25/0x2650 kernel/exit.c:886
do_group_exit+0x210/0x2d0 kernel/exit.c:1028
get_signal+0x13b5/0x1520 kernel/signal.c:2889
arch_do_signal_or_restart+0xb0/0x1030 arch/x86/kernel/signal.c:871
exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
Memory state around the buggy address:
ffff888124f4b300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888124f4b380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888124f4b400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888124f4b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888124f4b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 3635 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 3635 Comm: kworker/u4:8 Tainted: G B W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 05 01 48 c7 c7 20 b0 a9 85 e8 4c e4 dd fe 0f 0b eb c3 e8 b3 a9 0c ff c6 05 44 c6 0b 05 01 48 c7 c7 80 b0 a9 85 e8 30 e4 dd fe <0f> 0b eb a7 e8 97 a9 0c ff c6 05 25 c6 0b 05 01 48 c7 c7 c0 af a9
RSP: 0018:ffffc90010e77c20 EFLAGS: 00010246
RAX: 8e663a4a5818cb00 RBX: 0000000000000003 RCX: ffff88810f103cc0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc90010e77c30 R08: dffffc0000000000 R09: fffff520021cef01
R10: fffff520021cef01 R11: 1ffff920021cef00 R12: 1ffff110249e9690
R13: ffff888124f4b400 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3510bff8 CR3: 000000010bf8f000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__refcount_sub_and_test include/linux/refcount.h:283 [inline]
__refcount_dec_and_test include/linux/refcount.h:315 [inline]
refcount_dec_and_test include/linux/refcount.h:333 [inline]
l2tp_session_dec_refcount+0xc8/0x1a0 net/l2tp/l2tp_core.c:204
l2tp_session_delete+0x3f0/0x4e0 net/l2tp/l2tp_core.c:1570
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1216 [inline]
l2tp_tunnel_del_work+0x201/0x420 net/l2tp/l2tp_core.c:1256
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
---[ end trace 0000000000000000 ]---