==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:826 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:883 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273
Read of size 8 at addr ffff8881299cf080 by task kworker/u4:4/381
CPU: 0 PID: 381 Comm: kworker/u4:4 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
__dump_stack+0x21/0x30 lib/dump_stack.c:88
dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:427 [inline]
kasan_report+0x10f/0x150 mm/kasan/report.c:444
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
hlist_unhashed include/linux/list.h:826 [inline]
hlist_del_init include/linux/list.h:883 [inline]
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline]
l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273
process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
Allocated by task 977:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:45 [inline]
set_alloc_info mm/kasan/common.c:433 [inline]
____kasan_kmalloc mm/kasan/common.c:512 [inline]
__kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
kasan_kmalloc include/linux/kasan.h:227 [inline]
__kmalloc+0x13d/0x2c0 mm/slub.c:4436
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 978:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
kasan_slab_free include/linux/kasan.h:193 [inline]
slab_free_hook mm/slub.c:1728 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
slab_free mm/slub.c:3526 [inline]
kfree+0xc4/0x270 mm/slub.c:4588
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
pppox_ioctl+0x1e4/0x320 drivers/net/ppp/pppox.c:93
sock_do_ioctl+0x103/0x310 net/socket.c:1138
sock_ioctl+0x459/0x6d0 net/socket.c:1257
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:860
__x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
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
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
__kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
__call_rcu_common kernel/rcu/tree.c:3011 [inline]
call_rcu+0x10b/0xf60 kernel/rcu/tree.c:3129
fib6_info_release include/net/ip6_fib.h:349 [inline]
ip6_route_add+0xe4/0x130 net/ipv6/route.c:3884
addrconf_add_mroute net/ipv6/addrconf.c:2535 [inline]
addrconf_add_dev+0x385/0x4c0 net/ipv6/addrconf.c:2553
addrconf_dev_config net/ipv6/addrconf.c:3432 [inline]
addrconf_init_auto_addrs+0x7ae/0xbd0 net/ipv6/addrconf.c:3520
addrconf_notify+0x95d/0xe00 net/ipv6/addrconf.c:3689
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
call_netdevice_notifiers_info net/core/dev.c:2070 [inline]
netdev_state_change+0x175/0x230 net/core/dev.c:1461
linkwatch_do_dev+0x115/0x160 net/core/link_watch.c:167
__linkwatch_run_queue+0x4b1/0x7c0 net/core/link_watch.c:213
linkwatch_event+0x4c/0x60 net/core/link_watch.c:252
process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
process_scheduled_works kernel/workqueue.c:2391 [inline]
worker_thread+0xd4c/0x1250 kernel/workqueue.c:2477
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
The buggy address belongs to the object at ffff8881299cf000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff8881299cf000, ffff8881299cf200)
The buggy address belongs to the page:
page:ffffea0004a67300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1299cc
head:ffffea0004a67300 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea00049aa900 0000000400000002 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 8, ts 23121889131, free_ts 0
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
__alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
alloc_slab_page mm/slub.c:-1 [inline]
allocate_slab mm/slub.c:1937 [inline]
new_slab+0xa0/0x4d0 mm/slub.c:2000
___slab_alloc+0x3ac/0x840 mm/slub.c:3033
__slab_alloc+0x49/0x90 mm/slub.c:3120
slab_alloc_node mm/slub.c:3211 [inline]
slab_alloc mm/slub.c:3255 [inline]
kmem_cache_alloc_trace+0x146/0x270 mm/slub.c:3272
kmalloc include/linux/slab.h:619 [inline]
kzalloc include/linux/slab.h:750 [inline]
ipv6_add_addr+0x408/0xd90 net/ipv6/addrconf.c:1119
addrconf_add_linklocal+0x209/0x660 net/ipv6/addrconf.c:3265
addrconf_addr_gen+0x53f/0x6a0 net/ipv6/addrconf.c:3396
addrconf_dev_config net/ipv6/addrconf.c:3441 [inline]
addrconf_init_auto_addrs+0x867/0xbd0 net/ipv6/addrconf.c:3520
addrconf_notify+0x95d/0xe00 net/ipv6/addrconf.c:3689
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
call_netdevice_notifiers_info net/core/dev.c:2070 [inline]
netdev_state_change+0x175/0x230 net/core/dev.c:1461
linkwatch_do_dev+0x115/0x160 net/core/link_watch.c:167
page_owner free stack trace missing
Memory state around the buggy address:
ffff8881299cef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881299cf000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881299cf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881299cf100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881299cf180: 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: 1 PID: 381 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 381 Comm: kworker/u4:4 Tainted: G B syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 40 47 63 85 e8 ac 67 5a 02 0f 0b eb c3 e8 43 80 19 ff c6 05 00 f5 95 04 01 48 c7 c7 a0 47 63 85 e8 90 67 5a 02 <0f> 0b eb a7 e8 27 80 19 ff c6 05 e1 f4 95 04 01 48 c7 c7 e0 46 63
RSP: 0018:ffffc90000d17c40 EFLAGS: 00010246
RAX: 082600d67301e100 RBX: 0000000000000003 RCX: ffff8881119a4f00
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90000d17c50 R08: ffff8881f7132f3f R09: 1ffff1103ee265e7
R10: dffffc0000000000 R11: ffffed103ee265e8 R12: ffff888128fca020
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f43d5532000 CR3: 00000001252c5000 CR4: 00000000003506a0
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_put+0xc8/0x1a0 net/l2tp/l2tp_core.c:192
l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1235 [inline]
l2tp_tunnel_del_work+0x180/0x3d0 net/l2tp/l2tp_core.c:1273
process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
---[ end trace b08cb8ce0fc705b9 ]---