==================================================================
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 ffff8881433c0c80 by task kworker/u4:4/397
CPU: 0 PID: 397 Comm: kworker/u4:4 Tainted: G W 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 13155:
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 13154:
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
The buggy address belongs to the object at ffff8881433c0c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff8881433c0c00, ffff8881433c0e00)
The buggy address belongs to the page:
page:ffffea00050cf000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1433c0
head:ffffea00050cf000 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 8, ts 593863203525, free_ts 593732111356
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]
__kmalloc_track_caller+0x169/0x2c0 mm/slub.c:4954
kmalloc_reserve net/core/skbuff.c:357 [inline]
__alloc_skb+0x210/0x730 net/core/skbuff.c:428
alloc_skb include/linux/skbuff.h:1183 [inline]
nlmsg_new include/net/netlink.h:953 [inline]
inet6_ifa_notify net/ipv6/addrconf.c:5543 [inline]
__ipv6_ifa_notify+0x200/0xe70 net/ipv6/addrconf.c:6198
addrconf_ifdown+0xdb1/0x1910 net/ipv6/addrconf.c:3926
addrconf_notify+0x3bd/0xe00 net/ipv6/addrconf.c:-1
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]
call_netdevice_notifiers_extack net/core/dev.c:2082 [inline]
call_netdevice_notifiers net/core/dev.c:2096 [inline]
dev_close_many+0x325/0x4d0 net/core/dev.c:1671
unregister_netdevice_many+0x477/0x1a00 net/core/dev.c:11152
ip6_tnl_exit_batch_net+0x3eb/0x440 net/ipv6/ip6_tunnel.c:2313
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1474 [inline]
free_pcp_prepare mm/page_alloc.c:1546 [inline]
free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3536
free_unref_page_list+0x138/0x9e0 mm/page_alloc.c:3673
release_pages+0x1264/0x12c0 mm/swap.c:1015
free_pages_and_swap_cache+0x86/0xa0 mm/swap_state.c:320
tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
tlb_flush_mmu mm/mmu_gather.c:247 [inline]
tlb_finish_mmu+0x17e/0x310 mm/mmu_gather.c:338
exit_mmap+0x43b/0x8b0 mm/mmap.c:3248
__mmput+0x92/0x300 kernel/fork.c:1185
mmput+0x50/0x150 kernel/fork.c:1208
exit_mm kernel/exit.c:555 [inline]
do_exit+0xacc/0x29a0 kernel/exit.c:877
do_group_exit+0x149/0x310 kernel/exit.c:1004
__do_sys_exit_group kernel/exit.c:1015 [inline]
__se_sys_exit_group kernel/exit.c:1013 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1013
x64_sys_call+0x832/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:232
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
Memory state around the buggy address:
ffff8881433c0b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881433c0c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881433c0c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881433c0d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881433c0d80: 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: 397 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 397 Comm: kworker/u4:4 Tainted: G B W 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 00 4b 63 85 e8 3c 69 5a 02 0f 0b eb c3 e8 a3 82 19 ff c6 05 50 f6 95 04 01 48 c7 c7 60 4b 63 85 e8 20 69 5a 02 <0f> 0b eb a7 e8 87 82 19 ff c6 05 31 f6 95 04 01 48 c7 c7 a0 4a 63
RSP: 0018:ffffc90009637c40 EFLAGS: 00010246
RAX: f5a984a67ad62c00 RBX: 0000000000000003 RCX: ffff8881139e13c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90009637c50 R08: ffff8881f7032f3f R09: 1ffff1103ee065e7
R10: dffffc0000000000 R11: ffffed103ee065e8 R12: ffff8881433c0020
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557ebe27d0 CR3: 000000010d71b000 CR4: 00000000003506b0
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 068bba22f6cb3915 ]---