==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:833 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:890 [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 ffff88810f9ca480 by task kworker/u4:1/10
CPU: 1 PID: 10 Comm: kworker/u4:1 Tainted: G W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
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:833 [inline]
hlist_del_init include/linux/list.h:890 [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 4127:
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 4128:
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+0x1e1/0x440 drivers/net/ppp/pppox.c:110
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 ffff88810f9ca400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff88810f9ca400, ffff88810f9ca600)
The buggy address belongs to the page:
page:ffffea00043e7200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10f9c8
head:ffffea00043e7200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100042f00
raw: 0000000000000000 0000000080100010 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 407, ts 84679409527, free_ts 83879371826
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2610
prep_new_page+0x1c/0x110 mm/page_alloc.c:2616
get_page_from_freelist+0x2d42/0x2dd0 mm/page_alloc.c:4492
__alloc_pages+0x1a2/0x460 mm/page_alloc.c:5829
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+0x16a/0x2c0 mm/slub.c:4432
kmalloc include/linux/slab.h:624 [inline]
kzalloc include/linux/slab.h:750 [inline]
neigh_alloc net/core/neighbour.c:438 [inline]
___neigh_create+0x6fb/0x1c50 net/core/neighbour.c:591
__neigh_create+0x31/0x40 net/core/neighbour.c:679
ip6_finish_output2+0xae3/0x1790 net/ipv6/ip6_output.c:129
__ip6_finish_output+0x623/0x7e0 net/ipv6/ip6_output.c:203
ip6_finish_output+0x31/0x220 net/ipv6/ip6_output.c:213
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1fa/0x410 net/ipv6/ip6_output.c:236
dst_output include/net/dst.h:453 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x7f8/0xd00 net/ipv6/ndisc.c:513
ndisc_send_ns+0x879/0xb10 net/ipv6/ndisc.c:655
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1477 [inline]
free_pcp_prepare mm/page_alloc.c:1549 [inline]
free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3540
free_unref_page+0xae/0x540 mm/page_alloc.c:3622
free_the_page mm/page_alloc.c:808 [inline]
__free_pages+0x6c/0x100 mm/page_alloc.c:5905
__free_slab+0xe5/0x1e0 mm/slub.c:2025
free_slab mm/slub.c:2040 [inline]
discard_slab mm/slub.c:2046 [inline]
__unfreeze_partials+0x15a/0x190 mm/slub.c:2532
put_cpu_partial+0xc6/0x120 mm/slub.c:2612
__slab_free+0x1d4/0x290 mm/slub.c:3395
do_slab_free mm/slub.c:3514 [inline]
___cache_free+0x104/0x120 mm/slub.c:3535
qlink_free+0x4d/0x90 mm/kasan/quarantine.c:157
qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176
kasan_quarantine_reduce+0x14a/0x170 mm/kasan/quarantine.c:283
__kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:443
kasan_slab_alloc include/linux/kasan.h:217 [inline]
slab_post_alloc_hook+0x4f/0x2b0 mm/slab.h:550
slab_alloc_node mm/slub.c:3245 [inline]
slab_alloc mm/slub.c:3255 [inline]
kmem_cache_alloc_trace+0xfb/0x270 mm/slub.c:3272
kmalloc include/linux/slab.h:619 [inline]
kzalloc include/linux/slab.h:750 [inline]
kobject_uevent_env+0x271/0x700 lib/kobject_uevent.c:539
kobject_uevent+0x1d/0x30 lib/kobject_uevent.c:657
Memory state around the buggy address:
ffff88810f9ca380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88810f9ca400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810f9ca480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88810f9ca500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810f9ca580: 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: 10 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 10 Comm: kworker/u4:1 Tainted: G B W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 e0 57 63 85 e8 5c d0 5b 02 0f 0b eb c3 e8 13 59 19 ff c6 05 f2 c4 95 04 01 48 c7 c7 40 58 63 85 e8 40 d0 5b 02 <0f> 0b eb a7 e8 f7 58 19 ff c6 05 d3 c4 95 04 01 48 c7 c7 80 57 63
RSP: 0018:ffffc900000a7c40 EFLAGS: 00010246
RAX: 3252ead95e5ffa00 RBX: 0000000000000003 RCX: ffff888100270000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc900000a7c50 R08: ffff8881f7132eff R09: 1ffff1103ee265df
R10: dffffc0000000000 R11: ffffed103ee265e0 R12: ffff88810f9c8020
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1b47efb000 CR3: 000000010cad0000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
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 c170e0e5bdf45fe2 ]---