==================================================================
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 ffff88813b122080 by task kworker/u4:10/2414
CPU: 1 PID: 2414 Comm: kworker/u4:10 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 3202:
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 3202:
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]
fib6_del_route net/ipv6/ip6_fib.c:1998 [inline]
fib6_del+0xbf0/0xf00 net/ipv6/ip6_fib.c:2031
fib6_clean_node+0x2a1/0x540 net/ipv6/ip6_fib.c:2193
fib6_walk_continue+0x54b/0x740 net/ipv6/ip6_fib.c:2115
fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2163
fib6_clean_tree net/ipv6/ip6_fib.c:2243 [inline]
__fib6_clean_all net/ipv6/ip6_fib.c:2259 [inline]
fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2270
rt6_sync_down_dev net/ipv6/route.c:4906 [inline]
rt6_disable_ip+0x12a/0x840 net/ipv6/route.c:4911
addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3809
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
xfrmi_exit_batch_net+0x20a/0x260 net/xfrm/xfrm_interface_core.c:769
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x605/0xae0 net/core/net_namespace.c:599
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
The buggy address belongs to the object at ffff88813b122000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff88813b122000, ffff88813b122200)
The buggy address belongs to the page:
page:ffffea0004ec4800 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88813b120000 pfn:0x13b120
head:ffffea0004ec4800 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004ec5100 0000000300000003 ffff888100042f00
raw: ffff88813b120000 000000008010000f 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 1421, ts 104926394878, free_ts 83629443071
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+0x16a/0x2c0 mm/slub.c:4432
kmalloc include/linux/slab.h:624 [inline]
kzalloc include/linux/slab.h:750 [inline]
fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:155
ip6_route_info_create+0x51b/0x14d0 net/ipv6/route.c:3783
ip6_route_add+0x27/0x130 net/ipv6/route.c:3879
addrconf_prefix_route+0x233/0x310 net/ipv6/addrconf.c:2478
inet6_addr_add+0x50b/0x9d0 net/ipv6/addrconf.c:3035
inet6_rtm_newaddr+0x6e7/0x9c0 net/ipv6/addrconf.c:4985
rtnetlink_rcv_msg+0x9fd/0xcb0 net/core/rtnetlink.c:5662
netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2520
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
__pagevec_release+0x71/0xe0 mm/swap.c:1035
pagevec_release include/linux/pagevec.h:81 [inline]
shmem_undo_range+0x564/0x13b0 mm/shmem.c:965
shmem_truncate_range mm/shmem.c:1064 [inline]
shmem_evict_inode+0x1dc/0x970 mm/shmem.c:1146
evict+0x4b6/0x8b0 fs/inode.c:650
iput_final fs/inode.c:1779 [inline]
iput+0x651/0x7e0 fs/inode.c:1805
dentry_unlink_inode+0x338/0x3e0 fs/dcache.c:380
__dentry_kill+0x45b/0x660 fs/dcache.c:586
dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
dput+0x47/0x90 fs/dcache.c:893
__fput+0x5c7/0x900 fs/file_table.c:319
____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
Memory state around the buggy address:
ffff88813b121f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88813b122000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88813b122080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88813b122100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88813b122180: 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: 2414 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 2414 Comm: kworker/u4:10 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 20 52 63 85 e8 8c 05 5b 02 0f 0b eb c3 e8 e3 8e 19 ff c6 05 e0 fa 95 04 01 48 c7 c7 80 52 63 85 e8 70 05 5b 02 <0f> 0b eb a7 e8 c7 8e 19 ff c6 05 c1 fa 95 04 01 48 c7 c7 c0 51 63
RSP: 0018:ffffc9000226fc40 EFLAGS: 00010246
RAX: b1a9f58820ea8000 RBX: 0000000000000003 RCX: ffff88811c02e2c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc9000226fc50 R08: ffff8881f7132f3f R09: 1ffff1103ee265e7
R10: dffffc0000000000 R11: ffffed103ee265e8 R12: ffff88813b120c20
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f847cac5dac CR3: 000000012584b000 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 8dac5860fa31efe6 ]---