==================================================================
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 ffff88811c7d3c80 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 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 4843:
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 4844:
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_info_create+0xaa8/0x14d0 net/ipv6/route.c:3865
ip6_route_add+0x27/0x130 net/ipv6/route.c:3879
addrconf_add_mroute net/ipv6/addrconf.c:2535 [inline]
addrconf_add_dev+0x385/0x4c0 net/ipv6/addrconf.c:2553
inet6_addr_add+0x1a6/0x9d0 net/ipv6/addrconf.c:2993
inet6_rtm_newaddr+0x6e7/0x9c0 net/ipv6/addrconf.c:4978
rtnetlink_rcv_msg+0x9fd/0xcb0 net/core/rtnetlink.c:5662
netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2516
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5680
netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
netlink_unicast+0x86c/0xa30 net/netlink/af_netlink.c:1348
netlink_sendmsg+0x879/0xb80 net/netlink/af_netlink.c:1927
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
__sys_sendto+0x46d/0x620 net/socket.c:2063
__do_sys_sendto net/socket.c:2075 [inline]
__se_sys_sendto net/socket.c:2071 [inline]
__x64_sys_sendto+0xe5/0x100 net/socket.c:2071
x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
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
Second to 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
in_dev_finish_destroy+0x123/0x170 net/ipv4/devinet.c:255
in_dev_put include/linux/inetdevice.h:274 [inline]
inet_rcu_free_ifa+0x7b/0xd0 net/ipv4/devinet.c:225
rcu_do_batch+0x4c1/0xbf0 kernel/rcu/tree.c:2523
rcu_core+0x4a3/0xef0 kernel/rcu/tree.c:2763
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2776
handle_softirqs+0x250/0x560 kernel/softirq.c:583
__do_softirq kernel/softirq.c:621 [inline]
invoke_softirq kernel/softirq.c:443 [inline]
__irq_exit_rcu+0x52/0xf0 kernel/softirq.c:670
irq_exit_rcu+0x9/0x10 kernel/softirq.c:682
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1108
asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:676
The buggy address belongs to the object at ffff88811c7d3c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
512-byte region [ffff88811c7d3c00, ffff88811c7d3e00)
The buggy address belongs to the page:
page:ffffea000471f400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11c7d0
head:ffffea000471f400 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 0000000d00000001 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 140, ts 13285846390, 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]
__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]
alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6220
sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2542
unix_dgram_sendmsg+0x6f3/0x19b0 net/unix/af_unix.c:1816
unix_seqpacket_sendmsg+0x118/0x1e0 net/unix/af_unix.c:2277
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
sock_write_iter+0x2a6/0x3a0 net/socket.c:1080
do_iter_readv_writev+0x477/0x5f0 fs/read_write.c:-1
do_iter_write+0x207/0x7b0 fs/read_write.c:855
page_owner free stack trace missing
Memory state around the buggy address:
ffff88811c7d3b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88811c7d3c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88811c7d3c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88811c7d3d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88811c7d3d80: 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 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 c0 46 63 85 e8 fc 9e 5a 02 0f 0b eb c3 e8 03 9c 19 ff c6 05 50 0d 96 04 01 48 c7 c7 20 47 63 85 e8 e0 9e 5a 02 <0f> 0b eb a7 e8 e7 9b 19 ff c6 05 31 0d 96 04 01 48 c7 c7 60 46 63
RSP: 0018:ffffc900000a7c40 EFLAGS: 00010246
RAX: 5384056722b56400 RBX: 0000000000000003 RCX: ffff8881002713c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc900000a7c50 R08: ffff8881f7132f3f R09: 1ffff1103ee265e7
R10: dffffc0000000000 R11: ffffed103ee265e8 R12: ffff88811f230020
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007effe1fe02f8 CR3: 000000010d6f3000 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_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 b9a8c47ae6df80df ]---