==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x27/0x4e0 net/l2tp/l2tp_core.c:1561
Write of size 8 at addr ffff88810d114c08 by task kworker/u4:6/20870
CPU: 1 PID: 20870 Comm: kworker/u4:6 Tainted: G W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
__dump_stack+0x21/0x24 lib/dump_stack.c:88
dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
print_address_description+0x71/0x200 mm/kasan/report.c:316
print_report+0x4a/0x60 mm/kasan/report.c:420
kasan_report+0x122/0x150 mm/kasan/report.c:524
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x280/0x290 mm/kasan/generic.c:189
__kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
l2tp_session_delete+0x27/0x4e0 net/l2tp/l2tp_core.c:1561
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1216 [inline]
l2tp_tunnel_del_work+0x201/0x420 net/l2tp/l2tp_core.c:1256
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
Allocated by task 26356:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_alloc_info+0x25/0x30 mm/kasan/generic.c:505
____kasan_kmalloc mm/kasan/common.c:379 [inline]
__kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:388
kasan_kmalloc include/linux/kasan.h:212 [inline]
__do_kmalloc_node mm/slab_common.c:938 [inline]
__kmalloc+0xb1/0x1e0 mm/slab_common.c:951
kmalloc include/linux/slab.h:568 [inline]
kzalloc include/linux/slab.h:699 [inline]
l2tp_session_create+0x38/0xbe0 net/l2tp/l2tp_core.c:1597
pppol2tp_connect+0xb35/0x1570 net/l2tp/l2tp_ppp.c:781
__sys_connect_file net/socket.c:2001 [inline]
__sys_connect+0x398/0x420 net/socket.c:2018
__do_sys_connect net/socket.c:2028 [inline]
__se_sys_connect net/socket.c:2025 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2025
x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Freed by task 26358:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x31/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x132/0x180 mm/kasan/common.c:241
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:249
kasan_slab_free include/linux/kasan.h:178 [inline]
slab_free_hook mm/slub.c:1750 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
slab_free mm/slub.c:3712 [inline]
__kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
kfree+0x6f/0xf0 mm/slab_common.c:990
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_dec_refcount+0xaf/0x1a0 net/l2tp/l2tp_core.c:205
pppol2tp_session_destruct+0xb1/0xf0 net/l2tp/l2tp_ppp.c:418
__sk_destruct+0x64/0x600 net/core/sock.c:2148
sk_destruct net/core/sock.c:2193 [inline]
__sk_free+0x313/0x410 net/core/sock.c:2204
sk_free+0x54/0x90 net/core/sock.c:2215
sock_put include/net/sock.h:2049 [inline]
pppol2tp_put_sk+0x7a/0xb0 net/l2tp/l2tp_ppp.c:401
rcu_do_batch+0x515/0xb90 kernel/rcu/tree.c:2297
rcu_core+0x5a5/0xe70 kernel/rcu/tree.c:2557
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2574
handle_softirqs+0x1d7/0x600 kernel/softirq.c:642
__do_softirq kernel/softirq.c:680 [inline]
invoke_softirq kernel/softirq.c:497 [inline]
__irq_exit_rcu+0x52/0xf0 kernel/softirq.c:729
irq_exit_rcu+0x9/0x10 kernel/softirq.c:741
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1118
asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:691
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
__call_rcu_common kernel/rcu/tree.c:2807 [inline]
call_rcu+0xd4/0xf90 kernel/rcu/tree.c:2926
pppol2tp_release+0x208/0x2d0 net/l2tp/l2tp_ppp.c:457
__sock_release net/socket.c:652 [inline]
sock_close+0xf1/0x290 net/socket.c:1390
__fput+0x1fc/0x8f0 fs/file_table.c:320
____fput+0x15/0x20 fs/file_table.c:348
task_work_run+0x1db/0x240 kernel/task_work.c:203
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0x9b/0xb0 kernel/entry/common.c:177
exit_to_user_mode_prepare+0x5a/0xa0 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Second to last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
insert_work+0x51/0x300 kernel/workqueue.c:1368
__queue_work+0x9b1/0xd30 kernel/workqueue.c:1527
queue_work_on+0xd2/0x140 kernel/workqueue.c:1555
queue_work include/linux/workqueue.h:510 [inline]
__bpf_map_put kernel/bpf/syscall.c:661 [inline]
bpf_map_put+0x1cf/0x240 kernel/bpf/syscall.c:667
__bpf_free_used_maps kernel/bpf/core.c:2517 [inline]
bpf_free_used_maps kernel/bpf/core.c:2523 [inline]
bpf_prog_free_deferred+0x169/0x720 kernel/bpf/core.c:2562
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
The buggy address belongs to the object at ffff88810d114c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
512-byte region [ffff88810d114c00, ffff88810d114e00)
The buggy address belongs to the physical page:
page:ffffea0004344500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10d114
head:ffffea0004344500 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004c98d00 dead000000000002 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 1618, tgid 1618 (kworker/0:8), ts 1215989246967, free_ts 1209284567917
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2643
prep_new_page+0x1c/0x110 mm/page_alloc.c:2650
get_page_from_freelist+0x2c7b/0x2cf0 mm/page_alloc.c:4554
__alloc_pages+0x1c3/0x450 mm/page_alloc.c:5868
alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
allocate_slab mm/slub.c:1967 [inline]
new_slab+0x98/0x3d0 mm/slub.c:2020
___slab_alloc+0x6bd/0xb20 mm/slub.c:3177
__slab_alloc+0x5e/0xa0 mm/slub.c:3263
slab_alloc_node mm/slub.c:3348 [inline]
__kmem_cache_alloc_node+0x203/0x2c0 mm/slub.c:3423
__do_kmalloc_node mm/slab_common.c:937 [inline]
__kmalloc+0xa1/0x1e0 mm/slab_common.c:951
kmalloc include/linux/slab.h:568 [inline]
kzalloc include/linux/slab.h:699 [inline]
neigh_alloc net/core/neighbour.c:494 [inline]
___neigh_create+0x6f6/0x1e20 net/core/neighbour.c:648
__neigh_create+0x31/0x40 net/core/neighbour.c:737
ip6_finish_output2+0xa4f/0x1870 net/ipv6/ip6_output.c:129
__ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
ip6_finish_output+0x5f9/0xbb0 net/ipv6/ip6_output.c:216
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1d1/0x3b0 net/ipv6/ip6_output.c:237
dst_output include/net/dst.h:453 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x7e3/0xcf0 net/ipv6/ndisc.c:513
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1551 [inline]
free_pcp_prepare mm/page_alloc.c:1625 [inline]
free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3589
free_unref_page+0x8f/0x530 mm/page_alloc.c:3687
free_the_page mm/page_alloc.c:836 [inline]
__free_pages+0x67/0x100 mm/page_alloc.c:5957
__free_slab+0xca/0x1a0 mm/slub.c:2044
free_slab mm/slub.c:2059 [inline]
discard_slab mm/slub.c:2065 [inline]
__unfreeze_partials+0x160/0x190 mm/slub.c:2614
put_cpu_partial+0xa9/0x100 mm/slub.c:2690
__slab_free+0x1c4/0x280 mm/slub.c:3589
do_slab_free mm/slub.c:3666 [inline]
___cache_free+0xbf/0xd0 mm/slub.c:3722
qlink_free mm/kasan/quarantine.c:168 [inline]
qlist_free_all+0xc6/0x140 mm/kasan/quarantine.c:187
kasan_quarantine_reduce+0x14a/0x170 mm/kasan/quarantine.c:294
__kasan_slab_alloc+0x24/0x80 mm/kasan/common.c:310
kasan_slab_alloc include/linux/kasan.h:202 [inline]
slab_post_alloc_hook+0x4f/0x2d0 mm/slab.h:768
slab_alloc_node mm/slub.c:3382 [inline]
__kmem_cache_alloc_node+0x192/0x2c0 mm/slub.c:3423
kmalloc_trace+0x29/0xb0 mm/slab_common.c:1028
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
__kvm_set_memory_region+0x606/0x910 virt/kvm/kvm_main.c:2024
kvm_set_memory_region virt/kvm/kvm_main.c:2048 [inline]
kvm_vm_ioctl_set_memory_region+0x74/0xa0 virt/kvm/kvm_main.c:2060
Memory state around the buggy address:
ffff88810d114b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88810d114b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810d114c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88810d114c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810d114d00: 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: 20870 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 20870 Comm: kworker/u4:6 Tainted: G B W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 05 01 48 c7 c7 60 b6 a9 85 e8 8c bc dd fe 0f 0b eb c3 e8 c3 80 0c ff c6 05 53 9b 0b 05 01 48 c7 c7 c0 b6 a9 85 e8 70 bc dd fe <0f> 0b eb a7 e8 a7 80 0c ff c6 05 34 9b 0b 05 01 48 c7 c7 00 b6 a9
RSP: 0018:ffffc9000ecbfc20 EFLAGS: 00010246
RAX: f76eef826df30600 RBX: 0000000000000003 RCX: ffff88811a319440
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc9000ecbfc30 R08: dffffc0000000000 R09: fffff52001d97f01
R10: fffff52001d97f01 R11: 1ffff92001d97f00 R12: 1ffff11021a22990
R13: ffff88810d114c00 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2790a7 CR3: 0000000146307000 CR4: 00000000003506b0
DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 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_dec_refcount+0xc8/0x1a0 net/l2tp/l2tp_core.c:204
l2tp_session_delete+0x3f0/0x4e0 net/l2tp/l2tp_core.c:1570
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1216 [inline]
l2tp_tunnel_del_work+0x201/0x420 net/l2tp/l2tp_core.c:1256
process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
worker_thread+0xa29/0x11f0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
---[ end trace 0000000000000000 ]---