==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x24/0x4a0 net/l2tp/l2tp_core.c:1563
Write of size 8 at addr ffff8881354d5c08 by task kworker/u4:2/3695
CPU: 1 PID: 3695 Comm: kworker/u4:2 Tainted: G W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
__dump_stack+0x21/0x30 lib/dump_stack.c:88
dump_stack_lvl+0xee/0x150 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+0xf1/0x140 mm/kasan/report.c:444
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:101 [inline]
test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
l2tp_session_delete+0x24/0x4a0 net/l2tp/l2tp_core.c:1563
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
l2tp_tunnel_del_work+0x1d2/0x3e0 net/l2tp/l2tp_core.c:1258
process_one_work+0x6be/0xba0 kernel/workqueue.c:2325
worker_thread+0xa59/0x1200 kernel/workqueue.c:2472
kthread+0x411/0x500 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
Allocated by task 6746:
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+0xda/0x110 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:1599
pppol2tp_connect+0xb35/0x1570 net/l2tp/l2tp_ppp.c:782
__sys_connect_file net/socket.c:1923 [inline]
__sys_connect+0x389/0x410 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 6754:
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_dec_refcount+0xaf/0x1a0 net/l2tp/l2tp_core.c:205
pppol2tp_session_destruct+0xb1/0xf0 net/l2tp/l2tp_ppp.c:419
__sk_destruct+0x56/0x5e0 net/core/sock.c:1967
sk_destruct net/core/sock.c:2012 [inline]
__sk_free+0x313/0x410 net/core/sock.c:2023
sk_free+0x54/0x90 net/core/sock.c:2034
sock_put include/net/sock.h:1975 [inline]
pppol2tp_put_sk+0x7a/0xb0 net/l2tp/l2tp_ppp.c:402
rcu_do_batch+0x51d/0xba0 kernel/rcu/tree.c:2523
rcu_core+0x5e4/0xf80 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
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+0x105/0xfe0 kernel/rcu/tree.c:3129
pppol2tp_release+0x208/0x2d0 net/l2tp/l2tp_ppp.c:458
__sock_release net/socket.c:649 [inline]
sock_close+0xe0/0x270 net/socket.c:1336
__fput+0x20b/0x8b0 fs/file_table.c:311
____fput+0x15/0x20 fs/file_table.c:339
task_work_run+0x127/0x190 kernel/task_work.c:188
get_signal+0x13fb/0x1480 kernel/signal.c:2679
arch_do_signal_or_restart+0xc1/0x10f0 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
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
kvfree_call_rcu+0xae/0x7e0 kernel/rcu/tree.c:3648
neigh_destroy+0x44f/0x590 net/core/neighbour.c:860
neigh_release include/net/neighbour.h:427 [inline]
neigh_cleanup_and_release+0x76/0x1a0 net/core/neighbour.c:103
neigh_del net/core/neighbour.c:197 [inline]
neigh_remove_one+0x379/0x400 net/core/neighbour.c:218
neigh_forced_gc net/core/neighbour.c:251 [inline]
neigh_alloc net/core/neighbour.c:429 [inline]
___neigh_create+0x492/0x1be0 net/core/neighbour.c:591
__neigh_create+0x31/0x40 net/core/neighbour.c:679
ip6_finish_output2+0xab3/0x1760 net/ipv6/ip6_output.c:127
__ip6_finish_output+0x61e/0x7d0 net/ipv6/ip6_output.c:201
ip6_finish_output+0x31/0x240 net/ipv6/ip6_output.c:211
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1d1/0x3b0 net/ipv6/ip6_output.c:234
dst_output include/net/dst.h:453 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x797/0xc70 net/ipv6/ndisc.c:513
ndisc_send_rs+0x6e5/0x960 net/ipv6/ndisc.c:707
addrconf_rs_timer+0x2c7/0x600 net/ipv6/addrconf.c:3980
call_timer_fn+0x38/0x290 kernel/time/timer.c:1457
expire_timers kernel/time/timer.c:1502 [inline]
__run_timers+0x639/0x9a0 kernel/time/timer.c:1773
run_timer_softirq+0x6a/0xf0 kernel/time/timer.c:1786
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 ffff8881354d5c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
512-byte region [ffff8881354d5c00, ffff8881354d5e00)
The buggy address belongs to the page:
page:ffffea0004d53500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1354d4
head:ffffea0004d53500 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 0000000600000001 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 0x152a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 2676, ts 717805484086, free_ts 717708570883
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
get_page_from_freelist+0x2cc5/0x2d50 mm/page_alloc.c:4485
__alloc_pages+0x18f/0x440 mm/page_alloc.c:5808
alloc_slab_page mm/slub.c:-1 [inline]
allocate_slab mm/slub.c:1937 [inline]
new_slab+0xa1/0x4d0 mm/slub.c:2000
___slab_alloc+0x381/0x810 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+0x6f2/0x1be0 net/core/neighbour.c:591
__neigh_create+0x31/0x40 net/core/neighbour.c:679
ip6_finish_output2+0xab3/0x1760 net/ipv6/ip6_output.c:127
__ip6_finish_output+0x61e/0x7d0 net/ipv6/ip6_output.c:201
ip6_finish_output+0x31/0x240 net/ipv6/ip6_output.c:211
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1d1/0x3b0 net/ipv6/ip6_output.c:234
dst_output include/net/dst.h:453 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x797/0xc70 net/ipv6/ndisc.c:513
ndisc_send_rs+0x6e5/0x960 net/ipv6/ndisc.c:707
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1472 [inline]
free_pcp_prepare mm/page_alloc.c:1544 [inline]
free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
free_unref_page+0xa2/0x550 mm/page_alloc.c:3616
free_the_page mm/page_alloc.c:805 [inline]
__free_pages+0x6c/0x100 mm/page_alloc.c:5884
free_nonslab_page+0x86/0xc0 mm/slub.c:3564
kfree+0x19a/0x270 mm/slub.c:4585
kvfree+0x35/0x40 mm/util.c:661
bpf_check+0x97b4/0xf280 kernel/bpf/verifier.c:14233
bpf_prog_load+0x1042/0x1550 kernel/bpf/syscall.c:2328
__sys_bpf+0x4c3/0x730 kernel/bpf/syscall.c:4633
__do_sys_bpf kernel/bpf/syscall.c:4737 [inline]
__se_sys_bpf kernel/bpf/syscall.c:4735 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:4735
x64_sys_call+0x4b9/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:322
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:
ffff8881354d5b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881354d5b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881354d5c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881354d5c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881354d5d00: 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: 3695 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 3695 Comm: kworker/u4:2 Tainted: G B W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 00 0b 63 85 e8 3c bc 53 02 0f 0b eb c3 e8 f3 9d 1c ff c6 05 5e ec 99 04 01 48 c7 c7 60 0b 63 85 e8 20 bc 53 02 <0f> 0b eb a7 e8 d7 9d 1c ff c6 05 3f ec 99 04 01 48 c7 c7 a0 0a 63
RSP: 0018:ffffc90000b27c38 EFLAGS: 00010246
RAX: 81cc026075fb6e00 RBX: 0000000000000003 RCX: ffff88814f51e2c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90000b27c48 R08: dffffc0000000000 R09: ffffed103ee265e8
R10: ffffed103ee265e8 R11: 1ffff1103ee265e7 R12: ffff888128f19820
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffffd CR3: 000000012790b000 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_dec_refcount+0xc8/0x1a0 net/l2tp/l2tp_core.c:204
l2tp_session_delete+0x3ab/0x4a0 net/l2tp/l2tp_core.c:1572
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
l2tp_tunnel_del_work+0x1d2/0x3e0 net/l2tp/l2tp_core.c:1258
process_one_work+0x6be/0xba0 kernel/workqueue.c:2325
worker_thread+0xa59/0x1200 kernel/workqueue.c:2472
kthread+0x411/0x500 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
---[ end trace c4e164bc565a3116 ]---