==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff88813372dc00 by task syz.6.957/4472

CPU: 1 PID: 4472 Comm: syz.6.957 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Call Trace:
 <TASK>
 __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_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435
 __sock_release net/socket.c:649 [inline]
 sock_close+0xb8/0x200 net/socket.c:1336
 __fput+0x22b/0x900 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xb70/0x29a0 kernel/exit.c:896
 do_group_exit+0x149/0x310 kernel/exit.c:1010
 get_signal+0x64f/0x1430 kernel/signal.c:2920
 arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:157 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fe7e2b7fb19
Code: Unable to access opcode bytes at RIP 0x7fe7e2b7faef.
RSP: 002b:00007fe7e1553028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: 0000200000000000 RBX: 00007fe7e2e06360 RCX: 00007fe7e2b7fb19
RDX: b635773f06ebbeeb RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007fe7e2c17b70 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe7e2e063f8 R14: 00007fe7e2e06360 R15: 00007ffc3afeca28
 </TASK>

Allocated by task 4468:
 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 45:
 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
 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

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+0xb6/0x860 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_flush_dev+0x667/0x810 net/core/neighbour.c:374
 __neigh_ifdown+0x3f/0x3a0 net/core/neighbour.c:391
 neigh_ifdown+0x1f/0x30 net/core/neighbour.c:408
 rt6_disable_ip+0x7b0/0x840 net/ipv6/route.c:4917
 addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3817
 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:11153
 default_device_exit_batch+0x35e/0x3c0 net/core/dev.c:11710
 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 ffff88813372dc00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff88813372dc00, ffff88813372de00)
The buggy address belongs to the page:
page:ffffea0004cdcb00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13372c
head:ffffea0004cdcb00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004a84300 0000000400000004 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 437, ts 32019535880, free_ts 31087124327
 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]
 kmem_cache_alloc_trace+0x146/0x270 mm/slub.c:3272
 kmem_cache_alloc_node_trace include/linux/slab.h:508 [inline]
 kmalloc_node include/linux/slab.h:637 [inline]
 kzalloc_node include/linux/slab.h:761 [inline]
 alloc_fair_sched_group+0x1ba/0x6d0 kernel/sched/fair.c:11790
 sched_create_group+0x42/0x230 kernel/sched/core.c:10059
 cpu_cgroup_css_alloc+0x18/0x1c0 kernel/sched/core.c:10210
 css_create kernel/cgroup/cgroup.c:5439 [inline]
 cgroup_apply_control_enable+0x37b/0xdb0 kernel/cgroup/cgroup.c:3253
 cgroup_mkdir+0x1171/0x13d0 kernel/cgroup/cgroup.c:5659
 kernfs_iop_mkdir+0x1a3/0x2b0 fs/kernfs/dir.c:1192
 vfs_mkdir+0x38b/0x590 fs/namei.c:4073
 do_mkdirat+0x174/0x4d0 fs/namei.c:4098
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_pages_ok+0xa13/0xae0 mm/page_alloc.c:1777
 free_the_page mm/page_alloc.c:810 [inline]
 __free_pages+0xf6/0x100 mm/page_alloc.c:5905
 free_nonslab_page+0x86/0xc0 mm/slub.c:3564
 kfree+0x19a/0x270 mm/slub.c:4585
 kvfree+0x35/0x40 mm/util.c:661
 kvm_free_memslots virt/kvm/kvm_main.c:951 [inline]
 kvm_destroy_vm virt/kvm/kvm_main.c:1255 [inline]
 kvm_put_kvm+0xf78/0x1190 virt/kvm/kvm_main.c:1284
 kvm_vm_release+0x46/0x50 virt/kvm/kvm_main.c:1307
 __fput+0x22b/0x900 fs/file_table.c:311
 ____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:184
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
 ffff88813372db00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88813372db80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88813372dc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88813372dc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88813372dd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 4472 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 0 PID: 4472 Comm: syz.6.957 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 ec 16 0a fd be 02 00 00 00 eb 0a e8 e0 16 0a fd be 01 00 00 00 4c 89 f7 e8 b3 bc f0 fd e9 0f ff ff ff e8 c9 16 0a fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 b8 16 0a fd 4c 89 f7 be 03
RSP: 0018:ffffc90000ed7890 EFLAGS: 00010293
RAX: ffffffff845fc037 RBX: ffff888116127000 RCX: ffff88810f8d0000
RDX: 0000000000000000 RSI: 0000000011d41660 RDI: 000000000c04eb7d
RBP: ffffc90000ed78b0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e1904c R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000011d41660 R15: ffff88813372dc00
FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555588c99908 CR3: 000000010ee2e000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435
 __sock_release net/socket.c:649 [inline]
 sock_close+0xb8/0x200 net/socket.c:1336
 __fput+0x22b/0x900 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xb70/0x29a0 kernel/exit.c:896
 do_group_exit+0x149/0x310 kernel/exit.c:1010
 get_signal+0x64f/0x1430 kernel/signal.c:2920
 arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:157 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
 __syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fe7e2b7fb19
Code: Unable to access opcode bytes at RIP 0x7fe7e2b7faef.
RSP: 002b:00007fe7e1553028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: 0000200000000000 RBX: 00007fe7e2e06360 RCX: 00007fe7e2b7fb19
RDX: b635773f06ebbeeb RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007fe7e2c17b70 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe7e2e063f8 R14: 00007fe7e2e06360 R15: 00007ffc3afeca28
 </TASK>
---[ end trace b293c0b85a09177b ]---