==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff888129491c00 by task syz.5.3137/10758

CPU: 0 PID: 10758 Comm: syz.5.3137 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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:890
 __do_sys_exit kernel/exit.c:973 [inline]
 __se_sys_exit kernel/exit.c:971 [inline]
 __x64_sys_exit+0x40/0x40 kernel/exit.c:971
 x64_sys_call+0x44/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
 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
RIP: 0033:0x7f5e5aadd0d9
Code: Unable to access opcode bytes at RIP 0x7f5e5aadd0af.
RSP: 002b:00007f5e59514ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f5e5aadd0d9
RDX: 00007f5e595159c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f5e5ab74024 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5e5ad65128 R14: 00007f5e5ad65090 R15: 00007ffe5d5fe6c8
 </TASK>

Allocated by task 10756:
 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 8680:
 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
 drop_sysctl_table+0x2f5/0x430 fs/proc/proc_sysctl.c:1687
 drop_sysctl_table+0x2e4/0x430 fs/proc/proc_sysctl.c:1690
 unregister_sysctl_table+0x7a/0x120 fs/proc/proc_sysctl.c:1725
 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:175
 __devinet_sysctl_unregister net/ipv4/devinet.c:2627 [inline]
 devinet_sysctl_unregister net/ipv4/devinet.c:2655 [inline]
 inetdev_destroy net/ipv4/devinet.c:327 [inline]
 inetdev_event+0x788/0x1060 net/ipv4/devinet.c:1612
 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]
 unregister_netdevice_many+0x103d/0x1a00 net/core/dev.c:11176
 vti6_exit_batch_net+0x273/0x2c0 net/ipv6/ip6_vti.c:1202
 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

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
 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+0x115/0x730 net/ipv6/route.c:4911
 addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3802
 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
 default_device_exit_batch+0x35e/0x3c0 net/core/dev.c:11709
 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 ffff888129491c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff888129491c00, ffff888129491e00)
The buggy address belongs to the page:
page:ffffea0004a52400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x129490
head:ffffea0004a52400 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 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 0x52a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 45, ts 23126646015, 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+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 net/ipv6/addrconf.c:2471 [inline]
 addrconf_add_linklocal+0x3cd/0x660 net/ipv6/addrconf.c:3267
 addrconf_addr_gen+0x53f/0x6a0 net/ipv6/addrconf.c:3396
 addrconf_dev_config net/ipv6/addrconf.c:3441 [inline]
 addrconf_init_auto_addrs+0x867/0xbd0 net/ipv6/addrconf.c:3520
 addrconf_notify+0x95d/0xe00 net/ipv6/addrconf.c:3689
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888129491b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888129491b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888129491c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888129491c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888129491d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 10758 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: 10758 Comm: syz.5.3137 Tainted: G    B   W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 2c 83 0b fd be 02 00 00 00 eb 0a e8 20 83 0b fd be 01 00 00 00 4c 89 f7 e8 33 02 f2 fd e9 0f ff ff ff e8 09 83 0b fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 f8 82 0b fd 4c 89 f7 be 03
RSP: 0018:ffffc90001217bf0 EFLAGS: 00010293
RAX: ffffffff845e33d7 RBX: ffff8881160e6000 RCX: ffff888106b962c0
RDX: 0000000000000000 RSI: 0000000026858960 RDI: 000000000c04eb7d
RBP: ffffc90001217c10 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e18e4c R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000026858960 R15: ffff888129491c00
FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555720df908 CR3: 000000010cb5c000 CR4: 00000000003506b0
DR0: 0000000000000008 DR1: 0000000000000002 DR2: 0000000000000404
DR3: ffffffffefffff14 DR6: 00000000ffff0ff0 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:890
 __do_sys_exit kernel/exit.c:973 [inline]
 __se_sys_exit kernel/exit.c:971 [inline]
 __x64_sys_exit+0x40/0x40 kernel/exit.c:971
 x64_sys_call+0x44/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
 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
RIP: 0033:0x7f5e5aadd0d9
Code: Unable to access opcode bytes at RIP 0x7f5e5aadd0af.
RSP: 002b:00007f5e59514ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f5e5aadd0d9
RDX: 00007f5e595159c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f5e5ab74024 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5e5ad65128 R14: 00007f5e5ad65090 R15: 00007ffe5d5fe6c8
 </TASK>
---[ end trace 13958c3d330e1270 ]---