==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff888131a4b800 by task syz.1.2510/9210

CPU: 0 PID: 9210 Comm: syz.1.2510 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 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
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
 pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:434
 __sock_release net/socket.c:652 [inline]
 sock_close+0xc9/0x220 net/socket.c:1389
 __fput+0x1fd/0x8f0 fs/file_table.c:320
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xaf2/0x2850 kernel/exit.c:887
 do_group_exit+0x21b/0x2e0 kernel/exit.c:1030
 get_signal+0x1382/0x14f0 kernel/signal.c:2891
 arch_do_signal_or_restart+0xd1/0x11c0 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0x87/0xd0 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:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fe95999ce59
Code: Unable to access opcode bytes at 0x7fe95999ce2f.
RSP: 002b:00007fe95a854028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: fffffffffffffe00 RBX: 00007fe959c15fa0 RCX: 00007fe95999ce59
RDX: 0000000000000001 RSI: 0000200000003c00 RDI: 000000000000000c
RBP: 00007fe959a32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000040002002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe959c16038 R14: 00007fe959c15fa0 R15: 00007ffc357cd6d8
 </TASK>

Allocated by task 9210:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:380 [inline]
 __kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
 kasan_kmalloc include/linux/kasan.h:212 [inline]
 __do_kmalloc_node mm/slab_common.c:938 [inline]
 __kmalloc+0xb4/0x1e0 mm/slab_common.c:951
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 l2tp_session_create+0x38/0xbd0 net/l2tp/l2tp_core.c:1609
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:771
 __sys_connect_file net/socket.c:2000 [inline]
 __sys_connect+0x3da/0x460 net/socket.c:2017
 __do_sys_connect net/socket.c:2027 [inline]
 __se_sys_connect net/socket.c:2024 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2024
 x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 9210:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
 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_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
 pppox_ioctl+0x1f6/0x330 drivers/net/ppp/pppox.c:93
 sock_do_ioctl+0x114/0x330 net/socket.c:1191
 sock_ioctl+0x475/0x700 net/socket.c:1310
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0x12f/0x1b0 fs/ioctl.c:856
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:856
 x64_sys_call+0x58b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
 kvfree_call_rcu+0x8b/0x7a0 kernel/rcu/tree.c:3445
 drop_sysctl_table+0x2f5/0x430 fs/proc/proc_sysctl.c:1731
 drop_sysctl_table+0x2e4/0x430 fs/proc/proc_sysctl.c:1734
 unregister_sysctl_table+0x75/0x120 fs/proc/proc_sysctl.c:1769
 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:175
 neigh_sysctl_unregister+0x78/0x90 net/core/neighbour.c:3871
 devinet_sysctl_unregister net/ipv4/devinet.c:2664 [inline]
 inetdev_destroy net/ipv4/devinet.c:329 [inline]
 inetdev_event+0x839/0x10a0 net/ipv4/devinet.c:1615
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
 call_netdevice_notifiers_info net/core/dev.c:2022 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2060 [inline]
 call_netdevice_notifiers net/core/dev.c:2074 [inline]
 unregister_netdevice_many+0x104a/0x1910 net/core/dev.c:11005
 vti6_exit_batch_net+0x273/0x2c0 net/ipv6/ip6_vti.c:1191
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x630/0xb10 net/core/net_namespace.c:604
 process_one_work+0x717/0xc30 kernel/workqueue.c:2302
 worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Second to last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __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+0xcf/0xf50 kernel/rcu/tree.c:2926
 fib6_info_release include/net/ip6_fib.h:350 [inline]
 fib6_del_route net/ipv6/ip6_fib.c:2005 [inline]
 fib6_del+0xbda/0xef0 net/ipv6/ip6_fib.c:2038
 fib6_clean_node+0x2af/0x550 net/ipv6/ip6_fib.c:2200
 fib6_walk_continue+0x55d/0x760 net/ipv6/ip6_fib.c:2122
 fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2170
 fib6_clean_tree net/ipv6/ip6_fib.c:2250 [inline]
 __fib6_clean_all net/ipv6/ip6_fib.c:2266 [inline]
 fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2277
 rt6_sync_down_dev net/ipv6/route.c:4923 [inline]
 rt6_disable_ip+0x123/0x8e0 net/ipv6/route.c:4928
 addrconf_ifdown+0x15d/0x1950 net/ipv6/addrconf.c:3824
 addrconf_notify+0x39f/0xe30 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
 call_netdevice_notifiers_info net/core/dev.c:2022 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2060 [inline]
 call_netdevice_notifiers net/core/dev.c:2074 [inline]
 __dev_notify_flags+0x276/0x5b0 net/core/dev.c:8732
 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8768
 do_setlink+0xc02/0x2a10 net/core/rtnetlink.c:2836
 rtnl_group_changelink net/core/rtnetlink.c:3364 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3621 [inline]
 rtnl_newlink+0x10b3/0x20d0 net/core/rtnetlink.c:3658
 rtnetlink_rcv_msg+0xb28/0xde0 net/core/rtnetlink.c:6153
 netlink_rcv_skb+0x200/0x450 net/netlink/af_netlink.c:2521
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6171
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x8c1/0xa60 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x8b9/0xbd0 net/netlink/af_netlink.c:1873
 sock_sendmsg_nosec net/socket.c:716 [inline]
 __sock_sendmsg net/socket.c:728 [inline]
 ____sys_sendmsg+0x5fb/0x9c0 net/socket.c:2508
 ___sys_sendmsg+0x2a2/0x360 net/socket.c:2562
 __sys_sendmsg net/socket.c:2591 [inline]
 __do_sys_sendmsg net/socket.c:2600 [inline]
 __se_sys_sendmsg net/socket.c:2598 [inline]
 __x64_sys_sendmsg+0x20d/0x2e0 net/socket.c:2598
 x64_sys_call+0x171/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888131a4b800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff888131a4b800, ffff888131a4ba00)

The buggy address belongs to the physical page:
page:ffffea0004c69200 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888131a4bc00 pfn:0x131a48
head:ffffea0004c69200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004cb8a08 ffffea0004cb8808 ffff888100042f00
raw: ffff888131a4bc00 000000000010000e 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 287, tgid 287 (syz-executor), ts 22756664545, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2672
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2679
 get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4586
 __alloc_pages+0x1fa/0x610 mm/page_alloc.c:5930
 alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1967 [inline]
 new_slab+0x98/0x3e0 mm/slub.c:2020
 ___slab_alloc+0x70f/0xb70 mm/slub.c:3177
 __slab_alloc+0x5e/0xa0 mm/slub.c:3263
 slab_alloc_node mm/slub.c:3348 [inline]
 __kmem_cache_alloc_node+0x204/0x2d0 mm/slub.c:3423
 __do_kmalloc_node mm/slab_common.c:937 [inline]
 __kmalloc_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
 kmalloc_reserve net/core/skbuff.c:449 [inline]
 __alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
 alloc_skb include/linux/skbuff.h:1322 [inline]
 nlmsg_new include/net/netlink.h:987 [inline]
 inet_netconf_notify_devconf+0x169/0x220 net/ipv4/devinet.c:2128
 __devinet_sysctl_register+0x2af/0x320 net/ipv4/devinet.c:2618
 devinet_sysctl_register+0x169/0x1e0 net/ipv4/devinet.c:2652
 inetdev_init+0x2ca/0x510 net/ipv4/devinet.c:280
 inetdev_event+0x1f4/0x10a0 net/ipv4/devinet.c:1547
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888131a4b700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888131a4b780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888131a4b800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888131a4b880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888131a4b900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 9210 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 1 PID: 9210 Comm: syz.1.2510 Tainted: G    B              syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 ac c1 d5 fc be 02 00 00 00 eb 0a e8 a0 c1 d5 fc be 01 00 00 00 4c 89 f7 e8 73 20 cd fd e9 0f ff ff ff e8 89 c1 d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 78 c1 d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc900015ef7f0 EFLAGS: 00010293
RAX: ffffffff849ba2a7 RBX: ffff88811382c000 RCX: ffff88812300d100
RDX: 0000000000000000 RSI: 000000003147af70 RDI: 000000000c04eb7d
RBP: ffffc900015ef810 R08: ffffffff87b757e7 R09: 1ffffffff0f6eafc
R10: dffffc0000000000 R11: fffffbfff0f6eafd R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000003147af70 R15: ffff888131a4b800
FS:  0000000000000000(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f444e0120b8 CR3: 000000012ef4c000 CR4: 00000000003506a0
Call Trace:
 <TASK>
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:434
 __sock_release net/socket.c:652 [inline]
 sock_close+0xc9/0x220 net/socket.c:1389
 __fput+0x1fd/0x8f0 fs/file_table.c:320
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xaf2/0x2850 kernel/exit.c:887
 do_group_exit+0x21b/0x2e0 kernel/exit.c:1030
 get_signal+0x1382/0x14f0 kernel/signal.c:2891
 arch_do_signal_or_restart+0xd1/0x11c0 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0x87/0xd0 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:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fe95999ce59
Code: Unable to access opcode bytes at 0x7fe95999ce2f.
RSP: 002b:00007fe95a854028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: fffffffffffffe00 RBX: 00007fe959c15fa0 RCX: 00007fe95999ce59
RDX: 0000000000000001 RSI: 0000200000003c00 RDI: 000000000000000c
RBP: 00007fe959a32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000040002002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe959c16038 R14: 00007fe959c15fa0 R15: 00007ffc357cd6d8
 </TASK>
---[ end trace 0000000000000000 ]---