==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff888133c63800 by task syz.8.2309/8945

CPU: 0 PID: 8945 Comm: syz.8.2309 Tainted: G        W          syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 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
 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+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: 0033:0x7f0128f9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd60fff9f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffd60fffae0 RCX: 00007f0128f9e0d9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000053d13 R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b33a20000 R11: 0000000000000246 R12: 00007ffd60fffb20
R13: 00007f0129225fac R14: 0000000000053d7c R15: 00007f0129225fa0
 </TASK>

Allocated by task 8946:
 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 6069:
 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
 l2tp_session_delete+0x3df/0x4d0 net/l2tp/l2tp_core.c:1582
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1228 [inline]
 l2tp_tunnel_del_work+0x199/0x410 net/l2tp/l2tp_core.c:1266
 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

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]
 ip6_route_info_create+0xaa8/0x14d0 net/ipv6/route.c:3878
 ip6_route_add+0x27/0x130 net/ipv6/route.c:3892
 addrconf_add_mroute net/ipv6/addrconf.c:2530 [inline]
 addrconf_add_dev+0x388/0x4a0 net/ipv6/addrconf.c:2548
 inet6_addr_add+0x1a8/0x9c0 net/ipv6/addrconf.c:3007
 inet6_rtm_newaddr+0x74a/0xa10 net/ipv6/addrconf.c:4999
 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_sendto+0x4ac/0x660 net/socket.c:2142
 __do_sys_sendto net/socket.c:2154 [inline]
 __se_sys_sendto net/socket.c:2150 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2150
 x64_sys_call+0x83/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 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 ffff888133c63800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff888133c63800, ffff888133c63a00)

The buggy address belongs to the physical page:
page:ffffea0004cf1800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x133c60
head:ffffea0004cf1800 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 287, tgid 287 (syz-executor), ts 24273989921, free_ts 24273741605
 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+0xa4/0x1e0 mm/slab_common.c:951
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:156
 ip6_route_info_create+0x51b/0x14d0 net/ipv6/route.c:3796
 addrconf_f6i_alloc+0x19c/0x3f0 net/ipv6/route.c:4600
 fixup_permanent_addr net/ipv6/addrconf.c:3554 [inline]
 addrconf_permanent_addr+0x237/0x940 net/ipv6/addrconf.c:3593
 addrconf_notify+0x7ca/0xe30 net/ipv6/addrconf.c:3665
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1580 [inline]
 free_pcp_prepare mm/page_alloc.c:1654 [inline]
 free_unref_page_prepare+0x80c/0x820 mm/page_alloc.c:3621
 free_unref_page+0x93/0x530 mm/page_alloc.c:3719
 free_the_page mm/page_alloc.c:863 [inline]
 __free_pages+0x67/0x100 mm/page_alloc.c:6020
 free_pages+0x82/0x90 mm/page_alloc.c:6031
 __stack_depot_save+0x45f/0x490 lib/stackdepot.c:506
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_set_track+0x60/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 __kasan_slab_alloc+0x72/0x80 mm/kasan/common.c:334
 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+0x179/0x330 mm/slub.c:3429
 __alloc_skb+0xe8/0x4a0 net/core/skbuff.c:508
 alloc_skb include/linux/skbuff.h:1322 [inline]
 wg_packet_send_keepalive+0x62/0x1c0 drivers/net/wireguard/send.c:226
 wg_open+0x214/0x300 drivers/net/wireguard/device.c:56
 __dev_open+0x39c/0x520 net/core/dev.c:1509
 __dev_change_flags+0x1f2/0x6b0 net/core/dev.c:8692
 dev_change_flags+0x80/0x1a0 net/core/dev.c:8763

Memory state around the buggy address:
 ffff888133c63700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888133c63780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888133c63800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888133c63880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888133c63900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 8945 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: 8945 Comm: syz.8.2309 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 5c b3 d5 fc be 02 00 00 00 eb 0a e8 50 b3 d5 fc be 01 00 00 00 4c 89 f7 e8 23 18 cd fd e9 0f ff ff ff e8 39 b3 d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 28 b3 d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc900007cfcb0 EFLAGS: 00010293
RAX: ffffffff849bb307 RBX: ffff88810d859000 RCX: ffff88811dcebcc0
RDX: 0000000000000000 RSI: 0000000011cf9990 RDI: 000000000c04eb7d
RBP: ffffc900007cfcd0 R08: ffffffff87b757e7 R09: 1ffffffff0f6eafc
R10: dffffc0000000000 R11: fffffbfff0f6eafd R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000011cf9990 R15: ffff888133c63800
FS:  000055555d2c5500(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe270fef2f8 CR3: 00000001273ef000 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
 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+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: 0033:0x7f0128f9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd60fff9f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffd60fffae0 RCX: 00007f0128f9e0d9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000053d13 R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b33a20000 R11: 0000000000000246 R12: 00007ffd60fffb20
R13: 00007f0129225fac R14: 0000000000053d7c R15: 00007f0129225fa0
 </TASK>
---[ end trace 0000000000000000 ]---