================================================================== BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156 Read of size 4 at addr ffff888127f27c00 by task syz.0.233/1208 CPU: 0 PID: 1208 Comm: syz.0.233 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Call Trace: __dump_stack+0x21/0x24 lib/dump_stack.c:77 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248 __kasan_report mm/kasan/report.c:435 [inline] kasan_report+0x100/0x140 mm/kasan/report.c:452 __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:597 [inline] sock_close+0xb8/0x200 net/socket.c:1286 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 exit_task_work include/linux/task_work.h:33 [inline] do_exit+0xa7c/0x24e0 kernel/exit.c:873 do_group_exit+0x149/0x310 kernel/exit.c:987 __do_sys_exit_group kernel/exit.c:998 [inline] __se_sys_exit_group kernel/exit.c:996 [inline] __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:996 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7ff8483e8e59 Code: Unable to access opcode bytes at RIP 0x7ff8483e8e2f. RSP: 002b:00007ffff5f7d6c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff8483e8e59 RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007ffff5f7d72c R08: 0000000000000000 R09: 00000000000927c0 R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000000027 R13: 00000000000927c0 R14: 000000000000d302 R15: 00007ffff5f7d780 Allocated by task 1210: 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:430 [inline] ____kasan_kmalloc mm/kasan/common.c:509 [inline] __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518 kasan_kmalloc include/linux/kasan.h:254 [inline] __kmalloc+0x19f/0x330 mm/slub.c:4038 kmalloc include/linux/slab.h:560 [inline] kzalloc include/linux/slab.h:667 [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:1866 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1883 __do_sys_connect net/socket.c:1893 [inline] __se_sys_connect net/socket.c:1890 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1890 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 9: 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:362 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370 kasan_slab_free include/linux/kasan.h:220 [inline] slab_free_hook mm/slub.c:1600 [inline] slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626 slab_free mm/slub.c:3208 [inline] kfree+0xc0/0x270 mm/slub.c:4196 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline] l2tp_session_put+0xb2/0x1a0 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+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 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+0x117/0x670 kernel/rcu/tree.c:3539 inet6_ifa_finish_destroy+0x129/0x1b0 net/ipv6/addrconf.c:1001 in6_ifa_put include/net/addrconf.h:459 [inline] addrconf_ifdown+0x121c/0x1890 net/ipv6/addrconf.c:3924 addrconf_notify+0x3bd/0xea0 net/ipv6/addrconf.c:-1 notifier_call_chain kernel/notifier.c:83 [inline] raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410 call_netdevice_notifiers_info net/core/dev.c:2054 [inline] call_netdevice_notifiers_extack net/core/dev.c:2066 [inline] call_netdevice_notifiers net/core/dev.c:2080 [inline] dev_close_many+0x328/0x4d0 net/core/dev.c:1655 unregister_netdevice_many+0x477/0x19f0 net/core/dev.c:10757 vti6_exit_batch_net+0x273/0x2c0 net/ipv6/ip6_vti.c:1186 ops_exit_list net/core/net_namespace.c:190 [inline] cleanup_net+0x5fe/0xb80 net/core/net_namespace.c:609 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 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 insert_work+0x51/0x320 kernel/workqueue.c:1352 __queue_work+0x91f/0xca0 kernel/workqueue.c:1518 __queue_delayed_work+0x188/0x200 kernel/workqueue.c:1672 mod_delayed_work_on+0x7b/0xd0 kernel/workqueue.c:1746 mod_delayed_work include/linux/workqueue.h:545 [inline] addrconf_mod_dad_work+0x7d/0x120 net/ipv6/addrconf.c:333 addrconf_dad_start net/ipv6/addrconf.c:4104 [inline] addrconf_add_linklocal+0x47d/0x660 net/ipv6/addrconf.c:3261 addrconf_addr_gen+0x53f/0x6a0 net/ipv6/addrconf.c:3388 addrconf_dev_config+0x299/0x510 net/ipv6/addrconf.c:3440 addrconf_notify+0x9d8/0xea0 net/ipv6/addrconf.c:3673 notifier_call_chain kernel/notifier.c:83 [inline] raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410 call_netdevice_notifiers_info net/core/dev.c:2054 [inline] call_netdevice_notifiers_extack net/core/dev.c:2066 [inline] call_netdevice_notifiers net/core/dev.c:2080 [inline] __dev_notify_flags+0x2f4/0x5b0 net/core/dev.c:8585 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8623 do_setlink+0xb19/0x29a0 net/core/rtnetlink.c:2736 __rtnl_newlink net/core/rtnetlink.c:3414 [inline] rtnl_newlink+0x13e6/0x1830 net/core/rtnetlink.c:3534 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5614 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2503 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5632 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] netlink_unicast+0x86c/0xa30 net/netlink/af_netlink.c:1340 netlink_sendmsg+0x949/0xb70 net/netlink/af_netlink.c:1914 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] __sys_sendto+0x467/0x620 net/socket.c:2006 __do_sys_sendto net/socket.c:2018 [inline] __se_sys_sendto net/socket.c:2014 [inline] __x64_sys_sendto+0xe5/0x100 net/socket.c:2014 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb The buggy address belongs to the object at ffff888127f27c00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff888127f27c00, ffff888127f27e00) The buggy address belongs to the page: page:ffffea00049fc900 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x127f24 head:ffffea00049fc900 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 279, ts 23972314435, free_ts 0 set_page_owner include/linux/page_owner.h:35 [inline] post_alloc_hook mm/page_alloc.c:2456 [inline] prep_new_page+0x176/0x190 mm/page_alloc.c:2462 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384 alloc_slab_page mm/slub.c:-1 [inline] allocate_slab mm/slub.c:1813 [inline] new_slab+0x84/0x3f0 mm/slub.c:1874 new_slab_objects mm/slub.c:2632 [inline] ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796 __slab_alloc+0x63/0xa0 mm/slub.c:2836 slab_alloc_node mm/slub.c:2918 [inline] slab_alloc mm/slub.c:2960 [inline] __kmalloc+0x1f9/0x330 mm/slub.c:4034 __kmalloc_node include/linux/slab.h:421 [inline] kmalloc_node include/linux/slab.h:578 [inline] kzalloc_node include/linux/slab.h:678 [inline] qdisc_alloc+0x79/0x720 net/sched/sch_generic.c:864 qdisc_create_dflt+0x6b/0x390 net/sched/sch_generic.c:927 attach_one_default_qdisc net/sched/sch_generic.c:1090 [inline] netdev_for_each_tx_queue include/linux/netdevice.h:2321 [inline] attach_default_qdiscs net/sched/sch_generic.c:1108 [inline] dev_activate+0x292/0x11c0 net/sched/sch_generic.c:1167 __dev_open+0x3e9/0x500 net/core/dev.c:1551 __dev_change_flags+0x1e4/0x6a0 net/core/dev.c:8547 dev_change_flags+0x80/0x1a0 net/core/dev.c:8618 do_setlink+0xb19/0x29a0 net/core/rtnetlink.c:2736 __rtnl_newlink net/core/rtnetlink.c:3414 [inline] rtnl_newlink+0x13e6/0x1830 net/core/rtnetlink.c:3534 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5614 page_owner free stack trace missing Memory state around the buggy address: ffff888127f27b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888127f27b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff888127f27c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888127f27c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888127f27d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ WARNING: CPU: 1 PID: 1208 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: 1208 Comm: syz.0.233 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 fc 0b 36 fd be 02 00 00 00 eb 0a e8 f0 0b 36 fd be 01 00 00 00 4c 89 f7 e8 a3 76 0f fe e9 0f ff ff ff e8 d9 0b 36 fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 c8 0b 36 fd 4c 89 f7 be 03 RSP: 0018:ffffc90000b57c00 EFLAGS: 00010293 RAX: ffffffff842e9627 RBX: ffff888128eac800 RCX: ffff88811ad613c0 RDX: 0000000000000000 RSI: 000000000ae7c780 RDI: 000000000c04eb7d RBP: ffffc90000b57c20 R08: 0000000000000003 R09: 0000000000000004 R10: dffffc0000000000 R11: fffffbfff0dcf648 R12: dffffc0000000000 R13: dffffc0000000000 R14: 000000000ae7c780 R15: ffff888127f27c00 FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fc155d27000 CR3: 000000012560f000 CR4: 00000000003506a0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435 __sock_release net/socket.c:597 [inline] sock_close+0xb8/0x200 net/socket.c:1286 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 exit_task_work include/linux/task_work.h:33 [inline] do_exit+0xa7c/0x24e0 kernel/exit.c:873 do_group_exit+0x149/0x310 kernel/exit.c:987 __do_sys_exit_group kernel/exit.c:998 [inline] __se_sys_exit_group kernel/exit.c:996 [inline] __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:996 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7ff8483e8e59 Code: Unable to access opcode bytes at RIP 0x7ff8483e8e2f. RSP: 002b:00007ffff5f7d6c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff8483e8e59 RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007ffff5f7d72c R08: 0000000000000000 R09: 00000000000927c0 R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000000027 R13: 00000000000927c0 R14: 000000000000d302 R15: 00007ffff5f7d780 ---[ end trace 34e3f607d54c7888 ]---