================================================================== BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:808 [inline] BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:865 [inline] BUG: KASAN: use-after-free in l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline] BUG: KASAN: use-after-free in l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273 Read of size 8 at addr ffff88810c12b480 by task kworker/u4:5/816 CPU: 0 PID: 816 Comm: kworker/u4:5 Tainted: G W syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Workqueue: l2tp l2tp_tunnel_del_work 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_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309 hlist_unhashed include/linux/list.h:808 [inline] hlist_del_init include/linux/list.h:865 [inline] l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline] l2tp_tunnel_del_work+0xcd/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 Allocated by task 1457: 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:1867 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1884 __do_sys_connect net/socket.c:1894 [inline] __se_sys_connect net/socket.c:1891 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1891 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 1458: 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 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1 pppox_ioctl+0x1e4/0x320 drivers/net/ppp/pppox.c:93 sock_do_ioctl+0xda/0x380 net/socket.c:1068 sock_ioctl+0x472/0x740 net/socket.c:1208 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:739 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:739 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb 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 kernel/rcu/tree.c:2980 [inline] call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054 fib6_info_release include/net/ip6_fib.h:346 [inline] fixup_permanent_addr net/ipv6/addrconf.c:3514 [inline] addrconf_permanent_addr+0x302/0x940 net/ipv6/addrconf.c:3542 addrconf_notify+0x752/0xea0 net/ipv6/addrconf.c:3610 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:2052 [inline] call_netdevice_notifiers_extack net/core/dev.c:2064 [inline] call_netdevice_notifiers net/core/dev.c:2078 [inline] __dev_notify_flags+0x2f4/0x5b0 net/core/dev.c:8583 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8621 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:2508 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:1919 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] __sys_sendto+0x467/0x620 net/socket.c:2007 __do_sys_sendto net/socket.c:2019 [inline] __se_sys_sendto net/socket.c:2015 [inline] __x64_sys_sendto+0xe5/0x100 net/socket.c:2015 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 ffff88810c12b400 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 128 bytes inside of 512-byte region [ffff88810c12b400, ffff88810c12b600) The buggy address belongs to the page: page:ffffea0004304a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10c128 head:ffffea0004304a00 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 ffffea0004319600 0000000300000003 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 288, ts 20489231084, free_ts 20488251854 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] kmem_cache_alloc_trace+0x1a8/0x2e0 mm/slub.c:2977 kmalloc include/linux/slab.h:555 [inline] kmalloc_array include/linux/slab.h:594 [inline] rtnl_newlink+0x14b/0x1830 net/core/rtnetlink.c:3530 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5614 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2508 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:1919 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] __sys_sendto+0x467/0x620 net/socket.c:2007 __do_sys_sendto net/socket.c:2019 [inline] __se_sys_sendto net/socket.c:2015 [inline] __x64_sys_sendto+0xe5/0x100 net/socket.c:2015 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 page last free stack trace: reset_page_owner include/linux/page_owner.h:28 [inline] free_pages_prepare mm/page_alloc.c:1349 [inline] __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629 free_the_page mm/page_alloc.c:5445 [inline] __free_pages+0xd8/0x390 mm/page_alloc.c:5454 __free_slab+0xcf/0x190 mm/slub.c:1899 free_slab mm/slub.c:1914 [inline] discard_slab mm/slub.c:1920 [inline] unfreeze_partials+0x150/0x180 mm/slub.c:2415 put_cpu_partial+0xc1/0x180 mm/slub.c:2451 __slab_free+0x2c9/0x3a0 mm/slub.c:3100 do_slab_free mm/slub.c:3196 [inline] ___cache_free+0x10e/0x130 mm/slub.c:3215 qlink_free+0x50/0x90 mm/kasan/quarantine.c:157 qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176 kasan_quarantine_reduce+0x14a/0x160 mm/kasan/quarantine.c:283 __kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:440 kasan_slab_alloc include/linux/kasan.h:244 [inline] slab_post_alloc_hook+0x5d/0x2f0 mm/slab.h:580 slab_alloc_node mm/slub.c:2952 [inline] slab_alloc mm/slub.c:2960 [inline] __kmalloc+0x17b/0x330 mm/slub.c:4034 kmalloc include/linux/slab.h:560 [inline] kzalloc include/linux/slab.h:667 [inline] fib_create_info+0x8eb/0x1ed0 net/ipv4/fib_semantics.c:1477 fib_table_insert+0xc2/0x1d50 net/ipv4/fib_trie.c:1170 fib_magic net/ipv4/fib_frontend.c:1107 [inline] fib_add_ifaddr+0xbe3/0xf90 net/ipv4/fib_frontend.c:1153 Memory state around the buggy address: ffff88810c12b380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88810c12b400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff88810c12b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88810c12b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88810c12b580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 1 PID: 816 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28 Modules linked in: CPU: 0 PID: 816 Comm: kworker/u4:5 Tainted: G B W syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Workqueue: l2tp l2tp_tunnel_del_work RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28 Code: 04 01 48 c7 c7 e0 48 40 85 e8 7c ca 3a 02 0f 0b eb c3 e8 73 89 26 ff c6 05 b1 75 82 04 01 48 c7 c7 40 49 40 85 e8 60 ca 3a 02 <0f> 0b eb a7 e8 57 89 26 ff c6 05 92 75 82 04 01 48 c7 c7 60 48 40 RSP: 0018:ffffc9000140fc58 EFLAGS: 00010246 RAX: 0f100141cd8bf100 RBX: 0000000000000003 RCX: ffff888118812780 RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000 RBP: ffffc9000140fc68 R08: ffff8881f7152fbf R09: 1ffff1103ee2a5f7 R10: dffffc0000000000 R11: ffffed103ee2a5f8 R12: ffff888118ade020 R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fa39f0d50bd CR3: 000000011fb56000 CR4: 00000000003506a0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __refcount_sub_and_test include/linux/refcount.h:283 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] l2tp_session_put+0xcb/0x1a0 net/l2tp/l2tp_core.c:192 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 ---[ end trace 9712973239f94399 ]--- device bridge_slave_1 left promiscuous mode bridge0: port 2(bridge_slave_1) entered disabled state device bridge_slave_0 left promiscuous mode bridge0: port 1(bridge_slave_0) entered disabled state device veth1_macvtap left promiscuous mode device veth0_vlan left promiscuous mode