netlink: 8 bytes leftover after parsing attributes in process `syz.2.111'. ================================================================== BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156 Read of size 4 at addr ffff888115c4ec00 by task syz.2.111/803 CPU: 1 PID: 803 Comm: syz.2.111 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026 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:1287 __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:879 do_group_exit+0x149/0x310 kernel/exit.c:993 get_signal+0xfb1/0x1300 kernel/signal.c:2806 arch_do_signal_or_restart+0xe7/0x11b0 arch/x86/kernel/signal.c:805 handle_signal_work kernel/entry/common.c:148 [inline] exit_to_user_mode_loop+0xa2/0xe0 kernel/entry/common.c:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f573d0d8559 Code: Unable to access opcode bytes at RIP 0x7f573d0d852f. RSP: 002b:00007f573bb300e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca RAX: fffffffffffffe00 RBX: 00007f573d35efa8 RCX: 00007f573d0d8559 RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f573d35efa8 RBP: 00007f573d35efa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f573d35f038 R14: 00007ffd704a0240 R15: 00007ffd704a0328 Allocated by task 803: 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 300: 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 drop_sysctl_table+0x2f5/0x430 fs/proc/proc_sysctl.c:1684 drop_sysctl_table+0x2e4/0x430 fs/proc/proc_sysctl.c:1687 unregister_sysctl_table+0x75/0x120 fs/proc/proc_sysctl.c:1722 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:127 neigh_sysctl_unregister+0x78/0x90 net/core/neighbour.c:3732 devinet_sysctl_unregister net/ipv4/devinet.c:2650 [inline] inetdev_destroy net/ipv4/devinet.c:326 [inline] inetdev_event+0x7df/0x1010 net/ipv4/devinet.c:1612 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] unregister_netdevice_many+0x100e/0x19f0 net/core/dev.c:10778 unregister_netdevice_queue+0x2e1/0x320 net/core/dev.c:10712 unregister_netdevice include/linux/netdevice.h:2939 [inline] __tun_detach+0xc9d/0x1450 drivers/net/tun.c:697 tun_detach drivers/net/tun.c:713 [inline] tun_chr_close+0x92/0x140 drivers/net/tun.c:3500 __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 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:175 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb The buggy address belongs to the object at ffff888115c4ec00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff888115c4ec00, ffff888115c4ee00) The buggy address belongs to the page: page:ffffea0004571300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x115c4c head:ffffea0004571300 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 0000000000000000 0000000100000001 ffff888100043080 raw: 0000000000000000 0000000080100010 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 84, ts 31728809812, free_ts 31685346731 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_track_caller+0x1e4/0x310 mm/slub.c:4541 __kmalloc_reserve net/core/skbuff.c:144 [inline] __alloc_skb+0xdc/0x520 net/core/skbuff.c:212 alloc_skb include/linux/skbuff.h:1126 [inline] alloc_skb_with_frags+0xa3/0x560 net/core/skbuff.c:6055 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2392 unix_dgram_sendmsg+0x6f3/0x18f0 net/unix/af_unix.c:1725 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 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] kmem_cache_alloc+0x15a/0x2d0 mm/slub.c:2965 shmem_alloc_inode+0x1a/0x30 mm/shmem.c:3816 alloc_inode fs/inode.c:233 [inline] new_inode_pseudo+0x62/0x210 fs/inode.c:968 new_inode+0x28/0x1e0 fs/inode.c:997 Memory state around the buggy address: ffff888115c4eb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888115c4eb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff888115c4ec00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888115c4ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888115c4ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ WARNING: CPU: 1 PID: 803 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: 803 Comm: syz.2.111 Tainted: G B syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026 RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156 Code: 5d c3 e8 bc f7 34 fd be 02 00 00 00 eb 0a e8 b0 f7 34 fd be 01 00 00 00 4c 89 f7 e8 33 73 0e fe e9 0f ff ff ff e8 99 f7 34 fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 88 f7 34 fd 4c 89 f7 be 03 RSP: 0018:ffffc90000daf8e0 EFLAGS: 00010293 RAX: ffffffff842fbf27 RBX: ffff8881270cd000 RCX: ffff888115c88000 RDX: 0000000000000000 RSI: 000000000d2d5aa0 RDI: 000000000c04eb7d RBP: ffffc90000daf900 R08: 0000000000000003 R09: 0000000000000004 R10: dffffc0000000000 R11: fffffbfff0dcf848 R12: dffffc0000000000 R13: dffffc0000000000 R14: 000000000d2d5aa0 R15: ffff888115c4ec00 FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005555946ff908 CR3: 000000010e901000 CR4: 00000000003506b0 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:1287 __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:879 do_group_exit+0x149/0x310 kernel/exit.c:993 get_signal+0xfb1/0x1300 kernel/signal.c:2806 arch_do_signal_or_restart+0xe7/0x11b0 arch/x86/kernel/signal.c:805 handle_signal_work kernel/entry/common.c:148 [inline] exit_to_user_mode_loop+0xa2/0xe0 kernel/entry/common.c:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f573d0d8559 Code: Unable to access opcode bytes at RIP 0x7f573d0d852f. RSP: 002b:00007f573bb300e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca RAX: fffffffffffffe00 RBX: 00007f573d35efa8 RCX: 00007f573d0d8559 RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f573d35efa8 RBP: 00007f573d35efa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f573d35f038 R14: 00007ffd704a0240 R15: 00007ffd704a0328 ---[ end trace 7f06bb24a0b66d0e ]---