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BUG: KASAN: slab-use-after-free in string+0x216/0x2d0
Read of size 1 at addr ffff88810943cdc0 by task syz.2.4528/28586

CPU: 0 UID: 0 PID: 28586 Comm: syz.2.4528 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150
 print_address_description+0x55/0x1e0
 print_report+0x58/0x70
 kasan_report+0x117/0x150
 string+0x216/0x2d0
 vsnprintf+0x74a/0xef0
 vprintk_store+0x3a1/0xd90
 vprintk_emit+0x192/0x560
 _printk+0xdd/0x130
 __setup_irq+0x1015/0x2100
 request_threaded_irq+0x2c1/0x3a0
 pcl816_attach+0x19a/0xa70
 comedi_device_attach+0x52d/0x720
 comedi_unlocked_ioctl+0x8ef/0x1af0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3b2719e0d9
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:00007f3b280e0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3b27425fa0 RCX: 00007f3b2719e0d9
RDX: 00002000000000c0 RSI: 0000000040946400 RDI: 0000000000000003
RBP: 00007f3b27235024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3b27426038 R14: 00007f3b27425fa0 R15: 00007ffdf30188e8
 </TASK>

Allocated by task 27317:
 kasan_save_track+0x3e/0x80
 __kasan_kmalloc+0x93/0xb0
 __kmalloc_node_track_caller_noprof+0x4c3/0x730
 kvasprintf+0xeb/0x1a0
 kobject_set_name_vargs+0x61/0x110
 kobject_init_and_add+0xee/0x1a0
 netdev_queue_update_kobjects+0x249/0x6b0
 netdev_register_kobject+0x258/0x310
 register_netdevice+0x1433/0x1eb0
 veth_newlink+0x49f/0xb70
 rtnl_newlink_create+0x310/0xb00
 rtnl_newlink+0x167f/0x1bd0
 rtnetlink_rcv_msg+0x802/0xc00
 netlink_rcv_skb+0x226/0x4a0
 netlink_unicast+0x7bb/0x940
 netlink_sendmsg+0x813/0xb40
 sock_sendmsg_nosec+0x13a/0x180
 __sys_sendto+0x408/0x5a0
 __x64_sys_sendto+0xde/0x100
 do_syscall_64+0x174/0x580
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5653:
 kasan_save_track+0x3e/0x80
 kasan_save_free_info+0x40/0x50
 __kasan_slab_free+0x5c/0x80
 kfree+0x1c5/0x640
 kobject_put+0x267/0x550
 netdev_queue_update_kobjects+0x5c9/0x6b0
 netdev_unregister_kobject+0x10b/0x450
 unregister_netdevice_many_notify+0x1be4/0x2150
 default_device_exit_batch+0x961/0x9e0
 ops_undo_list+0x4b4/0x8d0
 cleanup_net+0x572/0x810
 process_scheduled_works+0xa8e/0x14e0
 worker_thread+0xa47/0xfb0
 kthread+0x388/0x470
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30

The buggy address belongs to the object at ffff88810943cdc0
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 freed 8-byte region [ffff88810943cdc0, ffff88810943cdc8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88810943cea0 pfn:0x10943c
flags: 0x17ff00000000200(workingset|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000200 ffff888100041500 ffffea00040ec450 ffffea000411b450
raw: ffff88810943cea0 0000000800800072 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 4941527688
 post_alloc_hook+0x1f9/0x250
 get_page_from_freelist+0x2205/0x2280
 __alloc_frozen_pages_noprof+0x217/0x5a0
 allocate_slab+0x7c/0x5e0
 refill_objects+0x2d5/0x350
 __pcs_replace_empty_main+0x2bf/0x6b0
 __kmalloc_node_track_caller_noprof+0x557/0x730
 kstrdup+0x42/0x100
 __kernfs_new_node+0xa9/0x980
 kernfs_create_dir_ns+0xfe/0x230
 sysfs_create_dir_ns+0x12f/0x2a0
 kobject_add_internal+0x622/0xcd0
 kobject_add+0x163/0x240
 device_add+0x3fa/0xb80
 tty_register_device_attr+0x422/0x950
 tty_register_driver+0x82c/0xdf0
page last free pid 82 tgid 82 ts 4941185520 stack trace:
 __free_frozen_pages+0xc8f/0xd80
 __kasan_populate_vmalloc+0x1a8/0x1c0
 alloc_vmap_area+0xd1a/0x1420
 __get_vm_area_node+0x1f2/0x300
 __vmalloc_node_range_noprof+0x343/0x1540
 __vmalloc_node_noprof+0xc2/0x100
 dup_task_struct+0x2ae/0x8c0
 copy_process+0x820/0x4390
 kernel_clone+0x2d7/0x940
 user_mode_thread+0x110/0x180
 call_usermodehelper_exec_work+0x5c/0x230
 process_scheduled_works+0xa8e/0x14e0
 worker_thread+0xa47/0xfb0
 kthread+0x388/0x470
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30

Memory state around the buggy address:
 ffff88810943cc80: fa fc fc fc 06 fc fc fc fa fc fc fc 05 fc fc fc
 ffff88810943cd00: fa fc fc fc 06 fc fc fc fa fc fc fc fa fc fc fc
>ffff88810943cd80: fa fc fc fc 05 fc fc fc fa fc fc fc fa fc fc fc
                                           ^
 ffff88810943ce00: fa fc fc fc fa fc fc fc fa fc fc fc fa fc fc fc
 ffff88810943ce80: fa fc fc fc fa fc fc fc 04 fc fc fc 00 fc fc fc
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