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BUG: KASAN: use-after-free in __mutex_lock+0x812/0x1300
Read of size 8 at addr ffff88810568c0a8 by task khidpd_00020006/25821

CPU: 0 UID: 0 PID: 25821 Comm: khidpd_00020006 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_report+0xba/0x230
 kasan_report+0x117/0x150
 __mutex_lock+0x812/0x1300
 l2cap_unregister_user+0x6a/0x1b0
 hidp_session_thread+0x3cb/0x440
 kthread+0x726/0x8b0
 ret_from_fork+0x51b/0xa40
 ret_from_fork_asm+0x1a/0x30
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88810568fa80 pfn:0x10568c
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
raw: 017ff00000000000 ffffea00042b3f08 ffff888121040d40 0000000000000000
raw: ffff88810568fa80 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x140dc0(GFP_USER|__GFP_ZERO|__GFP_COMP), pid 23615, tgid 23615 (syz-executor), ts 663468344114, free_ts 754248271695
 post_alloc_hook+0x231/0x280
 get_page_from_freelist+0x24dc/0x2580
 __alloc_frozen_pages_noprof+0x18d/0x380
 alloc_pages_mpol+0x232/0x4a0
 ___kmalloc_large_node+0x4e/0x150
 __kmalloc_large_node_noprof+0x18/0x90
 __kmalloc_noprof+0x4b8/0x7e0
 hci_alloc_dev_priv+0x28/0x2060
 vhci_create_device+0x120/0x650
 vhci_write+0x3ce/0x4a0
 vfs_write+0x61d/0xb90
 ksys_write+0x150/0x270
 do_syscall_64+0xe2/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 25795 tgid 25795 stack trace:
 __free_frozen_pages+0xbb9/0xd10
 bt_host_release+0x82/0x90
 device_release+0x9e/0x1d0
 kobject_put+0x228/0x560
 vhci_release+0x15a/0x1a0
 __fput+0x44f/0xa70
 task_work_run+0x1d9/0x270
 do_exit+0x69b/0x2310
 do_group_exit+0x21b/0x2d0
 get_signal+0x1284/0x1330
 arch_do_signal_or_restart+0xbc/0x830
 exit_to_user_mode_loop+0x86/0x480
 do_syscall_64+0x2b7/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88810568bf80: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 ffff88810568c000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88810568c080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                  ^
 ffff88810568c100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88810568c180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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