------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#1: syz-executor/17648 Modules linked in: CPU: 1 UID: 0 PID: 17648 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28 Code: d4 91 fe 0a 67 48 0f b9 3a eb 4a e8 c8 0c 33 fd 48 8d 3d d1 91 fe 0a 67 48 0f b9 3a eb 37 e8 b5 0c 33 fd 48 8d 3d ce 91 fe 0a <67> 48 0f b9 3a eb 24 e8 a2 0c 33 fd 48 8d 3d cb 91 fe 0a 67 48 0f RSP: 0018:ffffc900030575b8 EFLAGS: 00010293 RAX: ffffffff848deb0b RBX: 0000000000000003 RCX: ffff88802a9e3d00 RDX: 0000000000000000 RSI: ffffffff8e68e200 RDI: ffffffff8f8c7ce0 RBP: 0000000000000000 R08: ffff88802a9e3d00 R09: 0000000000000005 R10: 0000000000000004 R11: 0000000000000000 R12: ffff88806a78a000 R13: ffff888059678060 R14: ffff888059678078 R15: dffffc0000000000 FS: 0000000000000000(0000) GS:ffff888125f1f000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000abd030 CR3: 000000000dd3a000 CR4: 00000000003526f0 Call Trace: __refcount_sub_and_test include/linux/refcount.h:400 [inline] __refcount_dec_and_test include/linux/refcount.h:432 [inline] refcount_dec_and_test include/linux/refcount.h:450 [inline] kref_put include/linux/kref.h:64 [inline] klist_dec_and_del+0x3c7/0x3d0 lib/klist.c:206 klist_put lib/klist.c:217 [inline] klist_del lib/klist.c:230 [inline] klist_remove+0x1bd/0x340 lib/klist.c:249 device_move+0x193/0x730 drivers/base/core.c:4615 hci_conn_del_sysfs+0xb8/0x1a0 net/bluetooth/hci_sysfs.c:75 hci_conn_cleanup net/bluetooth/hci_conn.c:173 [inline] hci_conn_del+0xc36/0x1240 net/bluetooth/hci_conn.c:1234 hci_conn_hash_flush+0x191/0x260 net/bluetooth/hci_conn.c:2638 hci_dev_close_sync+0x821/0x1100 net/bluetooth/hci_sync.c:5326 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline] hci_unregister_dev+0x21a/0x5b0 net/bluetooth/hci_core.c:2715 vhci_release+0x152/0x1a0 drivers/bluetooth/hci_vhci.c:690 __fput+0x44c/0xa70 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:233 exit_task_work include/linux/task_work.h:40 [inline] do_exit+0x694/0x22f0 kernel/exit.c:971 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112 get_signal+0x1285/0x1340 kernel/signal.c:3034 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline] exit_to_user_mode_loop+0x87/0x4e0 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x2b7/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fcfaefc2005 Code: Unable to access opcode bytes at 0x7fcfaefc1fdb. RSP: 002b:00007ffc6f6ce250 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6 RAX: 0000000000000000 RBX: 000000000000041f RCX: 00007fcfaefc2005 RDX: 00007ffc6f6ce290 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007ffc6f6ce2fc R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000001388 R13: 00000000000927c0 R14: 00000000000ae52b R15: 00007ffc6f6ce350 ---------------- Code disassembly (best guess), 1 bytes skipped: 0: 91 xchg %eax,%ecx 1: fe 0a decb (%rdx) 3: 67 48 0f b9 3a ud1 (%edx),%rdi 8: eb 4a jmp 0x54 a: e8 c8 0c 33 fd call 0xfd330cd7 f: 48 8d 3d d1 91 fe 0a lea 0xafe91d1(%rip),%rdi # 0xafe91e7 16: 67 48 0f b9 3a ud1 (%edx),%rdi 1b: eb 37 jmp 0x54 1d: e8 b5 0c 33 fd call 0xfd330cd7 22: 48 8d 3d ce 91 fe 0a lea 0xafe91ce(%rip),%rdi # 0xafe91f7 * 29: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2e: eb 24 jmp 0x54 30: e8 a2 0c 33 fd call 0xfd330cd7 35: 48 8d 3d cb 91 fe 0a lea 0xafe91cb(%rip),%rdi # 0xafe9207 3c: 67 addr32 3d: 48 rex.W 3e: 0f .byte 0xf