------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: syz-executor/8821 Modules linked in: CPU: 0 UID: 0 PID: 8821 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: 94 68 fd 0a 67 48 0f b9 3a eb 4a e8 68 a0 32 fd 48 8d 3d 91 68 fd 0a 67 48 0f b9 3a eb 37 e8 55 a0 32 fd 48 8d 3d 8e 68 fd 0a <67> 48 0f b9 3a eb 24 e8 42 a0 32 fd 48 8d 3d 8b 68 fd 0a 67 48 0f RSP: 0018:ffffc9000bb47578 EFLAGS: 00010293 RAX: ffffffff848f11fb RBX: 0000000000000003 RCX: ffff88803c4e1e80 RDX: 0000000000000000 RSI: ffffffff8e68e140 RDI: ffffffff8f8c7a90 RBP: 0000000000000000 R08: ffff88803c4e1e80 R09: 0000000000000005 R10: 0000000000000004 R11: 0000000000000000 R12: ffff88803431d000 R13: ffff88807774a860 R14: ffff88807774a878 R15: dffffc0000000000 FS: 0000000000000000(0000) GS:ffff888125e35000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000110c3b084e CR3: 0000000054794000 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+0x6c5/0x2310 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+0x87/0x4f0 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+0x2d0/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fdb8a78e15c Code: Unable to access opcode bytes at 0x7fdb8a78e132. RSP: 002b:00007ffc146418f0 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: fffffffffffffe00 RBX: 0000000000000003 RCX: 00007fdb8a78e15c RDX: 0000000000000030 RSI: 00007ffc146419b0 RDI: 00000000000000f9 RBP: 00007ffc1464195c R08: 0000000000000000 R09: 0079746972756365 R10: 00007ffc146412b0 R11: 0000000000000246 R12: 0000000000000258 R13: 00000000000927c0 R14: 000000000014aead R15: 00007ffc146419b0 ---------------- Code disassembly (best guess): 0: 94 xchg %eax,%esp 1: 68 fd 0a 67 48 push $0x48670afd 6: 0f b9 3a ud1 (%rdx),%edi 9: eb 4a jmp 0x55 b: e8 68 a0 32 fd call 0xfd32a078 10: 48 8d 3d 91 68 fd 0a lea 0xafd6891(%rip),%rdi # 0xafd68a8 17: 67 48 0f b9 3a ud1 (%edx),%rdi 1c: eb 37 jmp 0x55 1e: e8 55 a0 32 fd call 0xfd32a078 23: 48 8d 3d 8e 68 fd 0a lea 0xafd688e(%rip),%rdi # 0xafd68b8 * 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction 2f: eb 24 jmp 0x55 31: e8 42 a0 32 fd call 0xfd32a078 36: 48 8d 3d 8b 68 fd 0a lea 0xafd688b(%rip),%rdi # 0xafd68c8 3d: 67 addr32 3e: 48 rex.W 3f: 0f .byte 0xf