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That helper checks HCI_FORCE_BREDR_SMP, updates hdev->smp_bredr_data, and then toggles the force flag. Two same-value writers can both pass the state check and run the same enable or disable transition on one hdev. On the disable side, one writer can clear hdev->smp_bredr_data while the other still observes the old force flag and later passes NULL into smp_del_chan(). The double transition can also leave the force flag out of sync with the requested state. Take hci_dev_lock() around smp_force_bredr() in the debugfs write path so each request observes and applies one stable BR/EDR SMP transition. Validation reproduced this kernel report: KASAN null-ptr-deref in smp_del_chan+0x31/0x90 RIP: 0033:0x7faae680d340 RIP: 0010:smp_del_chan+0x31/0x90 [bluetooth] Read of size 8 Call Trace: dump_stack_lvl+0x66/0xa0 kasan_report+0xe0/0x110 smp_del_chan+0x31/0x90 smp_force_bredr+0x69/0xc0 trace_clock_x86_tsc+0x20/0x20 srso_alias_return_thunk+0x5/0xfbef5 lock_acquire+0xd0/0x300 ksys_write+0xd2/0x170 full_proxy_write+0x9e/0xd0 vfs_write+0x1b0/0x810 find_held_lock+0x2b/0x80 do_user_addr_fault+0x65a/0x890 rcu_is_watching+0x20/0x50 do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f Fixes: 300acfdec916 ("Bluetooth: Introduce force_bredr_smp debugfs option for testing") Assisted-by: Codex:gpt-5.5 Signed-off-by: Cen Zhang --- v2: - Reword commit message to avoid checkpatch's 75-character line warning. net/bluetooth/hci_debugfs.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c index b7f682922a16..ff344564c923 100644 --- a/net/bluetooth/hci_debugfs.c +++ b/net/bluetooth/hci_debugfs.c @@ -520,7 +520,9 @@ static ssize_t force_bredr_smp_write(struct file *file, if (err) return err; + hci_dev_lock(hdev); err = smp_force_bredr(hdev, enable); + hci_dev_unlock(hdev); if (err) return err; -- 2.43.0