From: Ivan Pravdin ipravdin.official@gmail.com
[ Upstream commit ca94b2b036c22556c3a66f1b80f490882deef7a6 ]
Currently, bcsp_recv() can be called even when the BCSP protocol has not been registered. This leads to a NULL pointer dereference, as shown in the following stack trace:
KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f] RIP: 0010:bcsp_recv+0x13d/0x1740 drivers/bluetooth/hci_bcsp.c:590 Call Trace: <TASK> hci_uart_tty_receive+0x194/0x220 drivers/bluetooth/hci_ldisc.c:627 tiocsti+0x23c/0x2c0 drivers/tty/tty_io.c:2290 tty_ioctl+0x626/0xde0 drivers/tty/tty_io.c:2706 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
To prevent this, ensure that the HCI_UART_REGISTERED flag is set before processing received data. If the protocol is not registered, return -EUNATCH.
Reported-by: syzbot+4ed6852d4da4606c93da@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=4ed6852d4da4606c93da Tested-by: syzbot+4ed6852d4da4606c93da@syzkaller.appspotmail.com Signed-off-by: Ivan Pravdin ipravdin.official@gmail.com Signed-off-by: Luiz Augusto von Dentz luiz.von.dentz@intel.com Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
YES – Guarding `bcsp_recv()` until the HCI UART core has successfully registered the driver prevents the real NULL-deref crash syzbot found, and the change is tiny, self-contained, and consistent with the rest of the UART transports.
- `bcsp_complete_rx_pkt()` still hands completed frames to the core with `hci_recv_frame(hu->hdev, …)` (`drivers/bluetooth/hci_bcsp.c:562`), so if registration fails or has not finished, `hu->hdev` stays NULL and the dereference blows up exactly as in the reported stack trace. - The fix adds a single early `test_bit(HCI_UART_REGISTERED…)` gate (`drivers/bluetooth/hci_bcsp.c:585-586`). Returning `-EUNATCH` in this situation matches what the other UART transports already do (`drivers/bluetooth/hci_h4.c:112-113`, `drivers/bluetooth/hci_bcm.c:698-699`, etc.), so runtime behavior becomes consistent across protocols. - Callers ignore the return value and only bump stats when `hu->hdev` is valid (`drivers/bluetooth/hci_ldisc.c:618-631`), so refusing to process data before registration has no side effects beyond dropping input that could not be delivered anyway. - `HCI_UART_REGISTERED` is set only after `hci_register_dev()` succeeds (`drivers/bluetooth/hci_ldisc.c:691-699`) and is left clear when the registration path fails and `hu->hdev` is nulled (`drivers/bluetooth/hci_ldisc.c:693-695`), so the new guard precisely covers the hazardous window. - The change is minimal (two new lines), purely defensive, and fixes a syzbot-reported NULL dereference without touching protocol state machines or timing, making it an excellent candidate for stable backporting.
drivers/bluetooth/hci_bcsp.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/drivers/bluetooth/hci_bcsp.c b/drivers/bluetooth/hci_bcsp.c index 664d82d1e6139..591abe6d63ddb 100644 --- a/drivers/bluetooth/hci_bcsp.c +++ b/drivers/bluetooth/hci_bcsp.c @@ -582,6 +582,9 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count) struct bcsp_struct *bcsp = hu->priv; const unsigned char *ptr;
+ if (!test_bit(HCI_UART_REGISTERED, &hu->flags)) + return -EUNATCH; + BT_DBG("hu %p count %d rx_state %d rx_count %ld", hu, count, bcsp->rx_state, bcsp->rx_count);