[PATCH v4 2/5] serial: core: clear freed pointers on uart_register_driver() failure

uart_register_driver() leaves drv->state pointing to freed memory when
tty_alloc_driver() fails. If tty_register_driver() fails, drv->tty_driver
also retains a pointer after its reference is dropped.

Drivers that use drv->state as an "already registered" flag can then skip
registration on the next probe and pass the freed state to
uart_add_one_port().

This issue was found with failslab on QEMU's raspi1ap board by
failing registration and binding the PL011 port again.

Clear both pointers on their failure paths, as uart_unregister_driver()
already does.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: 9e845abfc8a8 ("serial: fix NULL pointer dereference")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <[email protected]>
---
 drivers/tty/serial/serial_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 03ee3d038f4e..234976fb2a87 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2777,8 +2777,10 @@ int uart_register_driver(struct uart_driver *drv)
 	for (i = 0; i < drv->nr; i++)
 		tty_port_destroy(&drv->state[i].port);
 	tty_driver_kref_put(normal);
+	drv->tty_driver = NULL;
 out_kfree:
 	kfree(drv->state);
+	drv->state = NULL;
 out:
 	return retval;
 }
-- 
2.53.0