From 499485a67fbacf4d9afbdb43522388c64f853428 Mon Sep 17 00:00:00 2001 From: Ruslan Valiyev Date: Wed, 26 Aug 2026 10:46:54 +0200 Subject: [PATCH] serial: core: fix NULL pointer dereference in serial_core_unregister_port() port->port_dev is NULL when no port device is installed: it is cleared on teardown, and never set if registration failed before serial_core_port_device_add(). serial_core_unregister_port() passes it straight to serial_core_get_ctrl_dev(), which dereferences it: KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047] RIP: serial_core_unregister_port Call Trace: serial8250_unregister_port serial8250_remove unbind_store Return early when there is no port device, and read port->port_dev under port_mutex. Also clear port->port_dev on the serial_core_register_port() error path, where the port device has already been removed. Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM") Reported-by: syzbot+9f57c1b2792029198fcf@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9f57c1b2792029198fcf Cc: stable@kernel.org Assisted-by: Claude:claude-opus-5 Assisted-by: Codex:gpt-5.6-sol Signed-off-by: Ruslan Valiyev Link: https://syzkaller.appspot.com/bug?extid=9f57c1b2792029198fcf Link: https://lore.kernel.org/all/20260826073237.1377668-1-linuxoid@gmail.com/ Reviewed-by: Tony Lindgren Link: https://patch.msgid.link/20260826084654.1392851-1-linuxoid@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/serial_core.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 33c8f3b6ac81..6332ed545c89 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -3381,6 +3381,7 @@ int serial_core_register_port(struct uart_driver *drv, struct uart_port *port) err_unregister_port_dev: serial_base_port_device_remove(port->port_dev); + port->port_dev = NULL; err_unregister_ctrl_dev: serial_base_ctrl_device_remove(new_ctrl_dev); @@ -3395,12 +3396,24 @@ err_unregister_ctrl_dev: void serial_core_unregister_port(struct uart_driver *drv, struct uart_port *port) { struct device *phys_dev = port->dev; - struct serial_port_device *port_dev = port->port_dev; - struct serial_ctrl_device *ctrl_dev = serial_core_get_ctrl_dev(port_dev); + struct serial_port_device *port_dev; + struct serial_ctrl_device *ctrl_dev; int ctrl_id = port->ctrl_id; guard(mutex)(&port_mutex); + /* + * A NULL port device means there is no registered port device to + * remove: serial_core_remove_one_port() clears port_dev on + * teardown, and it is never set if registration failed before + * serial_core_port_device_add(). + */ + port_dev = port->port_dev; + if (!port_dev) + return; + + ctrl_dev = serial_core_get_ctrl_dev(port_dev); + port->flags |= UPF_DEAD; serial_core_remove_one_port(drv, port);