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 <linuxoid@gmail.com>
Link: https://syzkaller.appspot.com/bug?extid=9f57c1b2792029198fcf
Link: https://lore.kernel.org/all/20260826073237.1377668-1-linuxoid@gmail.com/
Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
Link: https://patch.msgid.link/20260826084654.1392851-1-linuxoid@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions