[PATCH 5.15.y] serial: core: shut down initialized port on removal

[Sasha Levin <sashal@kernel.org>]

From: Igor Putko <igorpetindev@gmail.com>

[ Upstream commit 810d467c11f0c85107874d08dfdd11acba6aa0c0 ]

When a serial port configured as a console is opened and subsequently
closed, tty_port_shutdown() skips invoking port->ops->shutdown() because
port->console is true. As a result, tty_port_initialized() remains true
and the port's interrupt handler stays registered in the irq subsystem.

If the underlying device is later unbound or removed (e.g. via sysfs
driver unbind or device hot-unplug), serial_core_remove_one_port()
unregisters the console, frees uport->name via kfree(), and tears down
the port without shutting it down or freeing its IRQ. Consequently, the
irqaction descriptor remains registered in genirq with action->name
pointing to freed memory.

This triggers a use-after-free read whenever genirq accesses action->name,
such as when reading /proc/interrupts:

  BUG: KASAN: slab-use-after-free in string+0x476/0x570
  Call Trace:
   string+0x476/0x570
   vsnprintf+0x422/0x1300
   seq_printf+0x...
   show_interrupts+...

Fix this by acquiring port->mutex in serial_core_remove_one_port() after
console unregistration, clearing port->console under the mutex to prevent
data races with concurrent tty_port_shutdown(), and invoking
uart_shutdown(NULL, state) if the port remains initialized. This ensures
that port->ops->shutdown() is called and the IRQ is freed before
kfree(uport->name).

Reported-by: syzbot+843bf2f48f4d12e6682e@syzkaller.appspotmail.com
Cc: stable <stable@kernel.org>
Closes: https://syzkaller.appspot.com/bug?extid=843bf2f48f4d12e6682e
Fixes: 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close")
Fixes: f7048b15900f ("tty: serial_core: Add name field to uart_port struct")
Signed-off-by: Igor Putko <igorpetindev@gmail.com>
Link: https://patch.msgid.link/20261003163337.45577-1-igorpetindev@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ sashal: Replaced scoped_guard() with explicit mutex_lock() and mutex_unlock() for GNU89 compatibility. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/serial_core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a52e88a750f9e..3fc3b33cadc51 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3071,6 +3071,13 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
 	if (uart_console(uport))
 		unregister_console(uport->cons);
 
+	mutex_lock(&port->mutex);
+	port->console = false;
+
+	if (tty_port_initialized(port))
+		uart_shutdown(NULL, state);
+	mutex_unlock(&port->mutex);
+
 	/*
 	 * Free the port IO and memory resources, if any.
 	 */
-- 
2.53.0