[PATCH 1/2] serdev: ttyport: fix use-after-free on closed TTY

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>]

use-after-free is visible in serdev-ttyport, e.g. during system reboot
with Qualcomm Atheros Bluetooth.  The TTY is closed, thus "struct
tty_struct" is being released, but the hci_uart_qca driver performs
writes and flushes during system shutdown in qca_serdev_shutdown().

  Unable to handle kernel paging request at virtual address 0072662f67726fd7
  ...
  CPU: 6 PID: 1 Comm: systemd-shutdow Tainted: G        W          6.1.0-rt5-00325-g8a5f56bcfcca #8
  Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
  Call trace:
   tty_driver_flush_buffer+0x4/0x30
   serdev_device_write_flush+0x24/0x34
   qca_serdev_shutdown+0x80/0x130 [hci_uart]
   device_shutdown+0x15c/0x260
   kernel_restart+0x48/0xac

KASAN report:

  BUG: KASAN: use-after-free in tty_driver_flush_buffer+0x1c/0x50
  Read of size 8 at addr ffff16270c2e0018 by task systemd-shutdow/1

  CPU: 7 PID: 1 Comm: systemd-shutdow Not tainted 6.1.0-next-20221220-00014-gb85aaf97fb01-dirty #28
  Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
  Call trace:
   dump_backtrace.part.0+0xdc/0xf0
   show_stack+0x18/0x30
   dump_stack_lvl+0x68/0x84
   print_report+0x188/0x488
   kasan_report+0xa4/0xf0
   __asan_load8+0x80/0xac
   tty_driver_flush_buffer+0x1c/0x50
   ttyport_write_flush+0x34/0x44
   serdev_device_write_flush+0x48/0x60
   qca_serdev_shutdown+0x124/0x274
   device_shutdown+0x1e8/0x350
   kernel_restart+0x48/0xb0
   __do_sys_reboot+0x244/0x2d0
   __arm64_sys_reboot+0x54/0x70
   invoke_syscall+0x60/0x190
   el0_svc_common.constprop.0+0x7c/0x160
   do_el0_svc+0x44/0xf0
   el0_svc+0x2c/0x6c
   el0t_64_sync_handler+0xbc/0x140
   el0t_64_sync+0x190/0x194

Fixes: bed35c6dfa6a ("serdev: add a tty port controller driver")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 drivers/tty/serdev/serdev-ttyport.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
index d367803e2044..3d2bab91a988 100644
--- a/drivers/tty/serdev/serdev-ttyport.c
+++ b/drivers/tty/serdev/serdev-ttyport.c
@@ -91,6 +91,9 @@ static void ttyport_write_flush(struct serdev_controller *ctrl)
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return;
+
 	tty_driver_flush_buffer(tty);
 }
 
@@ -99,6 +102,9 @@ static int ttyport_write_room(struct serdev_controller *ctrl)
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return 0;
+
 	return tty_write_room(tty);
 }
 
@@ -172,6 +178,9 @@ static unsigned int ttyport_set_baudrate(struct serdev_controller *ctrl, unsigne
 	struct tty_struct *tty = serport->tty;
 	struct ktermios ktermios = tty->termios;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return -ENXIO;
+
 	ktermios.c_cflag &= ~CBAUD;
 	tty_termios_encode_baud_rate(&ktermios, speed, speed);
 
@@ -186,6 +195,9 @@ static void ttyport_set_flow_control(struct serdev_controller *ctrl, bool enable
 	struct tty_struct *tty = serport->tty;
 	struct ktermios ktermios = tty->termios;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return;
+
 	if (enable)
 		ktermios.c_cflag |= CRTSCTS;
 	else
@@ -201,6 +213,9 @@ static int ttyport_set_parity(struct serdev_controller *ctrl,
 	struct tty_struct *tty = serport->tty;
 	struct ktermios ktermios = tty->termios;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return -ENXIO;
+
 	ktermios.c_cflag &= ~(PARENB | PARODD | CMSPAR);
 	if (parity != SERDEV_PARITY_NONE) {
 		ktermios.c_cflag |= PARENB;
@@ -222,6 +237,9 @@ static void ttyport_wait_until_sent(struct serdev_controller *ctrl, long timeout
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return;
+
 	tty_wait_until_sent(tty, timeout);
 }
 
@@ -230,6 +248,9 @@ static int ttyport_get_tiocm(struct serdev_controller *ctrl)
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return -ENXIO;
+
 	if (!tty->ops->tiocmget)
 		return -ENOTSUPP;
 
@@ -241,6 +262,9 @@ static int ttyport_set_tiocm(struct serdev_controller *ctrl, unsigned int set, u
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
 	struct tty_struct *tty = serport->tty;
 
+	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
+		return -ENXIO;
+
 	if (!tty->ops->tiocmset)
 		return -ENOTSUPP;
 
-- 
2.34.1