This is a note to let you know that I've just added the patch titled
serial: core: Clearing the circular buffer before NULLifying it
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-core-clearing-the-circular-buffer-before-nullifying-it.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 9cf7ea2eeb745213dc2a04103e426b960e807940 Mon Sep 17 00:00:00 2001
From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Date: Thu, 4 Apr 2024 17:59:26 +0300
Subject: serial: core: Clearing the circular buffer before NULLifying it
From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
commit 9cf7ea2eeb745213dc2a04103e426b960e807940 upstream.
The circular buffer is NULLified in uart_tty_port_shutdown()
under the spin lock. However, the PM or other timer based callbacks
may still trigger after this event without knowning that buffer pointer
is not valid. Since the serial code is a bit inconsistent in checking
the buffer state (some rely on the head-tail positions, some on the
buffer pointer), it's better to have both aligned, i.e. buffer pointer
to be NULL and head-tail possitions to be the same, meaning it's empty.
This will prevent asynchronous calls to dereference NULL pointer as
reported recently in 8250 case:
BUG: kernel NULL pointer dereference, address: 00000cf5
Workqueue: pm pm_runtime_work
EIP: serial8250_tx_chars (drivers/tty/serial/8250/8250_port.c:1809)
...
? serial8250_tx_chars (drivers/tty/serial/8250/8250_port.c:1809)
__start_tx (drivers/tty/serial/8250/8250_port.c:1551)
serial8250_start_tx (drivers/tty/serial/8250/8250_port.c:1654)
serial_port_runtime_suspend (include/linux/serial_core.h:667 drivers/tty/serial/serial_port.c:63)
__rpm_callback (drivers/base/power/runtime.c:393)
? serial_port_remove (drivers/tty/serial/serial_port.c:50)
rpm_suspend (drivers/base/power/runtime.c:447)
The proposed change will prevent ->start_tx() to be called during
suspend on shut down port.
Fixes: 43066e32227e ("serial: port: Don't suspend if the port is still busy")
Cc: stable <stable@xxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202404031607.2e92eebe-lkp@xxxxxxxxx
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240404150034.41648-1-andriy.shevchenko@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 1 +
1 file changed, 1 insertion(+)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1788,6 +1788,7 @@ static void uart_tty_port_shutdown(struc
* Free the transmit buffer.
*/
uart_port_lock_irq(uport);
+ uart_circ_clear(&state->xmit);
buf = state->xmit.buf;
state->xmit.buf = NULL;
uart_port_unlock_irq(uport);
Patches currently in stable-queue which might be from andriy.shevchenko@xxxxxxxxxxxxxxx are
queue-6.8/serial-8250_dw-revert-do-not-reclock-if-already-at-correct-rate.patch
queue-6.8/serial-core-clearing-the-circular-buffer-before-nullifying-it.patch
queue-6.8/gpiolib-swnode-remove-wrong-header-inclusion.patch
