greybus-dev June 2023

greybus-dev@lists.linaro.org

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[PATCH] staging: greybus: fix a possible data-inconsistency due to data race in get_serial_info()

by Tuo Li

The variables gb_tty->port.close_delay and gb_tty->port.closing_wait are ofter accessed together while holding the lock gb_tty->port.mutex. Here is an example in set_serial_info(): mutex_lock(&gb_tty->port.mutex); ... gb_tty->port.close_delay = close_delay; gb_tty->port.closing_wait = closing_wait; ... mutex_unlock(&gb_tty->port.mutex); However, they are accessed without holding the lock gb_tty->port.mutex when are accessed in get_serial_info(): ss->close_delay = jiffies_to_msecs(gb_tty->port.close_delay) / 10; ss->closing_wait = gb_tty->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ? ASYNC_CLOSING_WAIT_NONE : jiffies_to_msecs(gb_tty->port.closing_wait) / 10; In my opinion, this may be a harmful race, because ss->close_delay can be inconsistent with ss->closing_wait if gb_tty->port.close_delay and gb_tty->port.closing_wait are updated by another thread after the assignment to ss->close_delay. Besides, the select operator may return wrong value if gb_tty->port.closing_wait is updated right after the condition is calculated. To fix this possible data-inconsistency caused by data race, a lock and unlock pair is added when accessing different fields of gb_tty->port. Reported-by: BassCheck <bass(a)buaa.edu.cn> Signed-off-by: Tuo Li <islituo(a)gmail.com> --- drivers/staging/greybus/uart.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c index 20a34599859f..b8875517ea6a 100644 --- a/drivers/staging/greybus/uart.c +++ b/drivers/staging/greybus/uart.c @@ -596,12 +596,14 @@ static int get_serial_info(struct tty_struct *tty, { struct gb_tty *gb_tty = tty->driver_data; + mutex_lock(&gb_tty->port.mutex); ss->line = gb_tty->minor; ss->close_delay = jiffies_to_msecs(gb_tty->port.close_delay) / 10; ss->closing_wait = gb_tty->port.closing_wait == ASYNC_CLOSING_WAIT_NONE ? ASYNC_CLOSING_WAIT_NONE : jiffies_to_msecs(gb_tty->port.closing_wait) / 10; + mutex_unlock(&gb_tty->port.mutex); return 0; } -- 2.34.1

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greybus-dev June 2023