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