On Mon, Sep 30, 2024 at 06:14:03PM +0800, Qiu-ji Chen wrote:
> Atomicity violation occurs during consecutive reads of the members of
> gb_tty. Consider a scenario where, because the consecutive reads of gb_tty
> members are not protected by a lock, the value of gb_tty may still be
> changing during the read process.
>
> gb_tty->port.close_delay and gb_tty->port.closing_wait are updated
> together, such as in the set_serial_info() function. If during the
> read process, gb_tty->port.close_delay and gb_tty->port.closing_wait
> are still being updated, it is possible that gb_tty->port.close_delay
> is updated while gb_tty->port.closing_wait is not. In this case,
> the code first reads gb_tty->port.close_delay and then
> gb_tty->port.closing_wait. A new gb_tty->port.close_delay and an
> old gb_tty->port.closing_wait could be read. Such values, whether
> before or after the update, should not coexist as they represent an
> intermediate state.
>
> This could result in a mismatch of the values read for gb_tty->minor,
No, gb_tty minor is only set at probe().
> gb_tty->port.close_delay, and gb_tty->port.closing_wait, which in turn
> could cause ss->close_delay and ss->closing_wait to be mismatched.
Sure, but that's a pretty minor issue as Dan already pointed out.
> To address this issue, we have enclosed all sequential read operations of
> the gb_tty variable within a lock. This ensures that the value of gb_tty
> remains unchanged throughout the process, guaranteeing its validity.
>
> This possible bug is found by an experimental static analysis tool
> developed by our team. This tool analyzes the locking APIs
> to extract function pairs that can be concurrently executed, and then
> analyzes the instructions in the paired functions to identify possible
> concurrency bugs including data races and atomicity violations.
>
> Fixes: b71e571adaa5 ("staging: greybus: uart: fix TIOCSSERIAL jiffies conversions")
And this obviously isn't the correct commit to blame. Please be more
careful.
> Cc: stable@xxxxxxxxxxxxxxx
Since this is unlikely to cause any issues for a user, I don't think
stable backport is warranted either.
> Signed-off-by: Qiu-ji Chen <chenqiuji666@xxxxxxxxx>
> ---
> 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 cdf4ebb93b10..8cc18590d97b 100644
> --- a/drivers/staging/greybus/uart.c
> +++ b/drivers/staging/greybus/uart.c
> @@ -595,12 +595,14 @@ 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;
gb_tty is not protected by the port mutex.
> 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;
> }
Johan
