[PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Qiu-ji Chen]

Our static checker found a bug where set_serial_info() uses a mutex, but 
get_serial_info() does not. Fortunately, the impact of this is relatively 
minor. It doesn't cause a crash or any other serious issues. However, if a 
race condition occurs between set_serial_info() and get_serial_info(), 
there is a chance that the data returned by get_serial_info() will be 
meaningless.

Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")
---
V2:
Modified the patch description to make it more concise and easier to understand.
Changed the fix code to ensure the logic is correct.
Thanks to Johan Hovold and Dan Carpenter for helpful suggestion.
---
 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..8eab94cb06fa 100644
--- a/drivers/staging/greybus/uart.c
+++ b/drivers/staging/greybus/uart.c
@@ -596,11 +596,13 @@ static int get_serial_info(struct tty_struct *tty,
 	struct gb_tty *gb_tty = tty->driver_data;
 
 	ss->line = gb_tty->minor;
+	mutex_lock(&gb_tty->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;
 }
-- 
2.34.1

Re: [PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Dan Carpenter]

On Wed, Nov 06, 2024 at 05:58:19PM +0800, Qiu-ji Chen wrote:
> Our static checker found a bug where set_serial_info() uses a mutex, but 
> get_serial_info() does not. Fortunately, the impact of this is relatively 
> minor. It doesn't cause a crash or any other serious issues. However, if a 
> race condition occurs between set_serial_info() and get_serial_info(), 
> there is a chance that the data returned by get_serial_info() will be 
> meaningless.
> 
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")
> ---

Thanks!

Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>

regards,
dan carpenter

Re: [PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Alex Elder]

On 11/6/24 3:58 AM, Qiu-ji Chen wrote:
> Our static checker found a bug where set_serial_info() uses a mutex, but
> get_serial_info() does not. Fortunately, the impact of this is relatively
> minor. It doesn't cause a crash or any other serious issues. However, if a
> race condition occurs between set_serial_info() and get_serial_info(),
> there is a chance that the data returned by get_serial_info() will be
> meaningless.
> 
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")

Looks good.

Reviewed-by: Alex Elder <elder@riscstar.com>

PS  I was going to suggest computing the close delay and closing wait
     outside the mutex, as get_serial_info() above it does.  But it's
     minor and there's no reason to hold up your patch for that.

> ---
> V2:
> Modified the patch description to make it more concise and easier to understand.
> Changed the fix code to ensure the logic is correct.
> Thanks to Johan Hovold and Dan Carpenter for helpful suggestion.
> ---
>   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..8eab94cb06fa 100644
> --- a/drivers/staging/greybus/uart.c
> +++ b/drivers/staging/greybus/uart.c
> @@ -596,11 +596,13 @@ static int get_serial_info(struct tty_struct *tty,
>   	struct gb_tty *gb_tty = tty->driver_data;
>   
>   	ss->line = gb_tty->minor;
> +	mutex_lock(&gb_tty->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;
>   }

Re: [PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Johan Hovold]

On Wed, Nov 06, 2024 at 05:58:19PM +0800, Qiu-ji Chen wrote:
> Our static checker found a bug where set_serial_info() uses a mutex, but 
> get_serial_info() does not. Fortunately, the impact of this is relatively 
> minor. It doesn't cause a crash or any other serious issues. However, if a 
> race condition occurs between set_serial_info() and get_serial_info(), 
> there is a chance that the data returned by get_serial_info() will be 
> meaningless.
> 
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")
> ---
> V2:
> Modified the patch description to make it more concise and easier to understand.
> Changed the fix code to ensure the logic is correct.
> Thanks to Johan Hovold and Dan Carpenter for helpful suggestion.

Much better, thanks.

But please try to use the same patch prefix as previous patches for the
driver you're modifying (e.g. by looking at git log --oneline for the
driver in question).

In this case it should have been:

	staging: greybus: uart: fix ...

so that it's clear where this patch should be applied.

Care to fix that up in a v3?

Reviewed-by: Johan Hovold <johan+linaro@kernel.org>

Johan

Re: [PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Greg KH]

On Wed, Nov 06, 2024 at 05:58:19PM +0800, Qiu-ji Chen wrote:
> Our static checker found a bug where set_serial_info() uses a mutex, but 
> get_serial_info() does not. Fortunately, the impact of this is relatively 
> minor. It doesn't cause a crash or any other serious issues. However, if a 
> race condition occurs between set_serial_info() and get_serial_info(), 
> there is a chance that the data returned by get_serial_info() will be 
> meaningless.
> 
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")
> ---
> V2:
> Modified the patch description to make it more concise and easier to understand.
> Changed the fix code to ensure the logic is correct.
> Thanks to Johan Hovold and Dan Carpenter for helpful suggestion.
> ---
>  drivers/staging/greybus/uart.c | 2 ++
>  1 file changed, 2 insertions(+)

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
  signed-off-by area at all, which means that the patch will not be
  applied to any older kernel releases.  To properly fix this, please
  follow the documented rules in the
  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
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thanks,

greg k-h's patch email bot

Re: [PATCH v2] greybus/uart: Fix atomicity violation in get_serial_info()

[Greg KH]

On Wed, Nov 06, 2024 at 05:58:19PM +0800, Qiu-ji Chen wrote:
> Our static checker found a bug where set_serial_info() uses a mutex, but 
> get_serial_info() does not. Fortunately, the impact of this is relatively 
> minor. It doesn't cause a crash or any other serious issues. However, if a 
> race condition occurs between set_serial_info() and get_serial_info(), 
> there is a chance that the data returned by get_serial_info() will be 
> meaningless.

You have trailing whitespace in your changelog text for some reason :(