[PATCH v3] staging: greybus: uart: Fix atomicity violation in get_serial_info()

[PATCH v3] staging: 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.
V3:
Used the correct patch prefix.
Thanks Johan Hovold, Dan Carpenter, Alex Elder and Greg KH 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 v3] staging: greybus: uart: Fix atomicity violation in get_serial_info()

[Greg KH]

On Thu, Nov 07, 2024 at 07:33:37PM +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.

Trailing whitespace :(

You should fix your editor to highlight this so it doesn't keep showing
up.

> 
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")

My bot says:

----------

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
from other developers.

thanks,

greg k-h's patch email bot

Re: [PATCH v3] staging: greybus: uart: Fix atomicity violation in get_serial_info()

[Johan Hovold]

On Thu, Nov 07, 2024 at 04:11:00PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Nov 07, 2024 at 07:33:37PM +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.
> 
> Trailing whitespace :(
> 
> You should fix your editor to highlight this so it doesn't keep showing
> up.
> 
> > 
> > Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> > Fixes: 0aad5ad563c8 ("greybus/uart: switch to ->[sg]et_serial()")

> - 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.

The CC-stable tag was left out on purpose (on my request IIRC) as this
is not fixing anything that's really a problem and is basically just
shutting the static checker up.

I believe this was also reflected in the commit message of v2 (even if
"inconsistent" may have been a better word than "meaningless").

Johan

Re: [PATCH v3] staging: greybus: uart: Fix atomicity violation in get_serial_info()

[Dan Carpenter]

On Thu, Nov 07, 2024 at 04:11:00PM +0100, Greg KH wrote:
> 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
> from other developers.

Like Johan said, this doesn't really belong in stable because it doesn't affect
users.  It's mostly about correctness and static analysis.

The linux-media CI system has also started complaining if we don't add a stable
tag and it suggests that the correct thing is to add:

Cc: <stable+noautosel@kernel.org> # reason goes here, and must be present

Do we really have to do that?  Applying it to stable doesn't cause a problem,
it's just not necessary.

regards,
dan carpenter