linux-kernel - Re: [PATCH] time: copy tai value (International Atomic Time, in seconds) to output __user struct in get_old

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Date:   Thu, 01 Dec 2022 16:18:26 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jake Macneal <jake.macneal@...il.com>
Cc:     linux-kernel@...r.kernel.org, John Stultz <jstultz@...gle.com>,
        Stephen Boyd <sboyd@...nel.org>, arnd@...db.de
Subject: Re: [PATCH] time: copy tai value (International Atomic Time, in
 seconds) to output __user struct in get_old_timex32().

Jake,

On Thu, Dec 01 2022 at 10:00, Jake Macneal wrote:
>>> This is despite all other fields of the corresponding __kernel_timex
>>> struct being copied to the old_timex32 __user struct in this function.
>
>> This is completely backwards. get_old_timex32() copies from the user
>> supplied old_timex32 struct to the __kernel_timex struct, no?
>
> You're totally right, I managed to mix up the order right off the bat.
>
>> I'm not against this change per se, but the justification for it really
>> boils down to:
>
>>     Make it consistent with the regular syscall
>

> I agree, that's a better summary. There isn't any effect in the kernel
> now due to get_old_timex32() ignoring the tai value from userspace. So
> this patch would be purely aesthetic, although one might argue that
> copying the userspace tai value into txc is also less likely to lead
> to a bug in the future, were any of the functions do_adjtimex(),
> __do_adjtimex(), or process_adjtimex_modes() to be changed in a way so
> that the userspace tai value became used (I realize this is unlikely).

Right. Unlikely or not, consistency is always a good thing.

> I apologize for any confusion I caused.

No problem. Been there, done that :)

Thanks,

        tglx