linux-kernel - Re: [PATCH] ntp: fix bug in adjtimex reading time offset

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Message-ID: <87r06wy3sf.ffs@tglx>
Date: Wed, 27 Nov 2024 18:39:28 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Richard Cochran <richardcochran@...il.com>
Cc: "Dalmas, Marcelo (GE Vernova)" <marcelo.dalmas@...com>,
 "jstultz@...gle.com" <jstultz@...gle.com>, "sboyd@...nel.org"
 <sboyd@...nel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ntp: fix bug in adjtimex reading time offset

On Wed, Nov 27 2024 at 18:35, Thomas Gleixner wrote:
> On Wed, Nov 27 2024 at 08:05, Richard Cochran wrote:
>> On Wed, Nov 27, 2024 at 03:10:30PM +0100, Thomas Gleixner wrote:
>>     The patch was generated by the following coccinelle script:
>>
>>     ...
>>
>> So I guess combining random other manual fixes into a patch that
>> claims to be generated is a bad idea?
>
> Indeed. I just figured out why the cast is there. txc::time_offset is of
> type 'long long', so the division triggers a build fail on 32-bit.
>
> It want's to be:
>
>    txc->time_offset = div_s64(txc->time_offset, NSEC_PER_USEC);

Or simpler by using a (s32) cast instead, which is sufficient as
time_offset must be in the range of [INT_MIN ... INT_MAX] because
NTP_SCALE_SHIFT is 32.