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

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Message-ID: <87wmgoy435.ffs@tglx>
Date: Wed, 27 Nov 2024 18:33:02 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: "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>
Cc: "Dalmas, Marcelo (GE Vernova)" <marcelo.dalmas@...com>
Subject: Re: [PATCH] ntp: fix bug in adjtimex reading time offset

On Wed, Nov 27 2024 at 15:10, Thomas Gleixner wrote:

> On Mon, Nov 25 2024 at 12:16, Marcelo Dalmas wrote:
>> Due to an unsigned cast, adjtimex returns wrong offest when using ADJ_MICRO and the offset is negative.
>> In this case a small negative offset return approximately 4.29 seconds (~ 2^32/1000 milliseconds).
>
> Nice find. Please format the changelog to be within ~72 characters per
> line next time.
>
>> Signed-off-by: Marcelo Dalmas <marcelo.dalmas@...com>
>> ---
>>  kernel/time/ntp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
>> index b550ebe0f03b..02e7fe6a0afa 100644
>> --- a/kernel/time/ntp.c
>> +++ b/kernel/time/ntp.c
>> @@ -798,7 +798,7 @@ int __do_adjtimex(struct __kernel_timex *txc, const struct timespec64 *ts,
>>
>>                 txc->offset = shift_right(ntpdata->time_offset * NTP_INTERVAL_FREQ, NTP_SCALE_SHIFT);
>>                 if (!(ntpdata->time_status & STA_NANO))
>> -                       txc->offset = (u32)txc->offset / NSEC_PER_USEC;
>> +                       txc->offset /= NSEC_PER_USEC;
>
> This patch is white space damaged. (tabs are replaced with spaces).
>
> I fixed it up to you this time. Please send your next patch to yourself
> first and verify that it applies cleanly.

And it triggers a compile fail on 32bit as txc::offset is of type 'long
long'.