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

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Message-ID: <SJ0P101MB03687BF7D5A10FD3C49C51E5F42E2@SJ0P101MB0368.NAMP101.PROD.OUTLOOK.COM>
Date: Mon, 25 Nov 2024 12:16:09 +0000
From: "Dalmas, Marcelo (GE Vernova)" <marcelo.dalmas@...com>
To: "jstultz@...gle.com" <jstultz@...gle.com>,
        "tglx@...utronix.de"
	<tglx@...utronix.de>,
        "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: [PATCH] ntp: fix bug in adjtimex reading time offset

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).

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;
        }

        result = ntpdata->time_state;
--
2.39.5