From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754862AbeBOTZF (ORCPT ); Thu, 15 Feb 2018 14:25:05 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:38889 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750832AbeBOTZD (ORCPT ); Thu, 15 Feb 2018 14:25:03 -0500 Subject: NACK: [PATCH] rtc: tx4939: avoid unintended sign extension on a 24 bit shift From: Colin Ian King To: Alessandro Zummo , Alexandre Belloni , linux-rtc@vger.kernel.org Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180215185941.27547-1-colin.king@canonical.com> Message-ID: <39b61428-be04-7233-edd8-ab7b37b469d0@canonical.com> Date: Thu, 15 Feb 2018 19:25:01 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180215185941.27547-1-colin.king@canonical.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/02/18 18:59, Colin King wrote: > From: Colin Ian King > > The shifting of buf[5] by 24 bits to the left will be promoted to > a 32 bit signed int and then sign-extended to an unsigned long. If > the top bit of buf[5] is set then all then all the upper bits sec > end up as also being set because of the sign-extension. Fix this by > casting buf[5] to an unsigned long before the shift. > > Detected by CoverityScan, CID#1465292 ("Unintended sign extension") > > Fixes: 0e1492330cd2 ("rtc: add rtc-tx4939 driver") > Signed-off-by: Colin Ian King > --- > drivers/rtc/rtc-tx4939.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/rtc/rtc-tx4939.c b/drivers/rtc/rtc-tx4939.c > index feededce3ded..b8a066cbcc42 100644 > --- a/drivers/rtc/rtc-tx4939.c > +++ b/drivers/rtc/rtc-tx4939.c > @@ -170,7 +170,8 @@ static int tx4939_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm) > alrm->enabled = (ctl & TX4939_RTCCTL_ALME) ? 1 : 0; > alrm->pending = (ctl & TX4939_RTCCTL_ALMD) ? 1 : 0; > spin_unlock_irq(&pdata->lock); > - sec = (buf[5] << 24) | (buf[4] << 16) | (buf[3] << 8) | buf[2]; > + sec = ((unsigned long)buf[5] << 24) | (buf[4] << 16) | > + (buf[3] << 8) | buf[2]; > rtc_time_to_tm(sec, &alrm->time); > return rtc_valid_tm(&alrm->time); > } > Nack, there are two occurrences of this sign extension, I missed the other one. I'll re-send a fix. Colin