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Fri, 23 Jul 2021 21:17:50 +0000 Subject: Re: [PATCH v6 08/13] iio: afe: rescale: reduce risk of integer overflow To: Liam Beguin , jic23@kernel.org, lars@metafoo.de, pmeerw@pmeerw.net Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, robh+dt@kernel.org References: <20210721030613.3105327-1-liambeguin@gmail.com> <20210721030613.3105327-9-liambeguin@gmail.com> From: Peter Rosin Organization: Axentia Technologies AB Message-ID: <9e0e4398-873e-b5c0-0f0c-50a186ed2228@axentia.se> Date: Fri, 23 Jul 2021 23:17:47 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: <20210721030613.3105327-9-liambeguin@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: sv-SE Content-Transfer-Encoding: 7bit X-ClientProxiedBy: HE1PR0701CA0067.eurprd07.prod.outlook.com (2603:10a6:3:64::11) To DB8PR02MB5482.eurprd02.prod.outlook.com (2603:10a6:10:eb::29) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.13.3] (85.229.94.233) by HE1PR0701CA0067.eurprd07.prod.outlook.com (2603:10a6:3:64::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4373.7 via Frontend Transport; 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> + s64 tmp, tmp2; > + u32 factor; > > switch (scale_type) { > case IIO_VAL_FRACTIONAL: > - *val *= rescale->numerator; > - *val2 *= rescale->denominator; > + if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) || > + check_mul_overflow(*val2, rescale->denominator, (s32 *)&tmp2)) { > + tmp = (s64)*val * rescale->numerator; > + tmp2 = (s64)*val2 * rescale->denominator; > + factor = gcd(tmp, tmp2); Hi! Reiterating that gcd() only works for unsigned operands, so this is broken for negative values. Cheers, Peter > + tmp = div_s64(tmp, factor); > + tmp2 = div_s64(tmp2, factor); > + } > + *val = tmp; > + *val2 = tmp2; > return scale_type; > case IIO_VAL_INT: > *val *= rescale->numerator; >