linux-kernel - [PATCH v3 1/8] rtl2832: use 64-bit arithmetic instead of 32-bit in rtl2832_set

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Date:   Tue, 6 Feb 2018 10:46:59 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Antti Palosaari <crope@....fi>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Subject: [PATCH v3 1/8] rtl2832: use 64-bit arithmetic instead of 32-bit in
 rtl2832_set_frontend

Add suffix ULL to constant 7 in order to give the compiler complete
information about the proper arithmetic to use. Notice that this
constant is used in a context that expects an expression of type
u64 (64 bits, unsigned).

The expression dev->pdata->clk * 7 is currently being evaluated
using 32-bit arithmetic.

Addresses-Coverity-ID: 1271223 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
Changes in v2:
 - Update subject and changelog to better reflect the proposed code changes.
 - Add suffix ULL to constant instead of casting a variable.

Changes in v3:
 - Mention the specific Coverity report in the commit message.

 drivers/media/dvb-frontends/rtl2832.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/dvb-frontends/rtl2832.c b/drivers/media/dvb-frontends/rtl2832.c
index 94bf5b7..fa3b816 100644
--- a/drivers/media/dvb-frontends/rtl2832.c
+++ b/drivers/media/dvb-frontends/rtl2832.c
@@ -498,7 +498,7 @@ static int rtl2832_set_frontend(struct dvb_frontend *fe)
 	* RSAMP_RATIO = floor(CrystalFreqHz * 7 * pow(2, 22)
 	*	/ ConstWithBandwidthMode)
 	*/
-	num = dev->pdata->clk * 7;
+	num = dev->pdata->clk * 7ULL;
 	num *= 0x400000;
 	num = div_u64(num, bw_mode);
 	resamp_ratio =  num & 0x3ffffff;
@@ -511,7 +511,7 @@ static int rtl2832_set_frontend(struct dvb_frontend *fe)
 	*	/ (CrystalFreqHz * 7))
 	*/
 	num = bw_mode << 20;
-	num2 = dev->pdata->clk * 7;
+	num2 = dev->pdata->clk * 7ULL;
 	num = div_u64(num, num2);
 	num = -num;
 	cfreq_off_ratio = num & 0xfffff;
-- 
2.7.4