linux-kernel - [PATCH 4.4 017/230] atm: he: fix sign-extension overflow on large shift

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Message-Id: <20190322111237.966968897@linuxfoundation.org>
Date:   Fri, 22 Mar 2019 12:12:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Colin Ian King <colin.king@...onical.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 017/230] atm: he: fix sign-extension overflow on large shift

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit cb12d72b27a6f41325ae23a11033cf5fedfa1b97 ]

Shifting the 1 by exp by an int can lead to sign-extension overlow when
exp is 31 since 1 is an signed int and sign-extending this result to an
unsigned long long will set the upper 32 bits.  Fix this by shifting an
unsigned long.

Detected by cppcheck:
(warning) Shifting signed 32-bit value by 31 bits is undefined behaviour

Signed-off-by: Colin Ian King <colin.king@...onical.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/atm/he.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/atm/he.c b/drivers/atm/he.c
index 0f5cb37636bcc..010581e8bee05 100644
--- a/drivers/atm/he.c
+++ b/drivers/atm/he.c
@@ -717,7 +717,7 @@ static int he_init_cs_block_rcm(struct he_dev *he_dev)
 			instead of '/ 512', use '>> 9' to prevent a call
 			to divdu3 on x86 platforms
 		*/
-		rate_cps = (unsigned long long) (1 << exp) * (man + 512) >> 9;
+		rate_cps = (unsigned long long) (1UL << exp) * (man + 512) >> 9;
 
 		if (rate_cps < 10)
 			rate_cps = 10;	/* 2.2.1 minimum payload rate is 10 cps */
-- 
2.19.1