linux-kernel - [PATCH] linux/kernel.h: fix overflow for DIV_ROUND_UP

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Date:   Tue, 25 Jun 2019 15:35:18 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] linux/kernel.h: fix overflow for DIV_ROUND_UP_ULL

DIV_ROUND_UP_ULL adds the two arguments and then invokes
DIV_ROUND_DOWN_ULL. But on a 32bit system the addition of two 32 bit
values can overflow. DIV_ROUND_DOWN_ULL does it correctly and stashes
the addition into a unsigned long long so cast the result to unsigned
long long here to avoid the overflow condition.

Signed-off-by: Vinod Koul <vkoul@...nel.org>
---
 include/linux/kernel.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 74b1ee9027f5..1214fb48cfc8 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -93,7 +93,8 @@
 #define DIV_ROUND_DOWN_ULL(ll, d) \
 	({ unsigned long long _tmp = (ll); do_div(_tmp, d); _tmp; })
 
-#define DIV_ROUND_UP_ULL(ll, d)		DIV_ROUND_DOWN_ULL((ll) + (d) - 1, (d))
+#define DIV_ROUND_UP_ULL(ll, d) \
+	({ DIV_ROUND_DOWN_ULL((unsigned long long)(ll) + (d) - 1, (d)) })
 
 #if BITS_PER_LONG == 32
 # define DIV_ROUND_UP_SECTOR_T(ll,d) DIV_ROUND_UP_ULL(ll, d)
-- 
2.20.1