[PATCH AUTOSEL 4.14 057/127] timekeeping: Prevent 32bit truncation in scale64_check_overflow()

Sasha Levin
2020-09-18T02:34:41Z

From: Wen Yang <wenyang@linux.alibaba.com>

[ Upstream commit 4cbbc3a0eeed675449b1a4d080008927121f3da3 ]

While unlikely the divisor in scale64_check_overflow() could be >= 32bit in
scale64_check_overflow(). do_div() truncates the divisor to 32bit at least
on 32bit platforms.

Use div64_u64() instead to avoid the truncation to 32-bit.

[ tglx: Massaged changelog ]

Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200120100523.45656-1-wenyang@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/time/timekeeping.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1ce7c404d0b03..5b6f815a74ee3 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -988,9 +988,8 @@ static int scale64_check_overflow(u64 mult, u64 div, u64 *base)
((int)sizeof(u64)*8 - fls64(mult) < fls64(rem)))
return -EOVERFLOW;
tmp *= mult;
- rem *= mult;

- do_div(rem, div);
+ rem = div64_u64(rem * mult, div);
*base = tmp + rem;
return 0;
}
--
2.25.1