timekeeping: Prevent 32bit truncation in scale64_check_overflow()

[ 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>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1ce7c404d0b03556f71bcef3c3acd0148c7d3ef8..5b6f815a74ee3aff720479a888e08730bc966a42 100644 (file)
--- 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;
 }