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From: Yiyuan guo <yguoaz@gmail.com>
To: linux-kernel@vger.kernel.org
Cc: andy@kernel.org, tpiepho@gmail.com, akpm@linux-foundation.org,
	oskar@scara.com, Yiyuan guo <yguoaz@gmail.com>
Subject: A divide by zero bug in lib/math/rational.c (with triggering input)
Date: Fri, 21 May 2021 13:09:13 +0800	[thread overview]
Message-ID: <CAM7=BFoktwgy=T0GK6Mpmp2gYToCUs=CrM29MRWw8O7TPypQ8w@mail.gmail.com> (raw)

In the file lib/math/rational.c, the function
rational_best_approximation has the following
code:

void rational_best_approximation(
    unsigned long given_numerator, unsigned long given_denominator,
    unsigned long max_numerator, unsigned long max_denominator,
    unsigned long *best_numerator, unsigned long *best_denominator) {
   ...
   if ((n2 > max_numerator) || (d2 > max_denominator)) {
            unsigned long t = min((max_numerator - n0) / n1,
                          (max_denominator - d0) / d1);
   ...
}

d1 may be equal to zero when performing the division, leading to a
divide by zero problem.

One input  to trigger the divide by zero bug is:
rational_best_approximation(31415, 100, (1 << 8) - 1, (1 << 5) - 1, &n, &d)

             reply	other threads:[~2021-05-21  5:09 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-21  5:09 Yiyuan guo [this message]
     [not found] ` <CAHp75Vf8kQ73w0R9ieDNjDVkxM-V83QRN9mc6BjRZA8xHpPNAA@mail.gmail.com>
     [not found]   ` <CAHp75Vft8pnA+m0C=Ok7nRyjERAd2uJJ4q6HcN460j0Hir6Kaw@mail.gmail.com>
2021-05-21  7:55     ` A divide by zero bug in lib/math/rational.c (with triggering input) Yiyuan guo
2021-05-21  9:20       ` Trent Piepho
2021-05-21  9:53         ` Andy Shevchenko
2021-05-22 19:07           ` Oskar Schirmer
2021-05-24  3:20             ` Trent Piepho
2021-05-23  0:05           ` Trent Piepho

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