[debbugs-tracker] bug#18857: closed (floating point exception on invalid argument)

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Your message dated Mon, 27 Oct 2014 22:24:48 -0700
with message-id <address@hidden>
and subject line Re: [bug-diffutils] bug#18857: floating point exception on 
invalid argument
has caused the debbugs.gnu.org bug report #18857,
regarding floating point exception on invalid argument
to be marked as done.

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18857: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18857
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> --- Begin Message ---
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> Subject: 
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> floating point exception on invalid argument
>
>
>
>
> Date: 
>
> Mon, 27 Oct 2014 21:06:01 +0100
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> User-agent: 
>
> Mutt/1.5.22 (2013-10-16)
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>
>
>
> Hi,
>
> on 64 bit systems, an invalid tabsize argument can trigger a floating
> point exception:
>
> $ diff --tabsize=9223372036854775808 . .
> Floating point exception
>
> Offending line is this one:
>     intmax_t off = (w + t + GUTTER_WIDTH_MINIMUM) / (2 * t)  *  t;
>
> The tabsize I supplied is 2^63, multiplying by 2 will be 2^64 which
> is too large, so the divisor overflows to 0.
>
> This is a purely cosmetical fix, I don't see the need to adjust anything
> except avoiding this special value.  I doubt that anyone ever needed
> these large numbers.
>
>
> Tobias
>
> --- diffutils-3.3/src/diff.c~   2014-10-27 20:54:30.968656876 +0100
> +++ diffutils-3.3/src/diff.c    2014-10-27 20:54:41.360708407 +0100
> @@ -594,7 +594,7 @@
>  
>         case TABSIZE_OPTION:
>           numval = strtoumax (optarg, &numend, 10);
> -         if (! (0 < numval && numval <= SIZE_MAX) || *numend)
> +         if (! (0 < numval && numval <= SIZE_MAX / 2) || *numend)
>             try_help ("invalid tabsize '%s'", optarg);
>           if (tabsize != numval)
>             {
>
>
>
> --- End Message ---

--- Begin Message --- Subject: Re: [bug-diffutils] bug#18857: floating point exception on invalid argument Date: Mon, 27 Oct 2014 22:24:48 -0700 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

Tobias Stoeckmann wrote:

I don't see the need to adjust anything
except avoiding this special value.  I doubt that anyone ever needed
these large numbers.

Yes, it's hard to imagine anyone needing a tabsize that large. Still, the GNU policy is to avoid unnecessary limits, so it's better to make the limit as large as easily possible, which here would be SIZE_MAX - GUTTER_WIDTH_MINIMUM. Also, I see there are other ways the nearby code can overflow. Plus, we should put in a test case for this bug. So I installed the attached patch, which should address these issues. Thanks for reporting the problem.

0001-diff-fix-integer-overflow-problem-with-tabsize.patch
Description: Text document

--- End Message ---