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Bug #75139 php-7.1.9/ext/gd/libgd/gd_interpolation.c:1786: suspicious if ?
Submitted: 2017-08-31 07:20 UTC Modified: 2017-09-01 21:47 UTC
From: dcb314 at hotmail dot com Assigned: cmb
Status: Closed Package: GD related
PHP Version: 7.1.9RC1 OS: linux
Private report: No CVE-ID:
 [2017-08-31 07:20 UTC] dcb314 at hotmail dot com
Description:
------------
[php-7.1.9/ext/gd/libgd/gd_interpolation.c:1786]: (style) Same expression on both sides of '&&'.

Source code is

    const gdFixed f_slop = f_slop_x > 0 && f_slop_x > 0 ?
                            f_slop_x > f_slop_y ? gd_divfx(f_slop_y, f_slop_x) : gd_divfx(f_slop_x, f_slop_y)
                        : 0;

BTW, using nested ternary operators is asking for trouble.
Suggest recode in a simpler way.



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 [2017-08-31 14:00 UTC] cmb@php.net
-Assigned To: +Assigned To: cmb
 [2017-08-31 22:10 UTC] cmb@php.net
-Package: Compile Warning +Package: GD related
 [2017-08-31 22:10 UTC] cmb@php.net
It seems to me that is actually a bug, because
`f_slop_x > 0 && f_slop_x > 0` appears to be supposed to be
`f_slop_x > 0 && f_slop_y > 0` to avoid a subsequent division by
zero.

Thanks for reporting this issue!

A test exhibiting the current misbehavior would be welcome.
 [2017-09-01 21:47 UTC] cmb@php.net
-Status: Assigned +Status: Analyzed
 [2017-09-01 21:47 UTC] cmb@php.net
This very issue has been fixed in external libgd with
<https://github.com/libgd/libgd/commit/dd48286>. However, it seems
to me that a division by zero cannot occur, because `f_slop_y` can
only be zero if `_angle` is 0 or π, but in the former case
`f_slop_x` would be 1, and the latter case cannot happen due to
the switch in gdImageRotateInterpolated().

Anyhow, the respective code has been removed with
<https://github.com/libgd/libgd/commit/2b26be8> to improve the
quality of the rotation result.

Neither of these, nor other, patches regarding gd_interpolation.c
has made it to our bundled libgd yet, unfortunately. I am
uncertain whether 2b26be8 could be backported without some other
patches, so I think it is best to fix the typo for PHP 7.0+, and
to try to sync the whole file for PHP 7.3+.

> BTW, using nested ternary operators is asking for trouble.
> Suggest recode in a simpler way.

As the code is likely to vanish, putting the inner ternary
operation in parentheses appears to be sufficient.
 [2017-09-01 22:29 UTC] cmb@php.net
Automatic comment on behalf of cmbecker69@gmx.de
Revision: http://git.php.net/?p=php-src.git;a=commit;h=e20a6b0213e108da50293d1fff885f507e6115ac
Log: Fixed bug #75139 (libgd/gd_interpolation.c:1786: suspicious if ?)
 [2017-09-01 22:29 UTC] cmb@php.net
-Status: Analyzed +Status: Closed
 
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