Re: Endless loop in version 1.6.26

On Fri, Dec 30, 2016 at 1:19 PM, John Bowler <
[email protected]> wrote:

> On Fri, Dec 30, 2016 at 6:07 AM, Glenn Randers-Pehrson <[email protected]>
>  wrote:
>
>> I was expecting this change to cause a regression of mozilla bug #1300661
>> but it doesn't. It seems that I neglected to back out the change from the
>> progressive reader, libpng16/pngpread.c lines 844-847:
>>
>
> This is the 'if' block that starts at line 673 in the git head (which is
> now 1.6.28beta01).
>

Yes.  I forgot to account for the APNG code that's been added to mozilla's
libpng.


>
> I think the png_warning which precedes this is saying the wrong thing; it
> says the compressed data is *truncated* but the test is for compressed data
> after the last image byte has been delivered.
>

The trouble is that zlib returns ZLIB_DATA_ERROR for various reasons, one
of which
is a missing or incorrect ADLER32.


>
> I'd recommend leaving it as it is with just the Mozilla fix to do
> png_benign_error/png_error
>

The problem with that is other ZLIB_DATA_ERROR that should be abandoned.
One
of those caused the "endless loop" mentioned in the title of this thread.

Glenn


> according to the png_set_option setting.  This does mean that the captcha
> will, I think, have garbage in the last row (libpng doesn't do the last
> png_push_process_row) but I assume that Mozilla have signed off on the fix
> as is.
>

Yes, Mozilla is currently using the ADLER32 fix.  But it doesn't all work
because it's not
built with zlib-1.2.8.1 or later.



>   Technically the whole image has garbage in it (i.e. libpng can't be sure
> it isn't corrupted from the first byte.)
>
>
Technically yes, but in this instance the CAPTCHA that gets displayed is
correct.

Glenn

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