Description:
------------
An image, seen in the wild and probably generated non-maliciously,
reliably causes exif_read_data() to go into infinite recursion.

I've fixed the problem and created a patch against PHP 4.4.0:

http://wikimedia.org/~tstarling/php/exif_IFD2.patch

The test image is here:

http://wikimedia.org/~tstarling/php/Carcraftbuckett.jpg

The problem was an assumption that images would follow the spec and
include a maximum of 2 IFD headers, IFD0 for the image and IFD1 for the
thumbnail. The test image probably has the "next IFD offset" field
pointing back to the same structure, creating an infinite loop. I
haven't studied the test image in detail, but my patch allows PHP's Exif
functions to read it without segfaulting, which is good enough for me.

I decided to ignore any further IFDs beyond the first two rather than
issue an error, for compatibility with possible future revisions of the
Exif spec.

-- Tim Starling (MediaWiki developer)

Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

There are no significant changes between 4.4.0 and HEAD, you should be
able to forward-port it without any trouble. See

http://cvs.php.net/diff.php/php-src/ext/exif/exif.c?r1=1.173&r2=1.118.2.
37.2.1&ty=h

My patch comes in at around line 3039, as you can see there are only
documentation changes.

This patch is now in production on wikipedia.org and related websites. I
for one don't want to see my website get DoSed because of this.

Assigned to the "maintainer".

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

Fixed for 4.4.1, 5.0.6, 5.1.0, HEAD