Description:
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Original bug report: https://bugs.launchpad.net/ubuntu/+source/php7.0/+bug/1668017

Roughly, we produced a security/update update of the PHP7.0 package in Ubuntu which bumped up to 7.0.15. A user reported that this regressed their installation, specifically:

a web application serving rather big binary blobs from a MariaDB table. After the unattended update (7.0.8-0ubuntu0.16.04.3 to 7.0.15-0ubuntu0.16.04.2), the application would routinely break while trying to fetch a >16Mbyte row from the database server.

Requests resulting in a row under 16Mbyte are processed normally, anything above it would return columns in the wrong order, and right around 0xFFFFF2 a null-character (0x00) is inserted into the stream (when the resulting file is compared to one served with the version used previously)

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The prior (working) version was 7.0.8 based.

Test script:
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The reporter provided a relatively straightforward test case:

- Ubuntu 16.04
- MariaDB Server (not tested on mysql, but I expect similar results)
- php 7.0 (7.0.15)
- phpMyAdmin

Configuration:
MariaDB: max_allowed_packet = 128M
php: post_max_size and upload_max_filesize raised to 128M

Import the some SQL data, for instance: https://we.tl/vb37KISpUU.
This will build you a MyISAM table with 4 columns, 3x varchar(1) and 1 longblob. The table will have one big blob in it, with 32Mbyte worth of 0x20 (space)

Downloading the binary through phpMyAdmin on 7.0.15 will produce a file with a null-character inserted at (for my setup) 0xFFFFF6, the rest of the file is as expected.