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Date: Sun, 23 Oct 2016 22:23:06 -0700
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Subject: bug classification discussion
From: smalyshev@gmail.com (Stanislav Malyshev)

Hi!

We have had a bunch of bugs recently which are essentially one and the
same issue: PHP 5.6 allows only int-sized strings, but many functions
don't check the size of the string they produce. This can lead to int
overflows inside php and also can break other libraries that also assume
string sizes are ints and this can cause all kinds of weirdness.
However, these bugs are very unlikely to manifest in production setting
for one simple reason - they require PHP to run with no memory limit,
and I haven't seen many setups that run with no memory limit. I'm not
going to go into specifics here, since some of the issues are still not
fixed, but you can talk to me privately if you need examples or browse
changelogs of later 5.6 releases.

A twin brother of this is in 7.0 where there are just integer overflows
in string size calculations. Usually that requires huge strings as
inputs, so also requires running with no memory limit.

These bugs are now treated as security issues, due to the fact that in
theory somebody might be running with no memory limit and get huge
string as an input from user. However, it was questioned that we indeed
should treat them so, due to the fact that encountering them in
production is unlikely, and due to the fact that they require patching
in many places, and merging those fixes out-of-band creates significant
potential for bugs.

I'd like to hear feedback on this, especially - though definitely not
only! - from RMs and distro people.

There are some libraries (ICU, I'm looking at you!) which have much
lower limits and fixed buffers inside and unfortunately they don't
enforce or check those limits, they just kind of assume everybody is
nice. For those, I think we'd have to treat issues stemming from that as
security issues if they look exploitable. Also, some libraries have int
overflows independent of PHP (also needing huge strings to trigger) -
not sure what to do with those.

Would be glad to hear some discussion on this.
-- 
Stas Malyshev
smalyshev@gmail.com