Hi,
We run a shared hosting company as well and taken upon the route to
patch the linux kernel to allow switching of user of the current
process. An apache module allows you to switch the process based on the
virtual host. Our current module also implements mass virtual hosting,
but any open source module should also work with normal vhost files.
We've been discussing this in the PHP internals mailing list and are
preparing an open source solution, which can be tested by interested
parties. Please read the message below, where security concerns of the
PHP are addressed. I'll be sure to post a message on the apache list
when the patch is made ready for public viewing.
Best regards,
Arnold Daniels
Javeline (www.javeline.net)
-------------------------
Rik Arends schreef:
Hi Andi,
I'm Rik Arends, i co-wrote the kernel patch + apache module for
in-process user switching.
After reading your concerns i might shed some light on these issues.
First of all, i know that there are some possible security holes with
this system.
One of the biggest problems i could see is triggering a bufferoverflow
in mod_php, so the user can get its own assembler code to run.
Then by knowing how to do the kernel calls, he could, theoretically
switch the user of the process back to www-data, after which he could
switch to
any 'shared hosting user' (not just any user) in the system to access
their shared hosting files.
The complexity of this hack, plus that your apaches will be
segfaulting continously while a person is trying this might not make
it too plausible to happen.
Second, the main system would not be at risk, just some of the shared
hosting users-files that might be accessed. In 99.99% of the cases,
there really is not all that much to steal and the amount of effort to
actually hack this is pretty huge and requires exploitation of a
hardcore hole in an in-process scripting engine (mod_php for
instance), plus the knowledge on how to trigger the right kernel
calls, and the userID's to switch to (which, unless the user somehow
gained shell access to his targets directory he has no clue about)
The same way i think we can approach the, the 'resources that are
still open from other users' hole, if it might be there. I expect
mod_php or other modules to do proper cleanup of their handles or else
they would be leaking a lot in an apache process thats being reused.
This is not a new problem, and also a very very difficult one to
succesfully exploit.
Say we have 256 apache processes with user switching. You are
targetting site X running on the 'same machine'. Then you'd have to
poll continously and hope you are served by an apache process that
also served the other site AND know which resources to access, and how
to do that. Please note that you can only use the resource leak bug
when you are using an in-process scripting engine so you cant just go
poke around your memory. This same 'bug' if you will is also there in
shared hosting structures with reused apache processes that don't do
user switching at all. Again the risk of this exploit actually being
used seems well, remote. Add to this the fact that in shared hosting
environments, nobody runs any security critical applications such as
full creditcard payment systems. For that people employ their own
server with SSL and certificates. That is just beyond the scale of
shared hosting.
I hope i might have lessened your concerns. I think the security risk
our patch poses is mostly theoretical, have a very difficult exploit
route and in almost all cases have a 0 to almost nil payoff. Its much
much simpler to try to hack the other persons site via bugs in forms
or other installed applications.
Regards,
Rik Arends
-------- Originele bericht --------
Onderwerp: RE: [PHP-DEV] Comments on PHP security
Datum: Thu, 18 Jan 2007 14:14:17 -0800
Van: Andi Gutmans <[EMAIL PROTECTED]>
Aan: 'Arnold Daniels' <[EMAIL PROTECTED]>, <[email protected]>
I haven't seen the patch yet but my concern would be with resources
which have already been opened. Unless you guys clean that up in
between requests it can be very dangerous as I doubt Linux
re-verify's permissions when those are accessed. In any case, I'd be
happy to review and might be completely wrong...
-------------------------
Nick Kew schreef:
On Mon, 29 Jan 2007 20:31:40 -0600
<[EMAIL PROTECTED]> wrote:
I have gotten the impression this may be a sore subject for the list
based on searching through the archives, but I do not intend to work
anyone up. I have been trying to find a solution to the problem of
shared hosting with a dynamic language such as PHP. I found the old
perchild MPM and it appears it is not being maintained or there was
possibly a design problem. I would like to know two things.
1. Is there a mechanism (other than suexec) that allows functionality
similar to perchild, that will allow a uid to be assigned on a per
request basis?
There are several third-party solutions: google for metux, peruser,
mod_ruid, and fastcgi.
2. If there is, do the developers need help with it? I can write C
and I am willing to help out with this. If there is not, Would
anyone from the Apache team be interested in working with me so I may
write such functionality, maybe for a future version of Apache?
Patches welcome.
Bear in mind that perchild was threaded, and therefore never
likely to be suitable for php.
