[OpenAFS] Re: [OpenAFS-announce] OpenAFS Security Advisory 2007-001: privilege escalation in Unix-based clients

[Jeffrey Altman]

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Jason Edgecombe wrote:
> Dr A V Le Blanc wrote:
>> Hm, I have a difficulty about this one.  We have a large number of
>> systems
>> to which some thousands of users have access, virtually none of which
>> are authenticated in AFS.  These systems have almost their entire
>> /lib, /bin, and all of /usr in AFS.  A substantial part of them
>> would stop working if we had all suid/sgid programs disabled by
>> default.  Short of copying every single binary of this kind to the
>> local disk and chmoding it, I can't think how we can cope with
>> setting suid off.  Are we to have a permanent security hole?  Or is
>> there another way of dealing with this?
>>
>>      -- Owen
> If these are Linux systems, then you could try doing a loopback mount
> out of AFS. It's not as flexible, but would still work and would allow
> suid even when AFS disallows it.
> The basics are make a big file and format it as ext2/ext3/squashfs, put
> all of your binaries in it. Copy that file out to AFS and have clients
> mount that file as /usr, /lib, /bin.

The issue is that copying files out of /afs that have the suid bit set
is not safe as long as the cache contents were populated using an
unauthenticated connection to the file servers.  This is because when
unauthenticated connections are used there is no keying material
available to prevent modifications to either the status data that
indicates that a file should or should not be executed suid or the
contents of the file itself.

It is for this reason that suid is being disabled by default.  Of
course, if you want to execute processes out of /afs suid you can
do so simply by "fs setcell -cell <cellname> -suid".   You do not
need to use a loopback mount to work around the default settings of
the cache manager.

That being said, the only real workaround is to locally copy the
files using authenticated connections

  <obtain tokens>
  fs flush <dir>
  fs flush <file>
  cp -p <file> /local/path
  chmod xxx /local/path

and then execute the suid files from the local disk.

There simply is no other method available at the moment within AFS.

Jeffrey Altman
Secure Endpoints Inc.



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