uid<-->username question

[John Dennis]

LC Bruzenak wrote:
> All,
>
> I was thinking about a scheme to retrieve usernames from UIDs on
> different machines. I was going to push the passwd file from a
> participating audit client up to the server. Then I'll store it uniquely
> according to its IP address (e.g. /var/etc/passwd.192.168.10.10). 
>
> Then, I'd change the parse code which looks up the username from
> getpwuid().
>
> In the case where the host was localhost, I'd still use the getpwuid()
> call. In the case where it is another host, I'd use fgetpwent() on the
> particular host's passwd file.
> I see that the name-value cache will have to be modified or maybe a
> UID/hostname/username triplet cache will need to be used instead for
> UIDs.
>
> On the sender, I was thinking that I already have an excellent
> audit-based file watch in place. Ideally, on a /etc/passwd addition, I'd
> like to fire a rule to automatically send the modified hosts file up to
> the collector machine.
>
> Any thoughts on this? I realize in most systems an LDAP server is
> adequate for federated logins and no code changes or schemes are
> necessary. I do not have this and likely never will given my
> environment. I also have to ensure that the participating systems do not
> reuse old UIDs or remove expired ones from their password file.
>
> I also realize this code change may be of little use to the general
> community, but if I do this and others have similar restrictions I'd be
> happy to share what I do.
>
> Thx in advance,
> LCB.
>
>   
I think this approach is problematic. First of all the set of uid's from 
a given machine is ephemeral. The contents of the passwd file needs to 
be matched to a time interval matching the log data. Secondly, the 
passwd file is sensitive data, you probably do not want to be shipping 
that over the network and storing it without a lot of safeguards. 
Thirdly, it's not just uid's that are have local context (machine local 
and time local), gid's,  ip-addr -> hostname mapping, kernel version 
dependent data encodings, etc. are just some of the data you won't be 
able to interpret correctly at some point in the future on some 
disassociated remote machine.

Because there are many problems with taking the audit log in it's 
current form and storing it remotely for later analysis in IPA we are 
not going to collect the audit log in it's default form. Instead we're 
going to resolve (e.g. interpret using auparse terminology) all the data 
on the local machine *before* we collect and store it. We plan on doing 
this by writing a audispd plugin which resolves all the ambiguous local 
data as it's generated (and hence before it's ever collected). This 
solves both the locality of time and locality of host issues and 
tremendously simplifies post-mortum analysis because the log data will 
have been stripped of ambiguities and replaced with data that can simply 
be read and used with no extra processing.


-- 
John Dennis <jdennis at redhat.com>

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