Re: Need some security advice for systemtap

[David Smith <dsmith@redhat.com>]

Frank Ch. Eigler wrote:
> David Smith <dsmith@redhat.com> writes:
> 
>> [...]
>> Solving both problems would look like this:
>>
>> (A) A sysadmin would compile systemtap tap scripts into kernel modules
>> and store the module in something like
>> /etc/systemtap/authorized_modules/$kernel_version/foo.ko
> 
> The suggestion of using /lib/modules itself is a great one.

I'm OK with that.  From later in your email it looks like you are 
shooting for /lib/modules/`uname -r`/systemtap, which seems reasonable.

  >> [...]
>> (D) staprun.auth will need to disallow certain staprun.auth
>> command-line arguments, such as:
>> - "-c CMD" [...]
>> - "-O FILE" [...]
> 
> Actually, it doesn't.  A setuid program can drop its privileges after
> performing the root-only operations (module loading), and invoke the
> rest of the normal commands as the real userid.

Hmm.


I was trying to duplicate as little of staprun as possible - just parse 
arguments, make sure the module is in the correct place, then exec 
staprun for all the real processing.  I was trying to make staprun_auth 
a very thin wrapper around staprun.

With your idea I don't see a way around duplicating all of staprun (not 
actual code duplication, but compiling all of staprun into staprun_auth).

Perhaps there is a merged approach.  Keep staprun_auth a thin wrapper 
around staprun, but change staprun to raise and lower privileges as 
needed when inserting/removing modules, setting up relayfs, etc.

-- 
David Smith
dsmith@redhat.com
Red Hat
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