Hundreds of null PATH records for *init_module syscall audit logs

[Paul Moore]

On Fri, Mar 3, 2017 at 4:14 PM, Richard Guy Briggs <rgb at redhat.com> wrote:
> On 2017-02-28 23:15, Steve Grubb wrote:
>> On Tuesday, February 28, 2017 10:37:04 PM EST Richard Guy Briggs wrote:
>> > Sorry, I forgot to include Cc: in this cover letter for context to the 4
>> > alt patches.
>> >
>> > On 2017-02-28 22:15, Richard Guy Briggs wrote:
>> > > The background to this is:
>> > >   https://github.com/linux-audit/audit-kernel/issues/8
>> > >
>> > > In short, audit SYSCALL records for *init_module were occasionally
>> > > accompanied by hundreds to thousands of null PATH records.
>> > >
>> > > I chatted with Al Viro and Eric Paris about this Friday afternoon and
>> > > they seemed to vaguely recall this issue and didn't have any solid
>> > > recommendations as to what was the right thing to do (other than the
>> > > same suggestion from both that I won't print here).
>> > >
>> > > It was reproducible on a number of vintages of distributions with
>> > > default kernels, but triggering on very few of the many modules loaded
>> > > at boot time.  It was reproduced with fs-nfs4 and nfsv4 modules on
>> > > tracefs, but there are reports of it also happening with debugfs.  It
>> > > was triggering only in __audit_inode_child with a parent that was not
>> > > found in the task context's audit names_list.
>> > >
>> > > I have four potential solutions listed in my order of preference and I'd
>> > > like to get some feedback about which one would be the most acceptable.
>>
>> 0.5 - Notice that we are in *init_module & delete_module and inhibit
>> generation of any record type except SYSCALL and KERN_MODULE ? There are some
>> classification routines for -F perms=wrxa that might be used to create a new
>> class for loading/deleting modules that sets a flag that we use to suppress
>> some record types.
>
> Ok, I was partially able to do this.
>
> If I try and catch it in audit_log_start() which is the common point for
> all the record types to be able to limit to just SYSCALL and
> KERN_MODULE, there will already be a linked list of hundreds to
> thousands of audit_names and will still print a non-zero items count in
> the SYSCALL record.  This also sounds like a potentially lazy way to
> deal with other record spam (like setuid BRPM_FCAPS).
>
> If I catch it in __audit_inode_child in the same place as I caught the
> filesystem type, it is effective for only the PATH record, which is all
> that is a problem at the moment.
>
> It touches nine arch-related files, which is a lot more disruptive than
> I was hoping.

Blocking PATH record on creation based on syscall *really* seems like
a bad/dangerous idea.  If we want to block all these tracefs/debugfs
records, let's just block the fs.  Although as of right now I'm not a
fan of blocking anything.

-- 
paul moore
www.paul-moore.com