[PATCH ghak95] audit: Do not log full CWD path on empty relative paths

[Paul Moore]

On Tue, Nov 13, 2018 at 10:25 AM Ondrej Mosnacek <omosnace at redhat.com> wrote:
> On Tue, Nov 6, 2018 at 9:19 PM Paul Moore <paul at paul-moore.com> wrote:
> > On Tue, Nov 6, 2018 at 3:09 AM Ondrej Mosnacek <omosnace at redhat.com> wrote:
> > > On Tue, Nov 6, 2018 at 12:30 AM Paul Moore <paul at paul-moore.com> wrote:
> > > > Let's reset this discussion a bit ... if we abolish relative paths and
> > > > make everything absolute, is there even a need to log PARENT?
> > >
> > > If there ever was such need, then this won't change when we switch to
> > > absolute paths. The PATH records contain some fields (inode, dev, obj,
> > > ...) that can be different for the child and parent and I would say
> > > these are the only new information that the PARENT records provide
> > > over the corresponding CREATE/DELETE records.
> >
> > Sigh.  Of course the inode information is going to be different
> > between the object in question and the parent, they are different
> > filesystem objects.  Ask your self the bigger question: does the
> > PARENT record provide me any security relevant information related to
> > the filesystem object that is being accessed?
>
> I would say it does. Consider e.g. the "mode" and "obj" fields. When
> you move (rename) a file from one directory to another (which is the
> main, if not the only, case when a PARENT record is emitted), then you
> are usually more interested in the values for the parent directory
> than the file itself (that's what determines if you can move the
> file).

I disagree on the importance of the mode/obj of the parent in a rename
operation.  From my perspective I really only care about the
filesystem object that is being moved and if it succeeded or not.  The
idea that you care more about the parent than the object being moved
makes no sense to me at all.

> For example, assume you have a rule that logs whenever some sensitive
> file gets moved. You do not expect that to happen because you set the
> file/directory permissions and labels so that it can't be done by
> anyone unauthorized. But something goes wrong, the permissions/labels
> get changed somehow ...

In which case you should be watching for changes to the filesystem
metadata which affect access rights.  That is how you should catch
changes to permissions on a filesystem object as it gives you
information about the change as well as the subject information of the
user/process which made the change.

> ... and a bad actor leverages the situation to move
> the file. Then later you want to investigate this security incident
> and as part of it you want to know what permissions were set on the
> directories involved that had allowed the file to be moved, because
> this may give you a useful lead. With PARENT records, you get such
> information, without them you don't.

If you only have that information in the parent record then you are
missing half the story, and it may be the important half as the
interesting bit of information in this example is the identity of the
user/process which was able to change permissions to enable the rename
to take place.

Unless Steve provides evidence of some compelling certification
requirement which necessitates the need for a parent record, I see no
reason to keep it.

-- 
paul moore
www.paul-moore.com