linux-audit: reconstruct path names from syscall events?

[Eric Paris]

Casey only talked about the easy part of the reason the pathnames are
useless.  He forgot to mention that the linux kernel has mount
namespaces.  There is absolutely no reason why one could not mount a FS
in the init namespace, launch a whole 'virtual machine' in that new FS,
and then unmount the FS from the initial namespace.  Now we have 2
COMPLETELY disjoint 'filesystems'.

The audit logs, and things like /proc/pid/fd or dpath functions are all
going to be relative to the local FS namespace.  Sometimes it just quite
simply can't be resolved.  So now inside virtual machine namespace they
might read/modify /etc/shadow and that file IS /etc/shadow.  There is no
other 'path' for that file.  True its not the same /etc/shadow as the
one in the init fs namespace.  And at some point there may have existed
a path in the init namespace /mnt/virt1/etc/shadow which also
represented that inode, but at this point in time the ONLY path which
represents this file is /etc/shadow.

Audit logs based on name are wrong and misleading.  There's a reason the
auditable object is the inode and fs details Casey mentioned.  We might
be able to usually give me information, but that information cannot EVER
be used for anything useful.  Its unreliable.  Exposing it only leads
one to believe they have knowledge they don't.

-Eric