[apparmor] security_path hooks for xattr

[Miklos Szeredi]

Forwarding from an internal bug report:

   "AppArmor does not mediate the xattr system calls for confined processes.

   As a consequence, a confined process can cross the confinement privilege
   boundary by reading or writing to extended attributes that the confined
   task should not have access to. The restrictions for security and user
   attributes read and write still apply according to DAC; however, this
   does not comply with the claim of AppArmor to mediate fipe
   operations. The use of extended attributes is very flexible, so that the
   effect of a missing mediation can lead to false assumptions in
   subsequent policy decisions (eCryptfs)."

AFAIU this boils down to missing security hooks in *xattr().

Would it be possible to add these hooks?

Thanks,
Miklos