A completely reasonable LSM would be a discretionary time lock.
The owner could set or unset the times when a file might be accessed.
Stored as an xattr, but neither a label nor Mandatory Access Control.
I propose this as an example of why the name maclabel is inappropriate,
because in this case the data involved is neither. Please also consider
that, as horrible as it may seem, an LSM could legitimately require
more than one xattr. A proper Compartmented Mode Workstation, for
example, might have a MAC label and an Information label, and as anyone
familiar with the CMW spec will tell you, they have to be separate.
Granted, the information label is only supposed to be used to indicate
the actual sensitivity of information, but if it's available someone is
going to use it programaticly.
I'll grant you the xattr bit.
The paradigm is* a security "blob" which is meaningfull only to the
security module proper. This is what allows SELinux to use secids and
Smack to toss around text strings. It's not MAC data and it's not
an NFS label, it's private to the LSM. It makes a lot of sense to use
an xattr to store a blob but, as the AppArmor people have been known
espouse, it's not the only way. The blob could be referenced from a
table using the inode number (it has been done on other systems and
works fine) rather than an xattr, in which case the whole "name" may
be meaningless.
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* It was when the whole thing started out at least.
Casey Schaufler
casey@schaufler-ca.com
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