Re: [PATCH] sysctl selinux: Don't look at table->de

[ebiederm@xmission.com (Eric W. Biederman)]

Stephen Smalley <sds@tycho.nsa.gov> writes:


>> > If the ctl_table supplied more information about the functional purpose
>> > and the security sensitivity of the sysctl, then we could leverage that
>> > information instead, as long as we can at least derive the current
>> > labelings from that information for compatibility.
>> 
>> What do information do you need to do need?  Do you need extra fields in
> sysctl?
>> I am more than willing to help but I am not familiar enough with selinux
>> to do a reasonable job on my own.
>
> At present, we map the sysctls into functional groups (e.g. net, vm,
> fs, ...) that parallel the sysctl hierarchy so that we can limit access
> to only those programs/processes that need access for their purpose, and
> further partition where it makes sense to do so.  We also separate out
> particularly security sensitive ones like modprobe and hotplug.  So if
> the ctl_table carried some indication of functional grouping and
> security relevance (for some relatively small number of equivalence
> classes), then we could map those to labels instead of the current
> scheme.  And if we could have the ctl_table inherit the information from
> its logical "parent" in the hierarchy by default, then it shouldn't
> require too invasive a patch.

Ok.  So basically what you need is a parent pointer or some other way
of getting the full sysctl_path.   All of the names that show up in /proc
are still present in the ctl_table.

Hmm.  In parse_table we actually call sysctl_perm at each path component,
I'm not doing that in proc_sysctl.c at the moment but that would be easy to
add.

I think I will look at adding the back pointers.  Adding the security
check during lookup is nice but it won't really give you the context
you could use.  There may be a point in adding a security check during
lookup as well, but I think the way the VFS works there are weird implications
there.

Eric