Re: [RFC] refining systemd mountpoints

Dominick Grift <[email protected]> Mon, 13 Jan 2020 11:18:25 +0100
Newsgroups	org.kernel.vger.selinux-refpolicy
Message-ID	<[email protected]>
On Mon, Jan 13, 2020 at 10:42:10AM +0100, Dominick Grift wrote:
> On Thu, Jan 09, 2020 at 10:42:40PM +0100, Dominick Grift wrote:
> > On Thu, Jan 09, 2020 at 04:06:38PM -0500, Chris PeBenito wrote:
> > > I'd like to refine how the policy handles systemd's mounton so that it works
> > > similar to how we manage mountpoints for mount_t. Since systemd can be made
> > > to mount over just about anything, I'm looking at adding a new conditional
> > > that would allow init_t to mounton non_security_file_type, and then an
> > > interface like files_mountpoint().
> > > 
> > > The question is for the implementation of the interface; I see two options,
> > > either the interface allows mounton for all file-like classes, or the
> > > classes are specified as a parameter:
> > > 
> > > --------
> > > init.te:
> > > attribute init_mountpoint_type;
> > > allow init_t init_mountpoint_type:dir_file_class_set mounton;
> > > 
> > > init.if:
> > > interface(`init_mountpoint',`
> > > typeattribute $1 init_mountpoint_type;
> > > ')

To be clear: I like this option:

1. You can BindPath/BindReadOnlyPath/BindReadWritePath/InaccessiblePath *any* file in theory. So dir_file_class_set seems appropriate.
2. You might wat to extend it just a little though:

allow init_t init_mountpoint_type:dir_file_class_set { getattr mounton };
allow init_t init_mountpoint_type:dir search_dir_perms;


> > > --------
> > > 
> > > or
> > > 
> > > --------
> > > init.if:
> > > interface(`init_mountpoint',`
> > > allow init_t $1:$2 mounton;
> > > ')
> > > --------
> > > 
> > > I like the first option because it is clearer since you can see the mounton
> > > in init.te, but that is excessive access.  The second option could be made
> > > to look like the first option, but it would need several attributes and
> > > interfaces, e.g. init_dir_mountpoint_type, init_file_mountpoint_type, etc.
> > > which isn't so desirable.
> > > 
> > > Any thoughts on this?
> > 
> > I implemented the former in my policy. ie the dir_file_class_set equiv..
> > 
> > 4163               (allow subj bind_path_obj_type_attribute (dirs (create)))
> > 4164               (allow subj bind_path_obj_type_attribute list_dir_perms)
> > 4165               (allow subj bind_path_obj_type_attribute (dir (mounton)))
> > 4166               (allow subj bind_path_obj_type_attribute create_file_perms)
> > 4167               (allow subj bind_path_obj_type_attribute (file (mounton)))
> > 
> > As you can see i even allow systemd to create the mountpoint in case it does not exist. For example if /etc/machine-id does not exist and I have a BindReadOnlyPath=/etc/machine-id then systemd will touch /etc/machine-id and mount it ro
> 
> 
> Okay, I think I am wrong. It will not create the bind_path if it does not exist. Not sure how I got to this...
> 
> > 
> > It also generally buggy. Systemd does not (alway's) use setfscreatecon to create the mountpoints. And sometimes it does use setfscreatecon where it shouldnt.
> > 
> > https://github.com/systemd/systemd/issues/13762
> > 
> > > 
> > > -- 
> > > Chris PeBenito
> > 
> > -- 
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> > Dominick Grift
> 
> 
> 
> -- 
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> Dominick Grift



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