From: Paul Moore <paul@paul-moore.com>
To: James Carter <jwcart2@gmail.com>
Cc: Ondrej Mosnacek <omosnace@redhat.com>,
SElinux list <selinux@vger.kernel.org>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Vivek Goyal <vgoyal@redhat.com>, Daniel Walsh <dwalsh@redhat.com>,
Zdenek Pytela <zpytela@redhat.com>
Subject: Re: virtiofs and its optional xattr support vs. fs_use_xattr
Date: Wed, 9 Dec 2020 21:39:57 -0500 [thread overview]
Message-ID: <CAHC9VhQkSA5VteHfu8TyBp7wqDspoLCOP+sB7vaV4XCQ8vwBeA@mail.gmail.com> (raw)
In-Reply-To: <CAP+JOzQ-s9ASgqFt7HVyY1R7JKQ85Ee-=iou0C5xRRvaSZo52Q@mail.gmail.com>
On Wed, Dec 9, 2020 at 10:37 AM James Carter <jwcart2@gmail.com> wrote:
> On Tue, Dec 8, 2020 at 6:45 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Mon, Dec 7, 2020 at 12:17 PM James Carter <jwcart2@gmail.com> wrote:
> > > On Mon, Dec 7, 2020 at 9:45 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > > >
> > > > Hi everyone,
> > > >
> > > > In [1] we ran into a problem with the current handling of filesystem
> > > > labeling rules. Basically, it is only possible to specify either
> > > > genfscon or fs_use_xattr for a given filesystem, but in the case of
> > > > virtiofs, certain mounts may support security xattrs, while other ones
> > > > may not.
> > > >
> > > > So we can't use the xattr support by adding fs_use_xattr virtiofs
> > > > (...); to the policy, because then a non-xattr mount will fail
> > > > (SELinux does a mount-time check on the root inode to make sure that
> > > > the xattr handler works), but we also don't want to stay on genfscon,
> > > > because then we can't relabel files.
> > > >
> > > > So my question is how to best address this? One option is to use a
> > > > similar "hack" as for cgroupfs; i.e. do a kind of mixed genfs-xattr
> > > > labeling, but that's ugly and requires hard-coding another FS name in
> > > > the selinux code. The only other alternative I could come up with is
> > > > to add a new FS labeling statement that would specify some kind of
> > > > mixed genfscon / fs_use_xattr behavior. That would be a better
> > > > long-term solution, but leads to more questions on how such statement
> > > > should actually work... Should it work the cgroupfs way, giving a
> > > > default label to everything and allowing to set/change labels via
> > > > xattrs? Or should it rather just detect xattrs support and switch
> > > > between SECURITY_FS_USE_XATTR and SECURITY_FS_USE_GENFS behavior based
> > > > on that? In the latter case, should the statement specify two contexts
> > > > (one for fs_use_xattr and another one for genfscon) or just one for
> > > > both behaviors?
> > >
> > > I don't think adding a new statement is necessary. It seems like
> > > allowing both fs_use_xattr and genfscon rules for the filesystem in
> > > policy and then using the fs_use_xattr rule if xattrs are supported
> > > while falling back to the genfscon rule if they are not would do what
> > > you need.
> >
> > That seems reasonable to me so long as this ambiguity is okay with the
> > folks who do policy analysis. Thinking quickly I'm not sure why it
> > would be a problem, but the thought did occur while I was typing up
> > this reply ...
>
> I don't think that it would cause a problem with policy analysis. I
> think that you would just assume the genfscon rule is being used,
> since it is less fine-grained. It wouldn't be much different from how
> booleans are handled.
Makes sense to me. Thanks Jim.
--
paul moore
www.paul-moore.com
next prev parent reply other threads:[~2020-12-10 2:41 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 14:42 virtiofs and its optional xattr support vs. fs_use_xattr Ondrej Mosnacek
2020-12-07 15:03 ` Paul Moore
2020-12-07 20:52 ` Vivek Goyal
2020-12-07 21:22 ` Dominick Grift
2020-12-08 14:33 ` Vivek Goyal
2020-12-08 15:13 ` Dominick Grift
2020-12-08 23:41 ` Paul Moore
2020-12-07 17:17 ` James Carter
2020-12-08 23:45 ` Paul Moore
2020-12-09 15:37 ` James Carter
2020-12-10 2:39 ` Paul Moore [this message]
2020-12-10 9:29 ` Ondrej Mosnacek
2020-12-10 22:17 ` Vivek Goyal
2020-12-10 22:24 ` Ondrej Mosnacek
2020-12-10 22:30 ` Vivek Goyal
2020-12-11 9:15 ` Ondrej Mosnacek
2020-12-11 13:29 ` Vivek Goyal
2021-01-04 20:14 ` Vivek Goyal
2021-01-05 14:00 ` Ondrej Mosnacek
2021-01-05 14:21 ` Vivek Goyal
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