Re: linux-next: manual merge of the selinux tree with the vfs tree

[Ondrej Mosnacek]

On Thu, Nov 29, 2018 at 11:07 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> On Wed, Nov 28, 2018 at 10:52 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> > On Tue, Nov 27, 2018 at 6:50 AM Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
> > > Hi Ondrej,
> > >
> > > On Tue, 27 Nov 2018 09:53:32 +0100 Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> > > >
> > > > Hm... seems that there was some massive overhaul in the VFS code right
> > > > at the wrong moment... There are new hooks for mounting now and the
> > >
> > > The mount changes have been in linux-next since before the last
> > > release ...
> > >
> > > > code that our commit changes is now here:
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/tree/security/selinux/hooks.c?h=for-next#n3131
> > > >
> > > > It seems that the logic is still the same, just now our patch (or the
> > > > VFS one) needs to be updated to change the above line as such
> > > > (untested pseudo-patch):
> > > >
> > > > - if (fc->purpose == FS_CONTEXT_FOR_KERNEL_MOUNT)
> > > > + if (fc->purpose == (FS_CONTEXT_FOR_KERNEL_MOUNT|FS_CONTEXT_FOR_SUBMOUNT))
> > >
> > > OK, so from tomorrow I will use that merge resolution.  Someone needs
> > > to remember to tell Linus about this when the latter of the vfs and
> > > selinux trees reach him.
> >
> > I will, or at least I'll do my best to remember; since we only have a
> > few more week until the merge window I like my odds.  FWIW, I
> > typically do a test merge on top of Linus' tree before sending the
> > SELinux PR just to verify that everything is relatively clean and
> > there are no surprises.
> >
> > Ondrej, please work with David Howells to ensure that submounts are
> > handled correctly in his mount rework.
>
> OK, I will verify that the SELinux submount fix rebased on top of
> vfs/work.mount in the way I suggested above passes the same testing
> (seliinux-testsuite + NFS crossmnt reproducer). I am now building two
> kernels (vfs/work.mount with and without the fix) to test. Let me know
> if there is anything more to do.

I tested the proposed patch ([1]; fixed as per correction from David
Howells) applied on top of patches v4.19-rc3..vfs/work.mount applied
on top of the 4.19.5-300 Fedora 29 kernel.

However, the submount test was still failing, so I looked again at the
list of the possible 'purpose' values and it turns out the value used
by NFS et al. is actually FS_CONTEXT_FOR_ROOT_MOUNT (it is actually
documented nicely in Documentation/filesystems/mount_api.txt). So I'll
need to build a new test kernel with updated patch ([2]) and retest...

BTW, the vfs/work.mount changes alone seem to cause some overlay test
failures (I didn't test a clean 4.19.5 so it may be due to some stable
patch as well):

Test Summary Report
-------------------
overlay/test              (Wstat: 3072 Tests: 119 Failed: 12)
 Failed tests:  66, 74, 76-77, 79, 87, 95, 103, 108, 110-111
               117
 Non-zero exit status: 12

The failing tests are all in the context mount section, but I don't
think this is (directly) related to [3] because there are much more
tests failing and the kernel I was testing didn't include the
problematic OverlayFS patch. Perhaps the VFS patches somehow broke the
parsing of the context= mount option?

[1] https://gitlab.com/omos/linux-public/commit/fe5478717ddde92e3ea599e14051ad57522fdf47
[2] https://gitlab.com/omos/linux-public/commit/f5c58adc7babd62e4bfe8cda799459d263dc5186
[3] https://github.com/SELinuxProject/selinux-kernel/issues/43

--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.