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

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Date:   Wed, 5 Dec 2018 10:37:56 +0100
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-next@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, selinux@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: linux-next: manual merge of the selinux tree with the vfs tree

On Mon, Dec 3, 2018 at 10:56 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> On Mon, Dec 03, 2018 at 11:12:59AM +0100, Ondrej Mosnacek wrote:
>
> > I think I figured out what's the problem. NFS still creates the
> > submount via the old vfs_submount() call, which calls
> > vfs_kern_mount(), which creates an fs_context with
> > FS_CONTEXT_FOR_USER_MOUNT because FS_CONTEXT_FOR_SUBMOUNT needs the
> > mountpoint dentry reference and there is currently no way to pass that
> > to vfs_kern_mount(). This is further complicated by the fact that
> > vfs_submount() accepts only a const reference to the mountpoint, while
> > vfs_new_fs_context() expects a non-const one...
> >
> > I think all users of the old vfs_submount call should be converted to
> > the new API before the VFS changes are merged into mainline, otherwise
> > they will break the SELinux submount fix. We could work around it in
> > the SELinux hook by checking the fc->sb_flags[_mask] for SB_SUBMOUNT,
> > but I guess that would be a hack.
>
> Could you take a look at vfs.git#Q28?  There's still a massive reshuffling
> going on, so there will be more branches; this one is the latest at the
> moment.

I just tested the Q28 branch rebased onto a recent Fedora rawhide
kernel (4.20.0-0.rc5.git0.1) and that code seems to be working fine.
The submount test failed with Q28 and succeeds with Q28+fix, as
expected. Also, the overlay tests failures are gone now (except for
the 4 known failures from GH issue #43, since I had to rebase onto
4.20-rcX).

This is the commit that I used as the SELinux submount fix:
https://gitlab.com/omos/linux-public/commit/47922f9c70a83008388b836c285f94c40da1af2b

Kernel builds:
Unfixed Q28:  https://copr.fedorainfracloud.org/coprs/omos/kernel-testing/build/833311/
Fixed Q28:  https://copr.fedorainfracloud.org/coprs/omos/kernel-testing/build/833312/

Selinux-testsuite reports:
=== Q28 ===
Test Summary Report
-------------------
overlay/test              (Wstat: 1024 Tests: 119 Failed: 4)
  Failed tests:  81, 83, 107, 112
  Non-zero exit status: 4
submount/test             (Wstat: 256 Tests: 2 Failed: 1)
  Failed test:  2
  Non-zero exit status: 1
Files=54, Tests=615, 117 wallclock secs ( 0.20 usr  0.04 sys +  1.64
cusr  1.29 csys =  3.17 CPU)
Result: FAIL
Failed 2/54 test programs. 5/615 subtests failed.

=== Q28 + FIX ===
Test Summary Report
-------------------
overlay/test              (Wstat: 1024 Tests: 119 Failed: 4)
  Failed tests:  81, 83, 107, 112
  Non-zero exit status: 4
Files=54, Tests=615, 117 wallclock secs ( 0.22 usr  0.05 sys +  1.54
cusr  1.37 csys =  3.18 CPU)
Result: FAIL
Failed 1/54 test programs. 4/615 subtests failed.

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