SELinux labels not defined

[Gao Xiang]

Hi,

On Mon, Oct 04, 2021 at 09:44:49AM +0800, Gao Xiang wrote:
> On Sun, Oct 03, 2021 at 08:31:18PM -0400, David Michael wrote:
> > On Sun, Oct 3, 2021 at 12:38 AM Gao Xiang <xiang at kernel.org> wrote:
> > > Hi David,
> > >
> > > On Sat, Oct 02, 2021 at 06:50:55PM -0400, David Michael wrote:
> > > > Hi,
> > > >
> > > > I tried to make an SELinux-labeled EROFS image, and the image itself
> > > > seems to contain the labels from a hex dump, but the mounted files are
> > > > all unlabeled:
> > > >
> > > > # ls -lZ xml
> > > > total 8
> > > > drwxr-xr-x. 2 root root unconfined_u:object_r:var_t:s0         4096 Sep 29 21:43 dbus-1
> > > > drwxr-xr-x. 2 root root unconfined_u:object_r:fonts_cache_t:s0 4096 Sep 29 22:19 fontconfig
> > > > # mkfs.erofs test.img xml
> > > > mkfs.erofs 1.3-g4e183568-dirty
> > > >       c_version:           [1.3-g4e183568-dirty]
> > > >       c_dbg_lvl:           [       2]
> > > >       c_dry_run:           [       0]
> > > > # mount -o X-mount.mkdir test.img test
> > > > # ls -lZ test
> > > > total 8
> > > > drwxr-xr-x. 2 root root system_u:object_r:unlabeled_t:s0 78 Oct  2 18:37 dbus-1
> > > > drwxr-xr-x. 2 root root system_u:object_r:unlabeled_t:s0 48 Oct  2 18:37 fontconfig
> > > >
> > > > This is running on the current Fedora kernel 5.14.9-200.fc34.x86_64 with
> > > > the relevant config options:
> > > >
> > > > CONFIG_EROFS_FS=m
> > > > # CONFIG_EROFS_FS_DEBUG is not set
> > > > CONFIG_EROFS_FS_XATTR=y
> > > > CONFIG_EROFS_FS_POSIX_ACL=y
> > > > CONFIG_EROFS_FS_SECURITY=y
> > > > CONFIG_EROFS_FS_ZIP=y
> > > >
> > > > I tried the earliest kernel in Fedora 34 (5.11.12-300.fc34.x86_64), and
> > > > it also has the same issue.  However, the earliest kernel in Fedora 33
> > > > (5.8.15-301.fc33.x86_64) has the correct labels when the image is
> > > > mounted.  Is there a problem in the file system driver, or do I need to
> > > > do something different for newer kernels?
> > >
> > > Thanks for your report!
> > >
> > > I don't think there is any difference between 5.8 - 5.14 on EROFS selinux
> > > xattrs. And AFAIK some users already use EROFS selinux on Linux 5.10.
> > >
> > > Would you mind checking if Fedora kernels did something new for EROFS or
> > > something else on fc34? Can you check if the images work on upstream
> > > kernels?
> > 
> > The labels failed in the same way on every distro I tried: Fedora,
> > openSUSE (5.14.6-1.4.x86_64), Ubuntu (5.11.0-37-generic), and Gentoo
> > (5.14.8-gentoo-dist-hardened and 5.10.68-gentoo-dist-hardened).
> > 
> > I noticed that the labels appear correctly when the system is running
> > with SELinux disabled, but booting with it enabled results in
> > unlabeled_t labels on erofs mounts.
> 
> May I ask what "getfattr -m security.selinux" returns for these files if
> the issue happens?
> 
> I have no idea what's wrong with the recent versions. I'll dig info it
> further. But it needs some extra time.

I found SECURITY_FS_USE_XATTR was not set due to lack of proper
sepolicy. I've sent out a patch to refpolicy to address this:
https://lore.kernel.org/selinux-refpolicy/20211004035901.5428-1-xiang@kernel.org/

Actually Android has its own sepolicy and doesn't use refpolicy
above. We updated it several years ago. But refpolicy seems not.

As for why Fedora 33 works, I have no clue yet (don't have much
time on digging this.)

Thanks,
Gao Xiang