Re: [PATCH 0/7] Initial support for user namespace owned mounts

Casey Schaufler
2015-07-15T20:36:29Z

On 7/15/2015 12:46 PM, Seth Forshee wrote:
> These are the first in a larger set of patches that I've been working on
> (with help from Eric Biederman) to support mounting ext4 and fuse
> filesystems from within user namespaces. I've pushed the full series to:
>
> git://kernel.ubuntu.com/sforshee/linux.git userns-mounts
>
> Taking the series as a whole, the strategy is to handle as much of the
> heavy lifting as possible in the vfs so the filesystems don't have to
> handle weird edge cases. If you look at the full series you'll find that
> the changes in ext4 to support user namespace mounts turn out to be
> fairly minimal (fuse is a bit more complicated though as it must deal
> with translating ids for a userspace process which is running in pid and
> user namespaces).
>
> The patches I'm sending today lay some of the groundwork in the vfs and
> related code. They fall into two broad groups:
>
> 1. Patches 1-2 add s_user_ns and simplify MNT_NODEV handling. These are
> pretty straightforward, and Eric has expressed interest in merging
> these patches soon. Note that patch 2 won't apply cleanly without
> Eric's noexec patches for proc and sys [1].
>
> 2. Patches 2-7 tighten down security for mounts with s_user_ns !=
> &init_user_ns. This includes updates to how file caps and suid are
> handled and LSM updates to ignore security labels on superblocks
> from non-init namespaces.
>
> The LSM changes in particular may not be optimal, as I don't have a
> lot of familiarity with this code, so I'd be especially appreciative
> of review of these changes and suggestions on how to improve them.

Lukasz Pawelczyk <l.pawelczyk@samsung.com> proposed
LSM support in user namespaces ([RFC] lsm: namespace hooks)
that make a whole lot more sense than just turning off
the option of using labels on files. Gutting the ability
to use MAC in a namespace is a step down the road of
making MAC and namespaces incompatible.

>
> Subsequent patches will update the vfs for id translation, handling
> various corner cases, giving privileges to the user namsepace which owns
> a superblock, and finally supporting user namespace mounts for ext4 and
> fuse.
>
> Thanks,
> Seth
>
> [1] http://lkml.kernel.org/r/87mvz4yomp.fsf_-_@x220.int.ebiederm.org
>
>
> Andy Lutomirski (1):
> fs: Treat foreign mounts as nosuid
>
> Eric W. Biederman (1):
> userns: Simpilify MNT_NODEV handling.
>
> Seth Forshee (5):
> fs: Add user namesapace member to struct super_block
> fs: Ignore file caps in mounts from other user namespaces
> security: Restrict security attribute updates for userns mounts
> selinux: Ignore security labels on user namespace mounts
> smack: Don't use security labels for user namespace mounts
>
> fs/block_dev.c | 2 +-
> fs/exec.c | 2 +-
> fs/namei.c | 9 ++++++++-
> fs/namespace.c | 34 ++++++++++++++++++++--------------
> fs/proc/root.c | 3 ++-
> fs/super.c | 38 +++++++++++++++++++++++++++++++++-----
> include/linux/fs.h | 9 +++++++++
> include/linux/mount.h | 1 +
> include/linux/user_namespace.h | 8 ++++++++
> kernel/user_namespace.c | 14 ++++++++++++++
> security/commoncap.c | 4 +++-
> security/security.c | 10 +++++++++-
> security/selinux/hooks.c | 16 +++++++++++++++-
> security/smack/smack_lsm.c | 12 ++++++++++--
> 14 files changed, 134 insertions(+), 28 deletions(-)
>
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