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From:   Dongsu Park <dongsu@kinvolk.io>
Date:   Tue, 29 May 2018 17:40:50 +0200
Message-ID: <CANxcAMt5f7=TV3Yqc6iavos=saGFOPKC4R4Yr9yGbKoVwq3YGw@mail.gmail.com>
Subject: Re: [REVIEW][PATCH 0/6] Wrapping up the vfs support for unprivileged mounts
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Linux Containers <containers@lists.linux-foundation.org>,
        linux-fsdevel@vger.kernel.org,
        Seth Forshee <seth.forshee@canonical.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Christian Brauner <christian@brauner.io>
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Hi,

On Thu, May 24, 2018 at 1:22 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> Very slowly the work has been progressing to ensure the vfs has the
> necessary support for mounting filesystems without privilege.
>
> This patchset contains one more core piece of that work, ensuring a few
> more operations that would write back an inode and confuse an exisiting
> filesystem are denied.
>
> The rest of the changes actually enable userns root to do things with
> filesystems that the userns root has mounted.  Most of these have been
> waiting in the wings a long time, held back because I wanted the core
> of the patchset to be solid before I started allowing additional
> behavor.
>
> It is definitely time for these changes so the effect of s_user_ns
> becomes less theoretical.
>
> The change to allow mknod is new, but consistent with everything else
> and harmless as device nodes on filesystems mounted without privilege
> are ignored.
>
> Unless problems show up in the during review I plan to merge these changes.

Thank you for the great work. I have been looking forward to seeing it.
I have just gathered available relevant patches in my branch:

https://github.com/kinvolk/linux/tree/dongsu/fuse-userns-for-4.18

With this branch, I tested sshfs/fuse from non-init user namespace.
It works fine as expected. So you can add:

Tested-by: Dongsu Park <dongsu@kinvolk.io>

Thanks!
Dongsu

> These changes are also available at:
>   git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git userns-test
>
> Eric W. Biederman (5):
>       vfs: Don't allow changing the link count of an inode with an invalid uid or gid
>       vfs: Allow userns root to call mknod on owned filesystems.
>       fs: Allow superblock owner to replace invalid owners of inodes
>       fs: Allow superblock owner to access do_remount_sb()
>       capabilities: Allow privileged user in s_user_ns to set security.* xattrs
>
> Seth Forshee (1):
>       fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems
>
>  fs/attr.c            | 36 ++++++++++++++++++++++++++++--------
>  fs/ioctl.c           |  4 ++--
>  fs/namei.c           | 16 ++++++++++++----
>  fs/namespace.c       |  4 ++--
>  security/commoncap.c |  8 ++++++--
>  5 files changed, 50 insertions(+), 18 deletions(-)
>
> Eric
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