[REVIEW][PATCH 0/6] Wrapping up the vfs support for unprivileged mounts

Dongsu Park dongsu at kinvolk.io
Tue May 29 15:40:50 UTC 2018


On Thu, May 24, 2018 at 1:22 AM, Eric W. Biederman
<ebiederm at 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:


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 at kinvolk.io>


> 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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