Seth Forshee [off-list ref] writes:

On Mon, Jan 04, 2016 at 12:03:39PM -0600, Seth Forshee wrote:

quoted

These patches implement support for mounting filesystems in user
namespaces using fuse. They are based on the patches in the for-testing
branch of
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git,
but I've rebased them onto 4.4-rc3. I've pushed all of this to:

 git://git.kernel.org/pub/scm/linux/kernel/git/sforshee/linux.git fuse-userns

The patches are organized into three high-level groups.

Patches 1-6 are related to security, adding restrictions for
unprivileged mounts and updating the LSMs as needed. Patches 1-2
(checking inode permissions for block device mounts) may not be strictly
necessary for fuseblk mounts since fuse doesn't do any IO on the block
device in the kernel, but it still seems like a good idea to fail the
mount if the user doesn't have the required permissions for the inode
(though this is a bit misleading with fuse since the mounts are done via
a suid-root helper).

Patches 7-14 update most of the vfs to translate ids correctly and deal
with inodes which may have invalid user/group ids. I've omitted patches
for anything not used by fuse - quota, fs freezing, some helper
functions, etc. - but if these are wanted for the sake of completeness I
can include them.

Patches 15-18 update fuse to deal with mounts from non-init pid and user
namespaces and enable mounting from user namespaces.

Changes since v1:
 - Drop patch for FIBMAP.
 - Use current_in_userns in fuse_allow_current_process.
 - Remove checks for uid/gid validity in fuse. Intead, ids from the
   backing store which do not map into s_user_ns will result in invalid
   ids in the vfs inode. Checks in the vfs will prevent unmappable ids
   from being passed in from above.
 - Update a couple of commit messages to provide more detail about
   changes.

Now that the merge window is over, I'm wondering whether it might be
possible to get some feedback on these patches this cycle?

Definitely.  Apologies for not giving you much feedback earlier.

I had been hoping this was the kind of thing I could just double check
to be certain you weren't doing anything silly and just apply.  After my
last round of looking at this I realized that for me to be comfortable
with these patches I will have to give them very close scrutiny, and
check every detail.

Unfortunatly last cycle I had failed to budget enough time to give these
patches the close scrutiny they need.

From a high level I am still very much in favor of this approach and
at least getting as far as safe unprivileged fuse mounts.

I have one or two little things to look at and then I hope to be going
through your patches one by one in detail.

Eric