Re: [PATCH -mm 5/7] add user namespace

[Eric W. Biederman]

Cedric Le Goater <clg@xxxxxxxxxx> writes:

> This patch adds the user namespace.
>
> Basically, it allows a process to unshare its user_struct table,
> resetting at the same time its own user_struct and all the associated
> accounting.
>
> For the moment, the root_user is added to the new user namespace when
> it is cloned. An alternative behavior would be to let the system
> allocate a new user_struct(0) in each new user namespace. However,
> these 0 users would not have the privileges of the root_user and it
> would be necessary to work on the process capabilities to give them
> some permissions.

It is completely the wrong thing for a the root_user to span multiple
namespaces as you describe.  It is important for uid 0 in other namespaces
to not have the privileges of the root_user.  That is half the point.

Too many files in sysfs and proc don't require caps but instead simply
limit things to uid 0.  Having a separate uid 0 in the different namespaces
instantly makes all of these files inaccessible, and keeps processes from
doing something bad.

To a filesystem a uid does not share a uid namespace with the only things
that should be accessible are those things that are readable/writeable
by everyone.   Unless the filesystem has provisions for storing multiple
uid namespaces not files should be able to be created.  Think NFS root
squash.

> Signed-off-by: Cedric Le Goater <clg@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxx>
> Cc: Kirill Korotaev <dev@xxxxxxxxxx>
> Cc: Andrey Savochkin <saw@xxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Herbert Poetzl <herbert@xxxxxxxxxxxx>
> Cc: Sam Vilain <sam.vilain@xxxxxxxxxxxxxxx>
> Cc: Serge E. Hallyn <serue@xxxxxxxxxx>
> Cc: Dave Hansen <haveblue@xxxxxxxxxx>
>
> ---
>  fs/ioprio.c               |    5 +
>  include/linux/init_task.h |    2 
>  include/linux/nsproxy.h   |    2 
>  include/linux/sched.h     |    6 +-
>  include/linux/user.h      |   45 +++++++++++++++
>  init/Kconfig              |    8 ++
>  kernel/nsproxy.c          |   15 ++++-
>  kernel/sys.c              |    8 +-
>  kernel/user.c | 135 ++++++++++++++++++++++++++++++++++++++++++----

This patch looks extremly incomplete.

Every comparison of a user id needs to compare the tuple
(user namespace, user id) or it needs to compare struct users.

Ever comparison of a group id needs to compare the tuple
(user namespace, group id) or it needs to compare struct users.

I think the key infrastructure needs to be looked at here as well.

There needs to be a user namespace association for mounted filesystems.

We need a discussion about how we handle map users from one user
namespace to another, because without some form of mapping so many
things become inaccessible that the system is almost useless.

I believe some of the key infrastructure which is roughly kerberos
authentication tokens could be used for this purpose.

A user namespace is a big thing.  What I see here doesn't even
seem to scratch the surface.

Eric

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