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SubjectRe: [PATCH 02/14] allow root in container to copy namespaces
Serge Hallyn <serge@hallyn.com> writes:

> From: Serge E. Hallyn <serge.hallyn@canonical.com>
>
> Othewise nested containers with user namespaces won't be possible.
>
> It's true that user namespaces are not yet fully isolated, but for
> that same reason there are far worse things that root in a child
> user ns can do. Spawning a child user ns is not in itself bad.
>
> This patch also allows setns for root in a container:
> @Eric Biederman: are there gotchas in allowing setns from child
> userns?

Yes. We need to ensure that the target namespaces are namespaces
that have been created in from user_namespace or from a child of this
user_namespace.

Aka we need to ensure that we have CAP_SYS_ADMIN for the new namespace.

Eric

> Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> ---
> kernel/fork.c | 4 ++--
> kernel/nsproxy.c | 6 +++---
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 17bf7c8..22d0cf0 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1473,8 +1473,8 @@ long do_fork(unsigned long clone_flags,
> /* hopefully this check will go away when userns support is
> * complete
> */
> - if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
> - !capable(CAP_SETGID))
> + if (!nsown_capable(CAP_SYS_ADMIN) || !nsown_capable(CAP_SETUID) ||
> + !nsown_capable(CAP_SETGID))
> return -EPERM;
> }
>
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index 9aeab4b..f50542d 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -134,7 +134,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> CLONE_NEWPID | CLONE_NEWNET)))
> return 0;
>
> - if (!capable(CAP_SYS_ADMIN)) {
> + if (!nsown_capable(CAP_SYS_ADMIN)) {
> err = -EPERM;
> goto out;
> }
> @@ -191,7 +191,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
> CLONE_NEWNET)))
> return 0;
>
> - if (!capable(CAP_SYS_ADMIN))
> + if (!nsown_capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> *new_nsp = create_new_namespaces(unshare_flags, current,
> @@ -241,7 +241,7 @@ SYSCALL_DEFINE2(setns, int, fd, int, nstype)
> struct file *file;
> int err;
>
> - if (!capable(CAP_SYS_ADMIN))
> + if (!nsown_capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> file = proc_ns_fget(fd);


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