Quoting Andrei Vagin (avagin@xxxxxxxxxx):
> From: Andrey Vagin <avagin@xxxxxxxxxx>
>
> Pid and user namepaces are hierarchical. There is no way to discover
> parent-child relationships.
>
> In a future we will use this interface to dump and restore nested
> namespaces.
>
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
> ---
> fs/nsfs.c | 4 ++++
> include/linux/proc_ns.h | 1 +
> include/uapi/linux/nsfs.h | 2 ++
> kernel/pid_namespace.c | 19 +++++++++++++++++++
> kernel/user_namespace.c | 1 +
> 5 files changed, 27 insertions(+)
>
> diff --git a/fs/nsfs.c b/fs/nsfs.c
> index be7d193..11a4b15 100644
> --- a/fs/nsfs.c
> +++ b/fs/nsfs.c
> @@ -170,6 +170,10 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
> switch (ioctl) {
> case NS_GET_USERNS:
> return open_related_ns(ns, ns_get_owner);
> + case NS_GET_PARENT:
> + if (!ns->ops->get_parent)
> + return -EINVAL;
> + return open_related_ns(ns, ns->ops->get_parent);
> default:
> return -ENOTTY;
> }
> diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
> index ca85a43..12cb8bd 100644
> --- a/include/linux/proc_ns.h
> +++ b/include/linux/proc_ns.h
> @@ -19,6 +19,7 @@ struct proc_ns_operations {
> void (*put)(struct ns_common *ns);
> int (*install)(struct nsproxy *nsproxy, struct ns_common *ns);
> struct user_namespace *(*owner)(struct ns_common *ns);
> + struct ns_common *(*get_parent)(struct ns_common *ns);
> };
>
> extern const struct proc_ns_operations netns_operations;
> diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
> index 5cacd5c..3af6172 100644
> --- a/include/uapi/linux/nsfs.h
> +++ b/include/uapi/linux/nsfs.h
> @@ -7,5 +7,7 @@
>
> /* Returns a file descriptor that refers to an owning user namespace */
> #define NS_GET_USERNS _IO(NSIO, 0x1)
> +/* Returns a file descriptor that refers to a parent namespace */
> +#define NS_GET_PARENT _IO(NSIO, 0x2)
>
> #endif /* __LINUX_NSFS_H */
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index c18f0f4f..aad470b 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -405,6 +405,24 @@ static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
> return 0;
> }
>
> +static struct ns_common *pidns_get_parent(struct ns_common *ns)
> +{
> + struct pid_namespace *active = task_active_pid_ns(current);
> + struct pid_namespace *pid_ns, *p;
> +
> + /* See if the parent is in the current namespace */
> + pid_ns = p = to_pid_ns(ns)->parent;
> + for (;;) {
> + if (!p)
> + return ERR_PTR(-EPERM);
> + if (p == active)
> + break;
> + p = p->parent;
> + }
> +
> + return &get_pid_ns(pid_ns)->ns;
> +}
> +
> static struct user_namespace *pidns_owner(struct ns_common *ns)
> {
> return to_pid_ns(ns)->user_ns;
> @@ -417,6 +435,7 @@ const struct proc_ns_operations pidns_operations = {
> .put = pidns_put,
> .install = pidns_install,
> .owner = pidns_owner,
> + .get_parent = pidns_get_parent,
> };
>
> static __init int pid_namespaces_init(void)
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 42a64d5..33b523c 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -1080,6 +1080,7 @@ const struct proc_ns_operations userns_operations = {
> .put = userns_put,
> .install = userns_install,
> .owner = userns_owner,
> + .get_parent = ns_get_owner,
> };
>
> static __init int user_namespaces_init(void)
> --
> 2.5.5
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