ns: proc files for namespace naming policy.

Create files under /proc/<pid>/ns/ to allow controlling the
namespaces of a process.

This addresses three specific problems that can make namespaces hard to
work with.
- Namespaces require a dedicated process to pin them in memory.
- It is not possible to use a namespace unless you are the child
  of the original creator.
- Namespaces don't have names that userspace can use to talk about
  them.

The namespace files under /proc/<pid>/ns/ can be opened and the
file descriptor can be used to talk about a specific namespace, and
to keep the specified namespace alive.

A namespace can be kept alive by either holding the file descriptor
open or bind mounting the file someplace else.  aka:
mount --bind /proc/self/ns/net /some/filesystem/path
mount --bind /proc/self/fd/<N> /some/filesystem/path

This allows namespaces to be named with userspace policy.

It requires additional support to make use of these filedescriptors
and that will be comming in the following patches.

Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 838c1149251a..a6d2c6da5e5a 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -179,6 +179,8 @@ extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
 extern struct file *get_mm_exe_file(struct mm_struct *mm);
 extern void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm);
 
+extern struct file *proc_ns_fget(int fd);
+
 #else
 
 #define proc_net_fops_create(net, name, mode, fops)  ({ (void)(mode), NULL; })
@@ -239,6 +241,11 @@ static inline void dup_mm_exe_file(struct mm_struct *oldmm,
                                    struct mm_struct *newmm)
 {}
 
+static inline struct file *proc_ns_fget(int fd)
+{
+        return ERR_PTR(-EINVAL);
+}
+
 #endif /* CONFIG_PROC_FS */
 
 #if !defined(CONFIG_PROC_KCORE)
@@ -250,6 +257,15 @@ kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 extern void kclist_add(struct kcore_list *, void *, size_t, int type);
 #endif
 
+struct nsproxy;
+struct proc_ns_operations {
+        const char *name;
+        int type;
+        void *(*get)(struct task_struct *task);
+        void (*put)(void *ns);
+        int (*install)(struct nsproxy *nsproxy, void *ns);
+};
+
 union proc_op {
         int (*proc_get_link)(struct inode *, struct path *);
         int (*proc_read)(struct task_struct *task, char *page);
@@ -268,6 +284,8 @@ struct proc_inode {
         struct proc_dir_entry *pde;
         struct ctl_table_header *sysctl;
         struct ctl_table *sysctl_entry;
+        void *ns;
+        const struct proc_ns_operations *ns_ops;
         struct inode vfs_inode;
 };