root/kernel/user_namespace.c

DEFINITIONS

1. clone_user_ns
2. copy_user_ns
3. free_user_ns

/*
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License as
 *  published by the Free Software Foundation, version 2 of the
 *  License.
 */

#include <linux/module.h>
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>

/*
 * Clone a new ns copying an original user ns, setting refcount to 1
 * @old_ns: namespace to clone
 * Return NULL on error (failure to kmalloc), new ns otherwise
 */
static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
{
        struct user_namespace *ns;
        struct user_struct *new_user;
        int n;

        ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
        if (!ns)
                return ERR_PTR(-ENOMEM);

        kref_init(&ns->kref);

        for (n = 0; n < UIDHASH_SZ; ++n)
                INIT_HLIST_HEAD(ns->uidhash_table + n);

        /* Insert new root user.  */
        ns->root_user = alloc_uid(ns, 0);
        if (!ns->root_user) {
                kfree(ns);
                return ERR_PTR(-ENOMEM);
        }

        /* Reset current->user with a new one */
        new_user = alloc_uid(ns, current->uid);
        if (!new_user) {
                free_uid(ns->root_user);
                kfree(ns);
                return ERR_PTR(-ENOMEM);
        }

        switch_uid(new_user);
        return ns;
}

struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
{
        struct user_namespace *new_ns;

        BUG_ON(!old_ns);
        get_user_ns(old_ns);

        if (!(flags & CLONE_NEWUSER))
                return old_ns;

        new_ns = clone_user_ns(old_ns);

        put_user_ns(old_ns);
        return new_ns;
}

void free_user_ns(struct kref *kref)
{
        struct user_namespace *ns;

        ns = container_of(kref, struct user_namespace, kref);
        release_uids(ns);
        kfree(ns);
}
EXPORT_SYMBOL(free_user_ns);