linux/kernel/user_namespace.c
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   1/*
   2 *  This program is free software; you can redistribute it and/or
   3 *  modify it under the terms of the GNU General Public License as
   4 *  published by the Free Software Foundation, version 2 of the
   5 *  License.
   6 */
   7
   8#include <linux/module.h>
   9#include <linux/nsproxy.h>
  10#include <linux/slab.h>
  11#include <linux/user_namespace.h>
  12
  13/*
  14 * Clone a new ns copying an original user ns, setting refcount to 1
  15 * @old_ns: namespace to clone
  16 * Return NULL on error (failure to kmalloc), new ns otherwise
  17 */
  18static struct user_namespace *clone_user_ns(struct user_namespace *old_ns)
  19{
  20        struct user_namespace *ns;
  21        struct user_struct *new_user;
  22        int n;
  23
  24        ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
  25        if (!ns)
  26                return ERR_PTR(-ENOMEM);
  27
  28        kref_init(&ns->kref);
  29
  30        for (n = 0; n < UIDHASH_SZ; ++n)
  31                INIT_HLIST_HEAD(ns->uidhash_table + n);
  32
  33        /* Insert new root user.  */
  34        ns->root_user = alloc_uid(ns, 0);
  35        if (!ns->root_user) {
  36                kfree(ns);
  37                return ERR_PTR(-ENOMEM);
  38        }
  39
  40        /* Reset current->user with a new one */
  41        new_user = alloc_uid(ns, current->uid);
  42        if (!new_user) {
  43                free_uid(ns->root_user);
  44                kfree(ns);
  45                return ERR_PTR(-ENOMEM);
  46        }
  47
  48        switch_uid(new_user);
  49        return ns;
  50}
  51
  52struct user_namespace * copy_user_ns(int flags, struct user_namespace *old_ns)
  53{
  54        struct user_namespace *new_ns;
  55
  56        BUG_ON(!old_ns);
  57        get_user_ns(old_ns);
  58
  59        if (!(flags & CLONE_NEWUSER))
  60                return old_ns;
  61
  62        new_ns = clone_user_ns(old_ns);
  63
  64        put_user_ns(old_ns);
  65        return new_ns;
  66}
  67
  68void free_user_ns(struct kref *kref)
  69{
  70        struct user_namespace *ns;
  71
  72        ns = container_of(kref, struct user_namespace, kref);
  73        release_uids(ns);
  74        kfree(ns);
  75}
  76EXPORT_SYMBOL(free_user_ns);
  77