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#include <linux/highuid.h>
  13#include <linux/cred.h>
  14
  15static struct kmem_cache *user_ns_cachep __read_mostly;
  16
  17/*
  18 * Create a new user namespace, deriving the creator from the user in the
  19 * passed credentials, and replacing that user with the new root user for the
  20 * new namespace.
  21 *
  22 * This is called by copy_creds(), which will finish setting the target task's
  23 * credentials.
  24 */
  25int create_user_ns(struct cred *new)
  26{
  27        struct user_namespace *ns;
  28        struct user_struct *root_user;
  29        int n;
  30
  31        ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
  32        if (!ns)
  33                return -ENOMEM;
  34
  35        kref_init(&ns->kref);
  36
  37        for (n = 0; n < UIDHASH_SZ; ++n)
  38                INIT_HLIST_HEAD(ns->uidhash_table + n);
  39
  40        /* Alloc new root user.  */
  41        root_user = alloc_uid(ns, 0);
  42        if (!root_user) {
  43                kmem_cache_free(user_ns_cachep, ns);
  44                return -ENOMEM;
  45        }
  46
  47        /* set the new root user in the credentials under preparation */
  48        ns->creator = new->user;
  49        new->user = root_user;
  50        new->uid = new->euid = new->suid = new->fsuid = 0;
  51        new->gid = new->egid = new->sgid = new->fsgid = 0;
  52        put_group_info(new->group_info);
  53        new->group_info = get_group_info(&init_groups);
  54#ifdef CONFIG_KEYS
  55        key_put(new->request_key_auth);
  56        new->request_key_auth = NULL;
  57#endif
  58        /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
  59
  60        /* root_user holds a reference to ns, our reference can be dropped */
  61        put_user_ns(ns);
  62
  63        return 0;
  64}
  65
  66/*
  67 * Deferred destructor for a user namespace.  This is required because
  68 * free_user_ns() may be called with uidhash_lock held, but we need to call
  69 * back to free_uid() which will want to take the lock again.
  70 */
  71static void free_user_ns_work(struct work_struct *work)
  72{
  73        struct user_namespace *ns =
  74                container_of(work, struct user_namespace, destroyer);
  75        free_uid(ns->creator);
  76        kmem_cache_free(user_ns_cachep, ns);
  77}
  78
  79void free_user_ns(struct kref *kref)
  80{
  81        struct user_namespace *ns =
  82                container_of(kref, struct user_namespace, kref);
  83
  84        INIT_WORK(&ns->destroyer, free_user_ns_work);
  85        schedule_work(&ns->destroyer);
  86}
  87EXPORT_SYMBOL(free_user_ns);
  88
  89uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
  90{
  91        struct user_namespace *tmp;
  92
  93        if (likely(to == cred->user->user_ns))
  94                return uid;
  95
  96
  97        /* Is cred->user the creator of the target user_ns
  98         * or the creator of one of it's parents?
  99         */
 100        for ( tmp = to; tmp != &init_user_ns;
 101              tmp = tmp->creator->user_ns ) {
 102                if (cred->user == tmp->creator) {
 103                        return (uid_t)0;
 104                }
 105        }
 106
 107        /* No useful relationship so no mapping */
 108        return overflowuid;
 109}
 110
 111gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
 112{
 113        struct user_namespace *tmp;
 114
 115        if (likely(to == cred->user->user_ns))
 116                return gid;
 117
 118        /* Is cred->user the creator of the target user_ns
 119         * or the creator of one of it's parents?
 120         */
 121        for ( tmp = to; tmp != &init_user_ns;
 122              tmp = tmp->creator->user_ns ) {
 123                if (cred->user == tmp->creator) {
 124                        return (gid_t)0;
 125                }
 126        }
 127
 128        /* No useful relationship so no mapping */
 129        return overflowgid;
 130}
 131
 132static __init int user_namespaces_init(void)
 133{
 134        user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
 135        return 0;
 136}
 137module_init(user_namespaces_init);
 138
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