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