kernel/user_namespace.c

   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  */
  23 int 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  */
  69 static 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
  77 void 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 }
  85 EXPORT_SYMBOL(free_user_ns);
  86
  87 uid_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
 109 gid_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 }