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/export.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 static 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  */
  25 int 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  */
  71 static 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
  79 void 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 }
  87 EXPORT_SYMBOL(free_user_ns);
  88
  89 uid_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
 111 gid_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
 132 static __init int user_namespaces_init(void)
 133 {
 134         user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
 135         return 0;
 136 }
 137 module_init(user_namespaces_init);