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, *parent_ns = new->user_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->parent = parent_ns;
  49         ns->creator = new->user;
  50         new->user = root_user;
  51         new->uid = new->euid = new->suid = new->fsuid = 0;
  52         new->gid = new->egid = new->sgid = new->fsgid = 0;
  53         put_group_info(new->group_info);
  54         new->group_info = get_group_info(&init_groups);
  55 #ifdef CONFIG_KEYS
  56         key_put(new->request_key_auth);
  57         new->request_key_auth = NULL;
  58 #endif
  59         /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
  60
  61         /* Leave the reference to our user_ns with the new cred */
  62         new->user_ns = ns;
  63
  64         return 0;
  65 }
  66
  67 /*
  68  * Deferred destructor for a user namespace.  This is required because
  69  * free_user_ns() may be called with uidhash_lock held, but we need to call
  70  * back to free_uid() which will want to take the lock again.
  71  */
  72 static void free_user_ns_work(struct work_struct *work)
  73 {
  74         struct user_namespace *parent, *ns =
  75                 container_of(work, struct user_namespace, destroyer);
  76         parent = ns->parent;
  77         free_uid(ns->creator);
  78         kmem_cache_free(user_ns_cachep, ns);
  79         put_user_ns(parent);
  80 }
  81
  82 void free_user_ns(struct kref *kref)
  83 {
  84         struct user_namespace *ns =
  85                 container_of(kref, struct user_namespace, kref);
  86
  87         INIT_WORK(&ns->destroyer, free_user_ns_work);
  88         schedule_work(&ns->destroyer);
  89 }
  90 EXPORT_SYMBOL(free_user_ns);
  91
  92 uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
  93 {
  94         struct user_namespace *tmp;
  95
  96         if (likely(to == cred->user_ns))
  97                 return uid;
  98
  99
 100         /* Is cred->user the creator of the target user_ns
 101          * or the creator of one of it's parents?
 102          */
 103         for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
 104                 if (cred->user == tmp->creator) {
 105                         return (uid_t)0;
 106                 }
 107         }
 108
 109         /* No useful relationship so no mapping */
 110         return overflowuid;
 111 }
 112
 113 gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
 114 {
 115         struct user_namespace *tmp;
 116
 117         if (likely(to == cred->user_ns))
 118                 return gid;
 119
 120         /* Is cred->user the creator of the target user_ns
 121          * or the creator of one of it's parents?
 122          */
 123         for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
 124                 if (cred->user == tmp->creator) {
 125                         return (gid_t)0;
 126                 }
 127         }
 128
 129         /* No useful relationship so no mapping */
 130         return overflowgid;
 131 }
 132
 133 static __init int user_namespaces_init(void)
 134 {
 135         user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
 136         return 0;
 137 }
 138 module_init(user_namespaces_init);