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 #include <linux/securebits.h>
  15
  16 static struct kmem_cache *user_ns_cachep __read_mostly;
  17
  18 /*
  19  * Create a new user namespace, deriving the creator from the user in the
  20  * passed credentials, and replacing that user with the new root user for the
  21  * new namespace.
  22  *
  23  * This is called by copy_creds(), which will finish setting the target task's
  24  * credentials.
  25  */
  26 int create_user_ns(struct cred *new)
  27 {
  28         struct user_namespace *ns, *parent_ns = new->user_ns;
  29         struct user_struct *root_user;
  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         /* Alloc new root user.  */
  38         root_user = alloc_uid(make_kuid(ns, 0));
  39         if (!root_user) {
  40                 kmem_cache_free(user_ns_cachep, ns);
  41                 return -ENOMEM;
  42         }
  43
  44         /* set the new root user in the credentials under preparation */
  45         ns->parent = parent_ns;
  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         /* Start with the same capabilities as init but useless for doing
  53          * anything as the capabilities are bound to the new user namespace.
  54          */
  55         new->securebits = SECUREBITS_DEFAULT;
  56         new->cap_inheritable = CAP_EMPTY_SET;
  57         new->cap_permitted = CAP_FULL_SET;
  58         new->cap_effective = CAP_FULL_SET;
  59         new->cap_bset = CAP_FULL_SET;
  60 #ifdef CONFIG_KEYS
  61         key_put(new->request_key_auth);
  62         new->request_key_auth = NULL;
  63 #endif
  64         /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
  65
  66         /* Leave the reference to our user_ns with the new cred */
  67         new->user_ns = ns;
  68
  69         return 0;
  70 }
  71
  72 /*
  73  * Deferred destructor for a user namespace.  This is required because
  74  * free_user_ns() may be called with uidhash_lock held, but we need to call
  75  * back to free_uid() which will want to take the lock again.
  76  */
  77 static void free_user_ns_work(struct work_struct *work)
  78 {
  79         struct user_namespace *parent, *ns =
  80                 container_of(work, struct user_namespace, destroyer);
  81         parent = ns->parent;
  82         free_uid(ns->creator);
  83         kmem_cache_free(user_ns_cachep, ns);
  84         put_user_ns(parent);
  85 }
  86
  87 void free_user_ns(struct kref *kref)
  88 {
  89         struct user_namespace *ns =
  90                 container_of(kref, struct user_namespace, kref);
  91
  92         INIT_WORK(&ns->destroyer, free_user_ns_work);
  93         schedule_work(&ns->destroyer);
  94 }
  95 EXPORT_SYMBOL(free_user_ns);
  96
  97 uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
  98 {
  99         struct user_namespace *tmp;
 100
 101         if (likely(to == cred->user_ns))
 102                 return uid;
 103
 104
 105         /* Is cred->user the creator of the target user_ns
 106          * or the creator of one of it's parents?
 107          */
 108         for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
 109                 if (cred->user == tmp->creator) {
 110                         return (uid_t)0;
 111                 }
 112         }
 113
 114         /* No useful relationship so no mapping */
 115         return overflowuid;
 116 }
 117
 118 gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
 119 {
 120         struct user_namespace *tmp;
 121
 122         if (likely(to == cred->user_ns))
 123                 return gid;
 124
 125         /* Is cred->user the creator of the target user_ns
 126          * or the creator of one of it's parents?
 127          */
 128         for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
 129                 if (cred->user == tmp->creator) {
 130                         return (gid_t)0;
 131                 }
 132         }
 133
 134         /* No useful relationship so no mapping */
 135         return overflowgid;
 136 }
 137
 138 static __init int user_namespaces_init(void)
 139 {
 140         user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
 141         return 0;
 142 }
 143 module_init(user_namespaces_init);