FreeBSD/Linux Kernel Cross Reference
sys/kernel/user_namespace.c

     /*
      *  This program is free software; you can redistribute it and/or
      *  modify it under the terms of the GNU General Public License as
      *  published by the Free Software Foundation, version 2 of the
      *  License.
      */
     
     #include <linux/export.h>
     #include <linux/nsproxy.h>
    #include <linux/slab.h>
    #include <linux/user_namespace.h>
    #include <linux/proc_fs.h>
    #include <linux/highuid.h>
    #include <linux/cred.h>
    #include <linux/securebits.h>
    #include <linux/keyctl.h>
    #include <linux/key-type.h>
    #include <keys/user-type.h>
    #include <linux/seq_file.h>
    #include <linux/fs.h>
    #include <linux/uaccess.h>
    #include <linux/ctype.h>
    #include <linux/projid.h>
    
    static struct kmem_cache *user_ns_cachep __read_mostly;
    
    static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
                                    struct uid_gid_map *map);
    
    static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
    {
            /* Start with the same capabilities as init but useless for doing
             * anything as the capabilities are bound to the new user namespace.
             */
            cred->securebits = SECUREBITS_DEFAULT;
            cred->cap_inheritable = CAP_EMPTY_SET;
            cred->cap_permitted = CAP_FULL_SET;
            cred->cap_effective = CAP_FULL_SET;
            cred->cap_bset = CAP_FULL_SET;
    #ifdef CONFIG_KEYS
            key_put(cred->request_key_auth);
            cred->request_key_auth = NULL;
    #endif
            /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
            cred->user_ns = user_ns;
    }
    
    /*
     * Create a new user namespace, deriving the creator from the user in the
     * passed credentials, and replacing that user with the new root user for the
     * new namespace.
     *
     * This is called by copy_creds(), which will finish setting the target task's
     * credentials.
     */
    int create_user_ns(struct cred *new)
    {
            struct user_namespace *ns, *parent_ns = new->user_ns;
            kuid_t owner = new->euid;
            kgid_t group = new->egid;
            int ret;
    
            /* The creator needs a mapping in the parent user namespace
             * or else we won't be able to reasonably tell userspace who
             * created a user_namespace.
             */
            if (!kuid_has_mapping(parent_ns, owner) ||
                !kgid_has_mapping(parent_ns, group))
                    return -EPERM;
    
            ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
            if (!ns)
                    return -ENOMEM;
    
            ret = proc_alloc_inum(&ns->proc_inum);
            if (ret) {
                    kmem_cache_free(user_ns_cachep, ns);
                    return ret;
            }
    
            kref_init(&ns->kref);
            /* Leave the new->user_ns reference with the new user namespace. */
            ns->parent = parent_ns;
            ns->owner = owner;
            ns->group = group;
    
            set_cred_user_ns(new, ns);
    
            return 0;
    }
    
    int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
    {
            struct cred *cred;
    
            if (!(unshare_flags & CLONE_NEWUSER))
                    return 0;
    
            cred = prepare_creds();
           if (!cred)
                   return -ENOMEM;
   
           *new_cred = cred;
           return create_user_ns(cred);
   }
   
   void free_user_ns(struct kref *kref)
   {
           struct user_namespace *parent, *ns =
                   container_of(kref, struct user_namespace, kref);
   
           parent = ns->parent;
           proc_free_inum(ns->proc_inum);
           kmem_cache_free(user_ns_cachep, ns);
           put_user_ns(parent);
   }
   EXPORT_SYMBOL(free_user_ns);
   
   static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
   {
           unsigned idx, extents;
           u32 first, last, id2;
   
           id2 = id + count - 1;
   
           /* Find the matching extent */
           extents = map->nr_extents;
           smp_read_barrier_depends();
           for (idx = 0; idx < extents; idx++) {
                   first = map->extent[idx].first;
                   last = first + map->extent[idx].count - 1;
                   if (id >= first && id <= last &&
                       (id2 >= first && id2 <= last))
                           break;
           }
           /* Map the id or note failure */
           if (idx < extents)
                   id = (id - first) + map->extent[idx].lower_first;
           else
                   id = (u32) -1;
   
           return id;
   }
   
   static u32 map_id_down(struct uid_gid_map *map, u32 id)
   {
           unsigned idx, extents;
           u32 first, last;
   
           /* Find the matching extent */
           extents = map->nr_extents;
           smp_read_barrier_depends();
           for (idx = 0; idx < extents; idx++) {
                   first = map->extent[idx].first;
                   last = first + map->extent[idx].count - 1;
                   if (id >= first && id <= last)
                           break;
           }
           /* Map the id or note failure */
           if (idx < extents)
                   id = (id - first) + map->extent[idx].lower_first;
           else
                   id = (u32) -1;
   
           return id;
   }
   
   static u32 map_id_up(struct uid_gid_map *map, u32 id)
   {
           unsigned idx, extents;
           u32 first, last;
   
           /* Find the matching extent */
           extents = map->nr_extents;
           smp_read_barrier_depends();
           for (idx = 0; idx < extents; idx++) {
                   first = map->extent[idx].lower_first;
                   last = first + map->extent[idx].count - 1;
                   if (id >= first && id <= last)
                           break;
           }
           /* Map the id or note failure */
           if (idx < extents)
                   id = (id - first) + map->extent[idx].first;
           else
                   id = (u32) -1;
   
           return id;
   }
   
   /**
    *      make_kuid - Map a user-namespace uid pair into a kuid.
    *      @ns:  User namespace that the uid is in
    *      @uid: User identifier
    *
    *      Maps a user-namespace uid pair into a kernel internal kuid,
    *      and returns that kuid.
    *
    *      When there is no mapping defined for the user-namespace uid
    *      pair INVALID_UID is returned.  Callers are expected to test
    *      for and handle handle INVALID_UID being returned.  INVALID_UID
    *      may be tested for using uid_valid().
    */
   kuid_t make_kuid(struct user_namespace *ns, uid_t uid)
   {
           /* Map the uid to a global kernel uid */
           return KUIDT_INIT(map_id_down(&ns->uid_map, uid));
   }
   EXPORT_SYMBOL(make_kuid);
   
   /**
    *      from_kuid - Create a uid from a kuid user-namespace pair.
    *      @targ: The user namespace we want a uid in.
    *      @kuid: The kernel internal uid to start with.
    *
    *      Map @kuid into the user-namespace specified by @targ and
    *      return the resulting uid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      If @kuid has no mapping in @targ (uid_t)-1 is returned.
    */
   uid_t from_kuid(struct user_namespace *targ, kuid_t kuid)
   {
           /* Map the uid from a global kernel uid */
           return map_id_up(&targ->uid_map, __kuid_val(kuid));
   }
   EXPORT_SYMBOL(from_kuid);
   
   /**
    *      from_kuid_munged - Create a uid from a kuid user-namespace pair.
    *      @targ: The user namespace we want a uid in.
    *      @kuid: The kernel internal uid to start with.
    *
    *      Map @kuid into the user-namespace specified by @targ and
    *      return the resulting uid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      Unlike from_kuid from_kuid_munged never fails and always
    *      returns a valid uid.  This makes from_kuid_munged appropriate
    *      for use in syscalls like stat and getuid where failing the
    *      system call and failing to provide a valid uid are not an
    *      options.
    *
    *      If @kuid has no mapping in @targ overflowuid is returned.
    */
   uid_t from_kuid_munged(struct user_namespace *targ, kuid_t kuid)
   {
           uid_t uid;
           uid = from_kuid(targ, kuid);
   
           if (uid == (uid_t) -1)
                   uid = overflowuid;
           return uid;
   }
   EXPORT_SYMBOL(from_kuid_munged);
   
   /**
    *      make_kgid - Map a user-namespace gid pair into a kgid.
    *      @ns:  User namespace that the gid is in
    *      @uid: group identifier
    *
    *      Maps a user-namespace gid pair into a kernel internal kgid,
    *      and returns that kgid.
    *
    *      When there is no mapping defined for the user-namespace gid
    *      pair INVALID_GID is returned.  Callers are expected to test
    *      for and handle INVALID_GID being returned.  INVALID_GID may be
    *      tested for using gid_valid().
    */
   kgid_t make_kgid(struct user_namespace *ns, gid_t gid)
   {
           /* Map the gid to a global kernel gid */
           return KGIDT_INIT(map_id_down(&ns->gid_map, gid));
   }
   EXPORT_SYMBOL(make_kgid);
   
   /**
    *      from_kgid - Create a gid from a kgid user-namespace pair.
    *      @targ: The user namespace we want a gid in.
    *      @kgid: The kernel internal gid to start with.
    *
    *      Map @kgid into the user-namespace specified by @targ and
    *      return the resulting gid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      If @kgid has no mapping in @targ (gid_t)-1 is returned.
    */
   gid_t from_kgid(struct user_namespace *targ, kgid_t kgid)
   {
           /* Map the gid from a global kernel gid */
           return map_id_up(&targ->gid_map, __kgid_val(kgid));
   }
   EXPORT_SYMBOL(from_kgid);
   
   /**
    *      from_kgid_munged - Create a gid from a kgid user-namespace pair.
    *      @targ: The user namespace we want a gid in.
    *      @kgid: The kernel internal gid to start with.
    *
    *      Map @kgid into the user-namespace specified by @targ and
    *      return the resulting gid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      Unlike from_kgid from_kgid_munged never fails and always
    *      returns a valid gid.  This makes from_kgid_munged appropriate
    *      for use in syscalls like stat and getgid where failing the
    *      system call and failing to provide a valid gid are not options.
    *
    *      If @kgid has no mapping in @targ overflowgid is returned.
    */
   gid_t from_kgid_munged(struct user_namespace *targ, kgid_t kgid)
   {
           gid_t gid;
           gid = from_kgid(targ, kgid);
   
           if (gid == (gid_t) -1)
                   gid = overflowgid;
           return gid;
   }
   EXPORT_SYMBOL(from_kgid_munged);
   
   /**
    *      make_kprojid - Map a user-namespace projid pair into a kprojid.
    *      @ns:  User namespace that the projid is in
    *      @projid: Project identifier
    *
    *      Maps a user-namespace uid pair into a kernel internal kuid,
    *      and returns that kuid.
    *
    *      When there is no mapping defined for the user-namespace projid
    *      pair INVALID_PROJID is returned.  Callers are expected to test
    *      for and handle handle INVALID_PROJID being returned.  INVALID_PROJID
    *      may be tested for using projid_valid().
    */
   kprojid_t make_kprojid(struct user_namespace *ns, projid_t projid)
   {
           /* Map the uid to a global kernel uid */
           return KPROJIDT_INIT(map_id_down(&ns->projid_map, projid));
   }
   EXPORT_SYMBOL(make_kprojid);
   
   /**
    *      from_kprojid - Create a projid from a kprojid user-namespace pair.
    *      @targ: The user namespace we want a projid in.
    *      @kprojid: The kernel internal project identifier to start with.
    *
    *      Map @kprojid into the user-namespace specified by @targ and
    *      return the resulting projid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      If @kprojid has no mapping in @targ (projid_t)-1 is returned.
    */
   projid_t from_kprojid(struct user_namespace *targ, kprojid_t kprojid)
   {
           /* Map the uid from a global kernel uid */
           return map_id_up(&targ->projid_map, __kprojid_val(kprojid));
   }
   EXPORT_SYMBOL(from_kprojid);
   
   /**
    *      from_kprojid_munged - Create a projiid from a kprojid user-namespace pair.
    *      @targ: The user namespace we want a projid in.
    *      @kprojid: The kernel internal projid to start with.
    *
    *      Map @kprojid into the user-namespace specified by @targ and
    *      return the resulting projid.
    *
    *      There is always a mapping into the initial user_namespace.
    *
    *      Unlike from_kprojid from_kprojid_munged never fails and always
    *      returns a valid projid.  This makes from_kprojid_munged
    *      appropriate for use in syscalls like stat and where
    *      failing the system call and failing to provide a valid projid are
    *      not an options.
    *
    *      If @kprojid has no mapping in @targ OVERFLOW_PROJID is returned.
    */
   projid_t from_kprojid_munged(struct user_namespace *targ, kprojid_t kprojid)
   {
           projid_t projid;
           projid = from_kprojid(targ, kprojid);
   
           if (projid == (projid_t) -1)
                   projid = OVERFLOW_PROJID;
           return projid;
   }
   EXPORT_SYMBOL(from_kprojid_munged);
   
   
   static int uid_m_show(struct seq_file *seq, void *v)
   {
           struct user_namespace *ns = seq->private;
           struct uid_gid_extent *extent = v;
           struct user_namespace *lower_ns;
           uid_t lower;
   
           lower_ns = seq_user_ns(seq);
           if ((lower_ns == ns) && lower_ns->parent)
                   lower_ns = lower_ns->parent;
   
           lower = from_kuid(lower_ns, KUIDT_INIT(extent->lower_first));
   
           seq_printf(seq, "%10u %10u %10u\n",
                   extent->first,
                   lower,
                   extent->count);
   
           return 0;
   }
   
   static int gid_m_show(struct seq_file *seq, void *v)
   {
           struct user_namespace *ns = seq->private;
           struct uid_gid_extent *extent = v;
           struct user_namespace *lower_ns;
           gid_t lower;
   
           lower_ns = seq_user_ns(seq);
           if ((lower_ns == ns) && lower_ns->parent)
                   lower_ns = lower_ns->parent;
   
           lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));
   
           seq_printf(seq, "%10u %10u %10u\n",
                   extent->first,
                   lower,
                   extent->count);
   
           return 0;
   }
   
   static int projid_m_show(struct seq_file *seq, void *v)
   {
           struct user_namespace *ns = seq->private;
           struct uid_gid_extent *extent = v;
           struct user_namespace *lower_ns;
           projid_t lower;
   
           lower_ns = seq_user_ns(seq);
           if ((lower_ns == ns) && lower_ns->parent)
                   lower_ns = lower_ns->parent;
   
           lower = from_kprojid(lower_ns, KPROJIDT_INIT(extent->lower_first));
   
           seq_printf(seq, "%10u %10u %10u\n",
                   extent->first,
                   lower,
                   extent->count);
   
           return 0;
   }
   
   static void *m_start(struct seq_file *seq, loff_t *ppos, struct uid_gid_map *map)
   {
           struct uid_gid_extent *extent = NULL;
           loff_t pos = *ppos;
   
           if (pos < map->nr_extents)
                   extent = &map->extent[pos];
   
           return extent;
   }
   
   static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
   {
           struct user_namespace *ns = seq->private;
   
           return m_start(seq, ppos, &ns->uid_map);
   }
   
   static void *gid_m_start(struct seq_file *seq, loff_t *ppos)
   {
           struct user_namespace *ns = seq->private;
   
           return m_start(seq, ppos, &ns->gid_map);
   }
   
   static void *projid_m_start(struct seq_file *seq, loff_t *ppos)
   {
           struct user_namespace *ns = seq->private;
   
           return m_start(seq, ppos, &ns->projid_map);
   }
   
   static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
   {
           (*pos)++;
           return seq->op->start(seq, pos);
   }
   
   static void m_stop(struct seq_file *seq, void *v)
   {
           return;
   }
   
   struct seq_operations proc_uid_seq_operations = {
           .start = uid_m_start,
           .stop = m_stop,
           .next = m_next,
           .show = uid_m_show,
   };
   
   struct seq_operations proc_gid_seq_operations = {
           .start = gid_m_start,
           .stop = m_stop,
           .next = m_next,
           .show = gid_m_show,
   };
   
   struct seq_operations proc_projid_seq_operations = {
           .start = projid_m_start,
           .stop = m_stop,
           .next = m_next,
           .show = projid_m_show,
   };
   
   static DEFINE_MUTEX(id_map_mutex);
   
   static ssize_t map_write(struct file *file, const char __user *buf,
                            size_t count, loff_t *ppos,
                            int cap_setid,
                            struct uid_gid_map *map,
                            struct uid_gid_map *parent_map)
   {
           struct seq_file *seq = file->private_data;
           struct user_namespace *ns = seq->private;
           struct uid_gid_map new_map;
           unsigned idx;
           struct uid_gid_extent *extent, *last = NULL;
           unsigned long page = 0;
           char *kbuf, *pos, *next_line;
           ssize_t ret = -EINVAL;
   
           /*
            * The id_map_mutex serializes all writes to any given map.
            *
            * Any map is only ever written once.
            *
            * An id map fits within 1 cache line on most architectures.
            *
            * On read nothing needs to be done unless you are on an
            * architecture with a crazy cache coherency model like alpha.
            *
            * There is a one time data dependency between reading the
            * count of the extents and the values of the extents.  The
            * desired behavior is to see the values of the extents that
            * were written before the count of the extents.
            *
            * To achieve this smp_wmb() is used on guarantee the write
            * order and smp_read_barrier_depends() is guaranteed that we
            * don't have crazy architectures returning stale data.
            *
            */
           mutex_lock(&id_map_mutex);
   
           ret = -EPERM;
           /* Only allow one successful write to the map */
           if (map->nr_extents != 0)
                   goto out;
   
           /* Require the appropriate privilege CAP_SETUID or CAP_SETGID
            * over the user namespace in order to set the id mapping.
            */
           if (cap_valid(cap_setid) && !ns_capable(ns, cap_setid))
                   goto out;
   
           /* Get a buffer */
           ret = -ENOMEM;
           page = __get_free_page(GFP_TEMPORARY);
           kbuf = (char *) page;
           if (!page)
                   goto out;
   
           /* Only allow <= page size writes at the beginning of the file */
           ret = -EINVAL;
           if ((*ppos != 0) || (count >= PAGE_SIZE))
                   goto out;
   
           /* Slurp in the user data */
           ret = -EFAULT;
           if (copy_from_user(kbuf, buf, count))
                   goto out;
           kbuf[count] = '\0';
   
           /* Parse the user data */
           ret = -EINVAL;
           pos = kbuf;
           new_map.nr_extents = 0;
           for (;pos; pos = next_line) {
                   extent = &new_map.extent[new_map.nr_extents];
   
                   /* Find the end of line and ensure I don't look past it */
                   next_line = strchr(pos, '\n');
                   if (next_line) {
                           *next_line = '\0';
                           next_line++;
                           if (*next_line == '\0')
                                   next_line = NULL;
                   }
   
                   pos = skip_spaces(pos);
                   extent->first = simple_strtoul(pos, &pos, 10);
                   if (!isspace(*pos))
                           goto out;
   
                   pos = skip_spaces(pos);
                   extent->lower_first = simple_strtoul(pos, &pos, 10);
                   if (!isspace(*pos))
                           goto out;
   
                   pos = skip_spaces(pos);
                   extent->count = simple_strtoul(pos, &pos, 10);
                   if (*pos && !isspace(*pos))
                           goto out;
   
                   /* Verify there is not trailing junk on the line */
                   pos = skip_spaces(pos);
                   if (*pos != '\0')
                           goto out;
   
                   /* Verify we have been given valid starting values */
                   if ((extent->first == (u32) -1) ||
                       (extent->lower_first == (u32) -1 ))
                           goto out;
   
                   /* Verify count is not zero and does not cause the extent to wrap */
                   if ((extent->first + extent->count) <= extent->first)
                           goto out;
                   if ((extent->lower_first + extent->count) <= extent->lower_first)
                           goto out;
   
                   /* For now only accept extents that are strictly in order */
                   if (last &&
                       (((last->first + last->count) > extent->first) ||
                        ((last->lower_first + last->count) > extent->lower_first)))
                           goto out;
   
                   new_map.nr_extents++;
                   last = extent;
   
                   /* Fail if the file contains too many extents */
                   if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&
                       (next_line != NULL))
                           goto out;
           }
           /* Be very certaint the new map actually exists */
           if (new_map.nr_extents == 0)
                   goto out;
   
           ret = -EPERM;
           /* Validate the user is allowed to use user id's mapped to. */
           if (!new_idmap_permitted(ns, cap_setid, &new_map))
                   goto out;
   
           /* Map the lower ids from the parent user namespace to the
            * kernel global id space.
            */
           for (idx = 0; idx < new_map.nr_extents; idx++) {
                   u32 lower_first;
                   extent = &new_map.extent[idx];
   
                   lower_first = map_id_range_down(parent_map,
                                                   extent->lower_first,
                                                   extent->count);
   
                   /* Fail if we can not map the specified extent to
                    * the kernel global id space.
                    */
                   if (lower_first == (u32) -1)
                           goto out;
   
                   extent->lower_first = lower_first;
           }
   
           /* Install the map */
           memcpy(map->extent, new_map.extent,
                   new_map.nr_extents*sizeof(new_map.extent[0]));
           smp_wmb();
           map->nr_extents = new_map.nr_extents;
   
           *ppos = count;
           ret = count;
   out:
           mutex_unlock(&id_map_mutex);
           if (page)
                   free_page(page);
           return ret;
   }
   
   ssize_t proc_uid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
   {
           struct seq_file *seq = file->private_data;
           struct user_namespace *ns = seq->private;
           struct user_namespace *seq_ns = seq_user_ns(seq);
   
           if (!ns->parent)
                   return -EPERM;
   
           if ((seq_ns != ns) && (seq_ns != ns->parent))
                   return -EPERM;
   
           return map_write(file, buf, size, ppos, CAP_SETUID,
                            &ns->uid_map, &ns->parent->uid_map);
   }
   
   ssize_t proc_gid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
   {
           struct seq_file *seq = file->private_data;
           struct user_namespace *ns = seq->private;
           struct user_namespace *seq_ns = seq_user_ns(seq);
   
           if (!ns->parent)
                   return -EPERM;
   
           if ((seq_ns != ns) && (seq_ns != ns->parent))
                   return -EPERM;
   
           return map_write(file, buf, size, ppos, CAP_SETGID,
                            &ns->gid_map, &ns->parent->gid_map);
   }
   
   ssize_t proc_projid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
   {
           struct seq_file *seq = file->private_data;
           struct user_namespace *ns = seq->private;
           struct user_namespace *seq_ns = seq_user_ns(seq);
   
           if (!ns->parent)
                   return -EPERM;
   
           if ((seq_ns != ns) && (seq_ns != ns->parent))
                   return -EPERM;
   
           /* Anyone can set any valid project id no capability needed */
           return map_write(file, buf, size, ppos, -1,
                            &ns->projid_map, &ns->parent->projid_map);
   }
   
   static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
                                   struct uid_gid_map *new_map)
   {
           /* Allow mapping to your own filesystem ids */
           if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1)) {
                   u32 id = new_map->extent[0].lower_first;
                   if (cap_setid == CAP_SETUID) {
                           kuid_t uid = make_kuid(ns->parent, id);
                           if (uid_eq(uid, current_fsuid()))
                                   return true;
                   }
                   else if (cap_setid == CAP_SETGID) {
                           kgid_t gid = make_kgid(ns->parent, id);
                           if (gid_eq(gid, current_fsgid()))
                                   return true;
                   }
           }
   
           /* Allow anyone to set a mapping that doesn't require privilege */
           if (!cap_valid(cap_setid))
                   return true;
   
           /* Allow the specified ids if we have the appropriate capability
            * (CAP_SETUID or CAP_SETGID) over the parent user namespace.
            */
           if (ns_capable(ns->parent, cap_setid))
                   return true;
   
           return false;
   }
   
   static void *userns_get(struct task_struct *task)
   {
           struct user_namespace *user_ns;
   
           rcu_read_lock();
           user_ns = get_user_ns(__task_cred(task)->user_ns);
           rcu_read_unlock();
   
           return user_ns;
   }
   
   static void userns_put(void *ns)
   {
           put_user_ns(ns);
   }
   
   static int userns_install(struct nsproxy *nsproxy, void *ns)
   {
           struct user_namespace *user_ns = ns;
           struct cred *cred;
   
           /* Don't allow gaining capabilities by reentering
            * the same user namespace.
            */
           if (user_ns == current_user_ns())
                   return -EINVAL;
   
           /* Threaded processes may not enter a different user namespace */
           if (atomic_read(&current->mm->mm_users) > 1)
                   return -EINVAL;
   
           if (!ns_capable(user_ns, CAP_SYS_ADMIN))
                   return -EPERM;
   
           cred = prepare_creds();
           if (!cred)
                   return -ENOMEM;
   
           put_user_ns(cred->user_ns);
           set_cred_user_ns(cred, get_user_ns(user_ns));
   
           return commit_creds(cred);
   }
   
   static unsigned int userns_inum(void *ns)
   {
           struct user_namespace *user_ns = ns;
           return user_ns->proc_inum;
   }
   
   const struct proc_ns_operations userns_operations = {
           .name           = "user",
           .type           = CLONE_NEWUSER,
           .get            = userns_get,
           .put            = userns_put,
           .install        = userns_install,
           .inum           = userns_inum,
   };
   
   static __init int user_namespaces_init(void)
   {
           user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
           return 0;
   }
   module_init(user_namespaces_init);

Cache object: 35108fb844329e24ad16a4e32269c137