5 files changed, 644 insertions, 48 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 1c8b280146d7..2ee514c7e64a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -81,6 +81,7 @@
 #include <linux/oom.h>
 #include <linux/elf.h>
 #include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
 #include <linux/fs_struct.h>
 #include <linux/slab.h>
 #include <linux/flex_array.h>
@@ -2943,6 +2944,74 @@ static int proc_tgid_io_accounting(struct task_struct *task, char *buffer)
 }
 #endif /* CONFIG_TASK_IO_ACCOUNTING */
 
+#ifdef CONFIG_USER_NS
+static int proc_id_map_open(struct inode *inode, struct file *file,
+	struct seq_operations *seq_ops)
+{
+	struct user_namespace *ns = NULL;
+	struct task_struct *task;
+	struct seq_file *seq;
+	int ret = -EINVAL;
+
+	task = get_proc_task(inode);
+	if (task) {
+		rcu_read_lock();
+		ns = get_user_ns(task_cred_xxx(task, user_ns));
+		rcu_read_unlock();
+		put_task_struct(task);
+	}
+	if (!ns)
+		goto err;
+
+	ret = seq_open(file, seq_ops);
+	if (ret)
+		goto err_put_ns;
+
+	seq = file->private_data;
+	seq->private = ns;
+
+	return 0;
+err_put_ns:
+	put_user_ns(ns);
+err:
+	return ret;
+}
+
+static int proc_id_map_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+	struct user_namespace *ns = seq->private;
+	put_user_ns(ns);
+	return seq_release(inode, file);
+}
+
+static int proc_uid_map_open(struct inode *inode, struct file *file)
+{
+	return proc_id_map_open(inode, file, &proc_uid_seq_operations);
+}
+
+static int proc_gid_map_open(struct inode *inode, struct file *file)
+{
+	return proc_id_map_open(inode, file, &proc_gid_seq_operations);
+}
+
+static const struct file_operations proc_uid_map_operations = {
+	.open		= proc_uid_map_open,
+	.write		= proc_uid_map_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= proc_id_map_release,
+};
+
+static const struct file_operations proc_gid_map_operations = {
+	.open		= proc_gid_map_open,
+	.write		= proc_gid_map_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= proc_id_map_release,
+};
+#endif /* CONFIG_USER_NS */
+
 static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
 				struct pid *pid, struct task_struct *task)
 {
@@ -3045,6 +3114,10 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_HARDWALL
 	INF("hardwall",   S_IRUGO, proc_pid_hardwall),
 #endif
+#ifdef CONFIG_USER_NS
+	REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
+	REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
+#endif
 };
 
 static int proc_tgid_base_readdir(struct file * filp,
@@ -3400,6 +3473,10 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_HARDWALL
 	INF("hardwall",   S_IRUGO, proc_pid_hardwall),
 #endif
+#ifdef CONFIG_USER_NS
+	REG("uid_map",    S_IRUGO|S_IWUSR, proc_uid_map_operations),
+	REG("gid_map",    S_IRUGO|S_IWUSR, proc_gid_map_operations),
+#endif
 };
 
 static int proc_tid_base_readdir(struct file * filp,
diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
index 539856829caf..8e522cbcef29 100644
--- a/include/linux/uidgid.h
+++ b/include/linux/uidgid.h
@@ -127,6 +127,28 @@ static inline bool gid_valid(kgid_t gid)
 	return !gid_eq(gid, INVALID_GID);
 }
 
+#ifdef CONFIG_USER_NS
+
+extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);
+extern kgid_t make_kgid(struct user_namespace *from, gid_t gid);
+
+extern uid_t from_kuid(struct user_namespace *to, kuid_t uid);
+extern gid_t from_kgid(struct user_namespace *to, kgid_t gid);
+extern uid_t from_kuid_munged(struct user_namespace *to, kuid_t uid);
+extern gid_t from_kgid_munged(struct user_namespace *to, kgid_t gid);
+
+static inline bool kuid_has_mapping(struct user_namespace *ns, kuid_t uid)
+{
+	return from_kuid(ns, uid) != (uid_t) -1;
+}
+
+static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
+{
+	return from_kgid(ns, gid) != (gid_t) -1;
+}
+
+#else
+
 static inline kuid_t make_kuid(struct user_namespace *from, uid_t uid)
 {
 	return KUIDT_INIT(uid);
@@ -173,4 +195,6 @@ static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
 	return true;
 }
 
+#endif /* CONFIG_USER_NS */
+
 #endif /* _LINUX_UIDGID_H */
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 8a391bd53de2..4c9846d90741 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -6,7 +6,20 @@
 #include <linux/sched.h>
 #include <linux/err.h>
 
+#define UID_GID_MAP_MAX_EXTENTS 5
+
+struct uid_gid_map {	/* 64 bytes -- 1 cache line */
+	u32 nr_extents;
+	struct uid_gid_extent {
+		u32 first;
+		u32 lower_first;
+		u32 count;
+	} extent[UID_GID_MAP_MAX_EXTENTS];
+};
+
 struct user_namespace {
+	struct uid_gid_map	uid_map;
+	struct uid_gid_map	gid_map;
 	struct kref		kref;
 	struct user_namespace	*parent;
 	kuid_t			owner;
@@ -33,9 +46,11 @@ static inline void put_user_ns(struct user_namespace *ns)
 		kref_put(&ns->kref, free_user_ns);
 }
 
-uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid);
-gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid);
-
+struct seq_operations;
+extern struct seq_operations proc_uid_seq_operations;
+extern struct seq_operations proc_gid_seq_operations;
+extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
+extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
 #else
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -52,17 +67,18 @@ static inline void put_user_ns(struct user_namespace *ns)
 {
 }
 
+#endif
+
 static inline uid_t user_ns_map_uid(struct user_namespace *to,
 	const struct cred *cred, uid_t uid)
 {
-	return uid;
+	return from_kuid_munged(to, make_kuid(cred->user_ns, uid));
 }
+
 static inline gid_t user_ns_map_gid(struct user_namespace *to,
 	const struct cred *cred, gid_t gid)
 {
-	return gid;
+	return from_kgid_munged(to, make_kgid(cred->user_ns, gid));
 }
 
-#endif
-
 #endif /* _LINUX_USER_H */
diff --git a/kernel/user.c b/kernel/user.c
index cff385659175..f9e420e36699 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -22,6 +22,22 @@
  * and 1 for... ?
  */
 struct user_namespace init_user_ns = {
+	.uid_map = {
+		.nr_extents = 1,
+		.extent[0] = {
+			.first = 0,
+			.lower_first = 0,
+			.count = 4294967295,
+		},
+	},
+	.gid_map = {
+		.nr_extents = 1,
+		.extent[0] = {
+			.first = 0,
+			.lower_first = 0,
+			.count = 4294967295,
+		},
+	},
 	.kref = {
 		.refcount	= ATOMIC_INIT(3),
 	},
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index ed08836558e0..7eff867bfac5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -12,9 +12,19 @@
 #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>
 
 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);
+
 /*
  * 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
@@ -26,7 +36,6 @@ static struct kmem_cache *user_ns_cachep __read_mostly;
 int create_user_ns(struct cred *new)
 {
 	struct user_namespace *ns, *parent_ns = new->user_ns;
-	struct user_struct *root_user;
 	kuid_t owner = make_kuid(new->user_ns, new->euid);
 	kgid_t group = make_kgid(new->user_ns, new->egid);
 
@@ -38,29 +47,15 @@ int create_user_ns(struct cred *new)
 	    !kgid_has_mapping(parent_ns, group))
 		return -EPERM;
 
-	ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);
+	ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
 	if (!ns)
 		return -ENOMEM;
 
 	kref_init(&ns->kref);
-
-	/* Alloc new root user.  */
-	root_user = alloc_uid(make_kuid(ns, 0));
-	if (!root_user) {
-		kmem_cache_free(user_ns_cachep, ns);
-		return -ENOMEM;
-	}
-
-	/* set the new root user in the credentials under preparation */
 	ns->parent = parent_ns;
 	ns->owner = owner;
 	ns->group = group;
-	free_uid(new->user);
-	new->user = root_user;
-	new->uid = new->euid = new->suid = new->fsuid = 0;
-	new->gid = new->egid = new->sgid = new->fsgid = 0;
-	put_group_info(new->group_info);
-	new->group_info = get_group_info(&init_groups);
+
 	/* Start with the same capabilities as init but useless for doing
 	 * anything as the capabilities are bound to the new user namespace.
 	 */
@@ -93,44 +88,512 @@ void free_user_ns(struct kref *kref)
 }
 EXPORT_SYMBOL(free_user_ns);
 
-uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
+static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
 {
-	struct user_namespace *tmp;
+	unsigned idx, extents;
+	u32 first, last, id2;
 
-	if (likely(to == cred->user_ns))
-		return uid;
+	id2 = id + count - 1;
 
-	/* Is cred->user the creator of the target user_ns
-	 * or the creator of one of it's parents?
-	 */
-	for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
-		if (uid_eq(cred->user->uid, tmp->owner)) {
-			return (uid_t)0;
-		}
+	/* 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);
+
+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;
 
-	/* No useful relationship so no mapping */
-	return overflowuid;
+	lower_ns = current_user_ns();
+	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;
 }
 
-gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
+static int gid_m_show(struct seq_file *seq, void *v)
 {
-	struct user_namespace *tmp;
+	struct user_namespace *ns = seq->private;
+	struct uid_gid_extent *extent = v;
+	struct user_namespace *lower_ns;
+	gid_t lower;
 
-	if (likely(to == cred->user_ns))
-		return gid;
+	lower_ns = current_user_ns();
+	if ((lower_ns == ns) && lower_ns->parent)
+		lower_ns = lower_ns->parent;
 
-	/* Is cred->user the creator of the target user_ns
-	 * or the creator of one of it's parents?
+	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 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 *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,
+};
+
+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.
 	 */
-	for ( tmp = to; tmp != &init_user_ns; tmp = tmp->parent ) {
-		if (uid_eq(cred->user->uid, tmp->owner)) {
-			return (gid_t)0;
+	if (!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;
+
+	if (!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;
+
+	if (!ns->parent)
+		return -EPERM;
+
+	return map_write(file, buf, size, ppos, CAP_SETGID,
+			 &ns->gid_map, &ns->parent->gid_map);
+}
+
+static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
+				struct uid_gid_map *new_map)
+{
+	/* 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;
 
-	/* No useful relationship so no mapping */
-	return overflowgid;
+	return false;
 }
 
 static __init int user_namespaces_init(void)