Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1331 insertions, 0 deletions

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
new file mode 100644
index 000000000..923414a24
--- /dev/null
+++ b/kernel/user_namespace.c
@@ -0,0 +1,1331 @@
+/*
+ *  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/sched/signal.h>
+#include <linux/user_namespace.h>
+#include <linux/proc_ns.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>
+#include <linux/fs_struct.h>
+#include <linux/bsearch.h>
+#include <linux/sort.h>
+
+static struct kmem_cache *user_ns_cachep __read_mostly;
+static DEFINE_MUTEX(userns_state_mutex);
+
+static bool new_idmap_permitted(const struct file *file,
+				struct user_namespace *ns, int cap_setid,
+				struct uid_gid_map *map);
+static void free_user_ns(struct work_struct *work);
+
+static struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid)
+{
+	return inc_ucount(ns, uid, UCOUNT_USER_NAMESPACES);
+}
+
+static void dec_user_namespaces(struct ucounts *ucounts)
+{
+	return dec_ucount(ucounts, UCOUNT_USER_NAMESPACES);
+}
+
+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_ambient = CAP_EMPTY_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;
+	struct ucounts *ucounts;
+	int ret, i;
+
+	ret = -ENOSPC;
+	if (parent_ns->level > 32)
+		goto fail;
+
+	ucounts = inc_user_namespaces(parent_ns, owner);
+	if (!ucounts)
+		goto fail;
+
+	/*
+	 * Verify that we can not violate the policy of which files
+	 * may be accessed that is specified by the root directory,
+	 * by verifing that the root directory is at the root of the
+	 * mount namespace which allows all files to be accessed.
+	 */
+	ret = -EPERM;
+	if (current_chrooted())
+		goto fail_dec;
+
+	/* 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.
+	 */
+	ret = -EPERM;
+	if (!kuid_has_mapping(parent_ns, owner) ||
+	    !kgid_has_mapping(parent_ns, group))
+		goto fail_dec;
+
+	ret = -ENOMEM;
+	ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
+	if (!ns)
+		goto fail_dec;
+
+	ret = ns_alloc_inum(&ns->ns);
+	if (ret)
+		goto fail_free;
+	ns->ns.ops = &userns_operations;
+
+	atomic_set(&ns->count, 1);
+	/* Leave the new->user_ns reference with the new user namespace. */
+	ns->parent = parent_ns;
+	ns->level = parent_ns->level + 1;
+	ns->owner = owner;
+	ns->group = group;
+	INIT_WORK(&ns->work, free_user_ns);
+	for (i = 0; i < UCOUNT_COUNTS; i++) {
+		ns->ucount_max[i] = INT_MAX;
+	}
+	ns->ucounts = ucounts;
+
+	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
+	mutex_lock(&userns_state_mutex);
+	ns->flags = parent_ns->flags;
+	mutex_unlock(&userns_state_mutex);
+
+#ifdef CONFIG_PERSISTENT_KEYRINGS
+	init_rwsem(&ns->persistent_keyring_register_sem);
+#endif
+	ret = -ENOMEM;
+	if (!setup_userns_sysctls(ns))
+		goto fail_keyring;
+
+	set_cred_user_ns(new, ns);
+	return 0;
+fail_keyring:
+#ifdef CONFIG_PERSISTENT_KEYRINGS
+	key_put(ns->persistent_keyring_register);
+#endif
+	ns_free_inum(&ns->ns);
+fail_free:
+	kmem_cache_free(user_ns_cachep, ns);
+fail_dec:
+	dec_user_namespaces(ucounts);
+fail:
+	return ret;
+}
+
+int unshare_userns(unsigned long unshare_flags, struct cred **new_cred)
+{
+	struct cred *cred;
+	int err = -ENOMEM;
+
+	if (!(unshare_flags & CLONE_NEWUSER))
+		return 0;
+
+	cred = prepare_creds();
+	if (cred) {
+		err = create_user_ns(cred);
+		if (err)
+			put_cred(cred);
+		else
+			*new_cred = cred;
+	}
+
+	return err;
+}
+
+static void free_user_ns(struct work_struct *work)
+{
+	struct user_namespace *parent, *ns =
+		container_of(work, struct user_namespace, work);
+
+	do {
+		struct ucounts *ucounts = ns->ucounts;
+		parent = ns->parent;
+		if (ns->gid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+			kfree(ns->gid_map.forward);
+			kfree(ns->gid_map.reverse);
+		}
+		if (ns->uid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+			kfree(ns->uid_map.forward);
+			kfree(ns->uid_map.reverse);
+		}
+		if (ns->projid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+			kfree(ns->projid_map.forward);
+			kfree(ns->projid_map.reverse);
+		}
+		retire_userns_sysctls(ns);
+#ifdef CONFIG_PERSISTENT_KEYRINGS
+		key_put(ns->persistent_keyring_register);
+#endif
+		ns_free_inum(&ns->ns);
+		kmem_cache_free(user_ns_cachep, ns);
+		dec_user_namespaces(ucounts);
+		ns = parent;
+	} while (atomic_dec_and_test(&parent->count));
+}
+
+void __put_user_ns(struct user_namespace *ns)
+{
+	schedule_work(&ns->work);
+}
+EXPORT_SYMBOL(__put_user_ns);
+
+/**
+ * idmap_key struct holds the information necessary to find an idmapping in a
+ * sorted idmap array. It is passed to cmp_map_id() as first argument.
+ */
+struct idmap_key {
+	bool map_up; /* true  -> id from kid; false -> kid from id */
+	u32 id; /* id to find */
+	u32 count; /* == 0 unless used with map_id_range_down() */
+};
+
+/**
+ * cmp_map_id - Function to be passed to bsearch() to find the requested
+ * idmapping. Expects struct idmap_key to be passed via @k.
+ */
+static int cmp_map_id(const void *k, const void *e)
+{
+	u32 first, last, id2;
+	const struct idmap_key *key = k;
+	const struct uid_gid_extent *el = e;
+
+	id2 = key->id + key->count - 1;
+
+	/* handle map_id_{down,up}() */
+	if (key->map_up)
+		first = el->lower_first;
+	else
+		first = el->first;
+
+	last = first + el->count - 1;
+
+	if (key->id >= first && key->id <= last &&
+	    (id2 >= first && id2 <= last))
+		return 0;
+
+	if (key->id < first || id2 < first)
+		return -1;
+
+	return 1;
+}
+
+/**
+ * map_id_range_down_max - Find idmap via binary search in ordered idmap array.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static struct uid_gid_extent *
+map_id_range_down_max(unsigned extents, struct uid_gid_map *map, u32 id, u32 count)
+{
+	struct idmap_key key;
+
+	key.map_up = false;
+	key.count = count;
+	key.id = id;
+
+	return bsearch(&key, map->forward, extents,
+		       sizeof(struct uid_gid_extent), cmp_map_id);
+}
+
+/**
+ * map_id_range_down_base - Find idmap via binary search in static extent array.
+ * Can only be called if number of mappings is equal or less than
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static struct uid_gid_extent *
+map_id_range_down_base(unsigned extents, struct uid_gid_map *map, u32 id, u32 count)
+{
+	unsigned idx;
+	u32 first, last, id2;
+
+	id2 = id + count - 1;
+
+	/* Find the matching extent */
+	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))
+			return &map->extent[idx];
+	}
+	return NULL;
+}
+
+static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
+{
+	struct uid_gid_extent *extent;
+	unsigned extents = map->nr_extents;
+	smp_rmb();
+
+	if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+		extent = map_id_range_down_base(extents, map, id, count);
+	else
+		extent = map_id_range_down_max(extents, map, id, count);
+
+	/* Map the id or note failure */
+	if (extent)
+		id = (id - extent->first) + extent->lower_first;
+	else
+		id = (u32) -1;
+
+	return id;
+}
+
+static u32 map_id_down(struct uid_gid_map *map, u32 id)
+{
+	return map_id_range_down(map, id, 1);
+}
+
+/**
+ * map_id_up_base - Find idmap via binary search in static extent array.
+ * Can only be called if number of mappings is equal or less than
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static struct uid_gid_extent *
+map_id_up_base(unsigned extents, struct uid_gid_map *map, u32 id)
+{
+	unsigned idx;
+	u32 first, last;
+
+	/* Find the matching extent */
+	for (idx = 0; idx < extents; idx++) {
+		first = map->extent[idx].lower_first;
+		last = first + map->extent[idx].count - 1;
+		if (id >= first && id <= last)
+			return &map->extent[idx];
+	}
+	return NULL;
+}
+
+/**
+ * map_id_up_max - Find idmap via binary search in ordered idmap array.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static struct uid_gid_extent *
+map_id_up_max(unsigned extents, struct uid_gid_map *map, u32 id)
+{
+	struct idmap_key key;
+
+	key.map_up = true;
+	key.count = 1;
+	key.id = id;
+
+	return bsearch(&key, map->reverse, extents,
+		       sizeof(struct uid_gid_extent), cmp_map_id);
+}
+
+static u32 map_id_up(struct uid_gid_map *map, u32 id)
+{
+	struct uid_gid_extent *extent;
+	unsigned extents = map->nr_extents;
+	smp_rmb();
+
+	if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+		extent = map_id_up_base(extents, map, id);
+	else
+		extent = map_id_up_max(extents, map, id);
+
+	/* Map the id or note failure */
+	if (extent)
+		id = (id - extent->lower_first) + extent->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 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
+ *	@gid: 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)
+{
+	loff_t pos = *ppos;
+	unsigned extents = map->nr_extents;
+	smp_rmb();
+
+	if (pos >= extents)
+		return NULL;
+
+	if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+		return &map->extent[pos];
+
+	return &map->forward[pos];
+}
+
+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;
+}
+
+const struct seq_operations proc_uid_seq_operations = {
+	.start = uid_m_start,
+	.stop = m_stop,
+	.next = m_next,
+	.show = uid_m_show,
+};
+
+const struct seq_operations proc_gid_seq_operations = {
+	.start = gid_m_start,
+	.stop = m_stop,
+	.next = m_next,
+	.show = gid_m_show,
+};
+
+const struct seq_operations proc_projid_seq_operations = {
+	.start = projid_m_start,
+	.stop = m_stop,
+	.next = m_next,
+	.show = projid_m_show,
+};
+
+static bool mappings_overlap(struct uid_gid_map *new_map,
+			     struct uid_gid_extent *extent)
+{
+	u32 upper_first, lower_first, upper_last, lower_last;
+	unsigned idx;
+
+	upper_first = extent->first;
+	lower_first = extent->lower_first;
+	upper_last = upper_first + extent->count - 1;
+	lower_last = lower_first + extent->count - 1;
+
+	for (idx = 0; idx < new_map->nr_extents; idx++) {
+		u32 prev_upper_first, prev_lower_first;
+		u32 prev_upper_last, prev_lower_last;
+		struct uid_gid_extent *prev;
+
+		if (new_map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+			prev = &new_map->extent[idx];
+		else
+			prev = &new_map->forward[idx];
+
+		prev_upper_first = prev->first;
+		prev_lower_first = prev->lower_first;
+		prev_upper_last = prev_upper_first + prev->count - 1;
+		prev_lower_last = prev_lower_first + prev->count - 1;
+
+		/* Does the upper range intersect a previous extent? */
+		if ((prev_upper_first <= upper_last) &&
+		    (prev_upper_last >= upper_first))
+			return true;
+
+		/* Does the lower range intersect a previous extent? */
+		if ((prev_lower_first <= lower_last) &&
+		    (prev_lower_last >= lower_first))
+			return true;
+	}
+	return false;
+}
+
+/**
+ * insert_extent - Safely insert a new idmap extent into struct uid_gid_map.
+ * Takes care to allocate a 4K block of memory if the number of mappings exceeds
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static int insert_extent(struct uid_gid_map *map, struct uid_gid_extent *extent)
+{
+	struct uid_gid_extent *dest;
+
+	if (map->nr_extents == UID_GID_MAP_MAX_BASE_EXTENTS) {
+		struct uid_gid_extent *forward;
+
+		/* Allocate memory for 340 mappings. */
+		forward = kmalloc_array(UID_GID_MAP_MAX_EXTENTS,
+					sizeof(struct uid_gid_extent),
+					GFP_KERNEL);
+		if (!forward)
+			return -ENOMEM;
+
+		/* Copy over memory. Only set up memory for the forward pointer.
+		 * Defer the memory setup for the reverse pointer.
+		 */
+		memcpy(forward, map->extent,
+		       map->nr_extents * sizeof(map->extent[0]));
+
+		map->forward = forward;
+		map->reverse = NULL;
+	}
+
+	if (map->nr_extents < UID_GID_MAP_MAX_BASE_EXTENTS)
+		dest = &map->extent[map->nr_extents];
+	else
+		dest = &map->forward[map->nr_extents];
+
+	*dest = *extent;
+	map->nr_extents++;
+	return 0;
+}
+
+/* cmp function to sort() forward mappings */
+static int cmp_extents_forward(const void *a, const void *b)
+{
+	const struct uid_gid_extent *e1 = a;
+	const struct uid_gid_extent *e2 = b;
+
+	if (e1->first < e2->first)
+		return -1;
+
+	if (e1->first > e2->first)
+		return 1;
+
+	return 0;
+}
+
+/* cmp function to sort() reverse mappings */
+static int cmp_extents_reverse(const void *a, const void *b)
+{
+	const struct uid_gid_extent *e1 = a;
+	const struct uid_gid_extent *e2 = b;
+
+	if (e1->lower_first < e2->lower_first)
+		return -1;
+
+	if (e1->lower_first > e2->lower_first)
+		return 1;
+
+	return 0;
+}
+
+/**
+ * sort_idmaps - Sorts an array of idmap entries.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static int sort_idmaps(struct uid_gid_map *map)
+{
+	if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+		return 0;
+
+	/* Sort forward array. */
+	sort(map->forward, map->nr_extents, sizeof(struct uid_gid_extent),
+	     cmp_extents_forward, NULL);
+
+	/* Only copy the memory from forward we actually need. */
+	map->reverse = kmemdup(map->forward,
+			       map->nr_extents * sizeof(struct uid_gid_extent),
+			       GFP_KERNEL);
+	if (!map->reverse)
+		return -ENOMEM;
+
+	/* Sort reverse array. */
+	sort(map->reverse, map->nr_extents, sizeof(struct uid_gid_extent),
+	     cmp_extents_reverse, NULL);
+
+	return 0;
+}
+
+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;
+	char *kbuf = NULL, *pos, *next_line;
+	ssize_t ret;
+
+	/* Only allow < page size writes at the beginning of the file */
+	if ((*ppos != 0) || (count >= PAGE_SIZE))
+		return -EINVAL;
+
+	/* Slurp in the user data */
+	kbuf = memdup_user_nul(buf, count);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
+
+	/*
+	 * The userns_state_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_rmb() is guaranteed that we don't have crazy
+	 * architectures returning stale data.
+	 */
+	mutex_lock(&userns_state_mutex);
+
+	memset(&new_map, 0, sizeof(struct uid_gid_map));
+
+	ret = -EPERM;
+	/* Only allow one successful write to the map */
+	if (map->nr_extents != 0)
+		goto out;
+
+	/*
+	 * Adjusting namespace settings requires capabilities on the target.
+	 */
+	if (cap_valid(cap_setid) && !file_ns_capable(file, ns, CAP_SYS_ADMIN))
+		goto out;
+
+	/* Parse the user data */
+	ret = -EINVAL;
+	pos = kbuf;
+	for (; pos; pos = next_line) {
+
+		/* 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;
+
+		/* Do the ranges in extent overlap any previous extents? */
+		if (mappings_overlap(&new_map, &extent))
+			goto out;
+
+		if ((new_map.nr_extents + 1) == UID_GID_MAP_MAX_EXTENTS &&
+		    (next_line != NULL))
+			goto out;
+
+		ret = insert_extent(&new_map, &extent);
+		if (ret < 0)
+			goto out;
+		ret = -EINVAL;
+	}
+	/* 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(file, ns, cap_setid, &new_map))
+		goto out;
+
+	ret = -EPERM;
+	/* Map the lower ids from the parent user namespace to the
+	 * kernel global id space.
+	 */
+	for (idx = 0; idx < new_map.nr_extents; idx++) {
+		struct uid_gid_extent *e;
+		u32 lower_first;
+
+		if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+			e = &new_map.extent[idx];
+		else
+			e = &new_map.forward[idx];
+
+		lower_first = map_id_range_down(parent_map,
+						e->lower_first,
+						e->count);
+
+		/* Fail if we can not map the specified extent to
+		 * the kernel global id space.
+		 */
+		if (lower_first == (u32) -1)
+			goto out;
+
+		e->lower_first = lower_first;
+	}
+
+	/*
+	 * If we want to use binary search for lookup, this clones the extent
+	 * array and sorts both copies.
+	 */
+	ret = sort_idmaps(&new_map);
+	if (ret < 0)
+		goto out;
+
+	/* Install the map */
+	if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
+		memcpy(map->extent, new_map.extent,
+		       new_map.nr_extents * sizeof(new_map.extent[0]));
+	} else {
+		map->forward = new_map.forward;
+		map->reverse = new_map.reverse;
+	}
+	smp_wmb();
+	map->nr_extents = new_map.nr_extents;
+
+	*ppos = count;
+	ret = count;
+out:
+	if (ret < 0 && new_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+		kfree(new_map.forward);
+		kfree(new_map.reverse);
+		map->forward = NULL;
+		map->reverse = NULL;
+		map->nr_extents = 0;
+	}
+
+	mutex_unlock(&userns_state_mutex);
+	kfree(kbuf);
+	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(const struct file *file,
+				struct user_namespace *ns, int cap_setid,
+				struct uid_gid_map *new_map)
+{
+	const struct cred *cred = file->f_cred;
+	/* Don't allow mappings that would allow anything that wouldn't
+	 * be allowed without the establishment of unprivileged mappings.
+	 */
+	if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1) &&
+	    uid_eq(ns->owner, cred->euid)) {
+		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, cred->euid))
+				return true;
+		} else if (cap_setid == CAP_SETGID) {
+			kgid_t gid = make_kgid(ns->parent, id);
+			if (!(ns->flags & USERNS_SETGROUPS_ALLOWED) &&
+			    gid_eq(gid, cred->egid))
+				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.
+	 * And the opener of the id file also had the approprpiate capability.
+	 */
+	if (ns_capable(ns->parent, cap_setid) &&
+	    file_ns_capable(file, ns->parent, cap_setid))
+		return true;
+
+	return false;
+}
+
+int proc_setgroups_show(struct seq_file *seq, void *v)
+{
+	struct user_namespace *ns = seq->private;
+	unsigned long userns_flags = READ_ONCE(ns->flags);
+
+	seq_printf(seq, "%s\n",
+		   (userns_flags & USERNS_SETGROUPS_ALLOWED) ?
+		   "allow" : "deny");
+	return 0;
+}
+
+ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
+			     size_t count, loff_t *ppos)
+{
+	struct seq_file *seq = file->private_data;
+	struct user_namespace *ns = seq->private;
+	char kbuf[8], *pos;
+	bool setgroups_allowed;
+	ssize_t ret;
+
+	/* Only allow a very narrow range of strings to be written */
+	ret = -EINVAL;
+	if ((*ppos != 0) || (count >= sizeof(kbuf)))
+		goto out;
+
+	/* What was written? */
+	ret = -EFAULT;
+	if (copy_from_user(kbuf, buf, count))
+		goto out;
+	kbuf[count] = '\0';
+	pos = kbuf;
+
+	/* What is being requested? */
+	ret = -EINVAL;
+	if (strncmp(pos, "allow", 5) == 0) {
+		pos += 5;
+		setgroups_allowed = true;
+	}
+	else if (strncmp(pos, "deny", 4) == 0) {
+		pos += 4;
+		setgroups_allowed = false;
+	}
+	else
+		goto out;
+
+	/* Verify there is not trailing junk on the line */
+	pos = skip_spaces(pos);
+	if (*pos != '\0')
+		goto out;
+
+	ret = -EPERM;
+	mutex_lock(&userns_state_mutex);
+	if (setgroups_allowed) {
+		/* Enabling setgroups after setgroups has been disabled
+		 * is not allowed.
+		 */
+		if (!(ns->flags & USERNS_SETGROUPS_ALLOWED))
+			goto out_unlock;
+	} else {
+		/* Permanently disabling setgroups after setgroups has
+		 * been enabled by writing the gid_map is not allowed.
+		 */
+		if (ns->gid_map.nr_extents != 0)
+			goto out_unlock;
+		ns->flags &= ~USERNS_SETGROUPS_ALLOWED;
+	}
+	mutex_unlock(&userns_state_mutex);
+
+	/* Report a successful write */
+	*ppos = count;
+	ret = count;
+out:
+	return ret;
+out_unlock:
+	mutex_unlock(&userns_state_mutex);
+	goto out;
+}
+
+bool userns_may_setgroups(const struct user_namespace *ns)
+{
+	bool allowed;
+
+	mutex_lock(&userns_state_mutex);
+	/* It is not safe to use setgroups until a gid mapping in
+	 * the user namespace has been established.
+	 */
+	allowed = ns->gid_map.nr_extents != 0;
+	/* Is setgroups allowed? */
+	allowed = allowed && (ns->flags & USERNS_SETGROUPS_ALLOWED);
+	mutex_unlock(&userns_state_mutex);
+
+	return allowed;
+}
+
+/*
+ * Returns true if @child is the same namespace or a descendant of
+ * @ancestor.
+ */
+bool in_userns(const struct user_namespace *ancestor,
+	       const struct user_namespace *child)
+{
+	const struct user_namespace *ns;
+	for (ns = child; ns->level > ancestor->level; ns = ns->parent)
+		;
+	return (ns == ancestor);
+}
+
+bool current_in_userns(const struct user_namespace *target_ns)
+{
+	return in_userns(target_ns, current_user_ns());
+}
+EXPORT_SYMBOL(current_in_userns);
+
+static inline struct user_namespace *to_user_ns(struct ns_common *ns)
+{
+	return container_of(ns, struct user_namespace, ns);
+}
+
+static struct ns_common *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 ? &user_ns->ns : NULL;
+}
+
+static void userns_put(struct ns_common *ns)
+{
+	put_user_ns(to_user_ns(ns));
+}
+
+static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
+{
+	struct user_namespace *user_ns = to_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;
+
+	/* Tasks that share a thread group must share a user namespace */
+	if (!thread_group_empty(current))
+		return -EINVAL;
+
+	if (current->fs->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);
+}
+
+struct ns_common *ns_get_owner(struct ns_common *ns)
+{
+	struct user_namespace *my_user_ns = current_user_ns();
+	struct user_namespace *owner, *p;
+
+	/* See if the owner is in the current user namespace */
+	owner = p = ns->ops->owner(ns);
+	for (;;) {
+		if (!p)
+			return ERR_PTR(-EPERM);
+		if (p == my_user_ns)
+			break;
+		p = p->parent;
+	}
+
+	return &get_user_ns(owner)->ns;
+}
+
+static struct user_namespace *userns_owner(struct ns_common *ns)
+{
+	return to_user_ns(ns)->parent;
+}
+
+const struct proc_ns_operations userns_operations = {
+	.name		= "user",
+	.type		= CLONE_NEWUSER,
+	.get		= userns_get,
+	.put		= userns_put,
+	.install	= userns_install,
+	.owner		= userns_owner,
+	.get_parent	= ns_get_owner,
+};
+
+static __init int user_namespaces_init(void)
+{
+	user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
+	return 0;
+}
+subsys_initcall(user_namespaces_init);