Merge branch 'linux-4.15' of git://github.com/skeggsb/linux into drm-fixes

[mirror_ubuntu-bionic-kernel.git] / 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/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(sizeof(struct uid_gid_extent) *
                                 UID_GID_MAP_MAX_EXTENTS, 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 = -EINVAL;

        /*
         * 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;

        /* 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 */
        kbuf = memdup_user_nul(buf, count);
        if (IS_ERR(kbuf)) {
                ret = PTR_ERR(kbuf);
                kbuf = NULL;
                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 = sort_idmaps(&new_map);
        if (ret < 0)
                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;
        }

        /* 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());
}

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);