Quelle user_namespace.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only

#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/security.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 __ro_after_init;
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;
}

static unsigned long enforced_nproc_rlimit(void)
{
unsigned long limit = RLIM_INFINITY;

/* Is RLIMIT_NPROC currently enforced? */
if (!uid_eq(current_uid(), GLOBAL_ROOT_UID) ||
     (current_user_ns() != &init_user_ns))
  limit = rlimit(RLIMIT_NPROC);

return limit;
}

/*
* 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 verifying 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 = security_create_user_ns(new);
if (ret < 0)
  goto fail_dec;

ret = -ENOMEM;
ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
if (!ns)
  goto fail_dec;

ns->parent_could_setfcap = cap_raised(new->cap_effective, CAP_SETFCAP);
ret = ns_alloc_inum(&ns->ns);
if (ret)
  goto fail_free;
ns->ns.ops = &userns_operations;

refcount_set(&ns->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;
}
set_userns_rlimit_max(ns, UCOUNT_RLIMIT_NPROC, enforced_nproc_rlimit());
set_userns_rlimit_max(ns, UCOUNT_RLIMIT_MSGQUEUE, rlimit(RLIMIT_MSGQUEUE));
set_userns_rlimit_max(ns, UCOUNT_RLIMIT_SIGPENDING, rlimit(RLIMIT_SIGPENDING));
set_userns_rlimit_max(ns, UCOUNT_RLIMIT_MEMLOCK, rlimit(RLIMIT_MEMLOCK));
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_KEYS
INIT_LIST_HEAD(&ns->keyring_name_list);
init_rwsem(&ns->keyring_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);
  }
#if IS_ENABLED(CONFIG_BINFMT_MISC)
  kfree(ns->binfmt_misc);
#endif
  retire_userns_sysctls(ns);
  key_free_user_ns(ns);
  ns_free_inum(&ns->ns);
  kmem_cache_free(user_ns_cachep, ns);
  dec_user_namespaces(ucounts);
  ns = parent;
} while (refcount_dec_and_test(&parent->ns.count));
}

void __put_user_ns(struct user_namespace *ns)
{
schedule_work(&ns->work);
}
EXPORT_SYMBOL(__put_user_ns);

/*
* struct idmap_key - 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;
};

/*
* 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;
}

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_range_up_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].lower_first;
  last = first + map->extent[idx].count - 1;
  if (id >= first && id <= last &&
      (id2 >= first && id2 <= 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_range_up_max(unsigned extents, struct uid_gid_map *map, u32 id, u32 count)
{
struct idmap_key key;

key.map_up = true;
key.count = count;
key.id = id;

return bsearch(&key, map->reverse, extents,
         sizeof(struct uid_gid_extent), cmp_map_id);
}

u32 map_id_range_up(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_up_base(extents, map, id, count);
else
  extent = map_id_range_up_max(extents, map, id, count);

/* Map the id or note failure */
if (extent)
  id = (id - extent->lower_first) + extent->first;
else
  id = (u32) -1;

return id;
}

u32 map_id_up(struct uid_gid_map *map, u32 id)
{
return map_id_range_up(map, id, 1);
}

/**
* 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 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_array(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;
}

/**
* verify_root_map() - check the uid 0 mapping
* @file: idmapping file
* @map_ns: user namespace of the target process
* @new_map: requested idmap
*
* If a process requests mapping parent uid 0 into the new ns, verify that the
* process writing the map had the CAP_SETFCAP capability as the target process
* will be able to write fscaps that are valid in ancestor user namespaces.
*
* Return: true if the mapping is allowed, false if not.
*/
static bool verify_root_map(const struct file *file,
       struct user_namespace *map_ns,
       struct uid_gid_map *new_map)
{
int idx;
const struct user_namespace *file_ns = file->f_cred->user_ns;
struct uid_gid_extent *extent0 = NULL;

for (idx = 0; idx < new_map->nr_extents; idx++) {
  if (new_map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
   extent0 = &new_map->extent[idx];
  else
   extent0 = &new_map->forward[idx];
  if (extent0->lower_first == 0)
   break;

  extent0 = NULL;
}

if (!extent0)
  return true;

if (map_ns == file_ns) {
  /* The process unshared its ns and is writing to its own
* /proc/self/uid_map.  User already has full capabilites in
* the new namespace.  Verify that the parent had CAP_SETFCAP
* when it unshared.
* */
  if (!file_ns->parent_could_setfcap)
   return false;
} else {
  /* Process p1 is writing to uid_map of p2, who is in a child
* user namespace to p1's.  Verify that the opener of the map
* file has CAP_SETFCAP against the parent of the new map
* namespace */
  if (!file_ns_capable(file, map_ns->parent, CAP_SETFCAP))
   return false;
}

return true;
}

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 *map_ns = seq->private;
struct uid_gid_map new_map;
unsigned idx;
struct uid_gid_extent extent;
char *kbuf, *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, map_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 certain 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, map_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;

if (cap_setid == CAP_SETUID && !verify_root_map(file, ns, new_map))
  return false;

/* 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 has the appropriate 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 nsset *nsset, 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 = nsset_cred(nsset);
if (!cred)
  return -EINVAL;

put_user_ns(cred->user_ns);
set_cred_user_ns(cred, get_user_ns(user_ns));

if (set_cred_ucounts(cred) < 0)
  return -EINVAL;

return 0;
}

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 | SLAB_ACCOUNT);
return 0;
}
subsys_initcall(user_namespaces_init);

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