/*
   *  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/stat.h>
  #include <linux/sysctl.h>
  #include <linux/slab.h>

  #include <linux/hash.h>

  #include <linux/user_namespace.h>

  #define UCOUNTS_HASHTABLE_BITS 10
  static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
  static DEFINE_SPINLOCK(ucounts_lock);
  
  #define ucounts_hashfn(ns, uid)						\
  	hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
  		  UCOUNTS_HASHTABLE_BITS)
  #define ucounts_hashentry(ns, uid)	\
  	(ucounts_hashtable + ucounts_hashfn(ns, uid))

  #ifdef CONFIG_SYSCTL
  static struct ctl_table_set *
  set_lookup(struct ctl_table_root *root)
  {
  	return &current_user_ns()->set;
  }
  
  static int set_is_seen(struct ctl_table_set *set)
  {
  	return &current_user_ns()->set == set;
  }
  
  static int set_permissions(struct ctl_table_header *head,
  				  struct ctl_table *table)
  {
  	struct user_namespace *user_ns =
  		container_of(head->set, struct user_namespace, set);
  	int mode;
  
  	/* Allow users with CAP_SYS_RESOURCE unrestrained access */
  	if (ns_capable(user_ns, CAP_SYS_RESOURCE))
  		mode = (table->mode & S_IRWXU) >> 6;
  	else
  	/* Allow all others at most read-only access */
  		mode = table->mode & S_IROTH;
  	return (mode << 6) | (mode << 3) | mode;
  }
  
  static struct ctl_table_root set_root = {
  	.lookup = set_lookup,
  	.permissions = set_permissions,
  };

  static int zero = 0;
  static int int_max = INT_MAX;

  #define UCOUNT_ENTRY(name) 				\
  	{						\
  		.procname	= name,			\
  		.maxlen		= sizeof(int),		\
  		.mode		= 0644,			\
  		.proc_handler	= proc_dointvec_minmax,	\
  		.extra1		= &zero,		\
  		.extra2		= &int_max,		\
  	}

  static struct ctl_table user_table[] = {

  	UCOUNT_ENTRY("max_user_namespaces"),

  	UCOUNT_ENTRY("max_pid_namespaces"),

  	UCOUNT_ENTRY("max_uts_namespaces"),

  	UCOUNT_ENTRY("max_ipc_namespaces"),

  	UCOUNT_ENTRY("max_net_namespaces"),

  	UCOUNT_ENTRY("max_mnt_namespaces"),

  	UCOUNT_ENTRY("max_cgroup_namespaces"),

  	{ }
  };
  #endif /* CONFIG_SYSCTL */
  
  bool setup_userns_sysctls(struct user_namespace *ns)
  {
  #ifdef CONFIG_SYSCTL
  	struct ctl_table *tbl;
  	setup_sysctl_set(&ns->set, &set_root, set_is_seen);

  	tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);

  	if (tbl) {

  		int i;
  		for (i = 0; i < UCOUNT_COUNTS; i++) {
  			tbl[i].data = &ns->ucount_max[i];
  		}

  		ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);

  	}
  	if (!ns->sysctls) {
  		kfree(tbl);
  		retire_sysctl_set(&ns->set);
  		return false;
  	}
  #endif
  	return true;
  }
  
  void retire_userns_sysctls(struct user_namespace *ns)
  {
  #ifdef CONFIG_SYSCTL
  	struct ctl_table *tbl;
  
  	tbl = ns->sysctls->ctl_table_arg;
  	unregister_sysctl_table(ns->sysctls);
  	retire_sysctl_set(&ns->set);
  	kfree(tbl);
  #endif
  }

  static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
  {
  	struct ucounts *ucounts;
  
  	hlist_for_each_entry(ucounts, hashent, node) {
  		if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
  			return ucounts;
  	}
  	return NULL;
  }
  
  static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
  {
  	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
  	struct ucounts *ucounts, *new;

  	spin_lock_irq(&ucounts_lock);

  	ucounts = find_ucounts(ns, uid, hashent);
  	if (!ucounts) {

  		spin_unlock_irq(&ucounts_lock);

  
  		new = kzalloc(sizeof(*new), GFP_KERNEL);
  		if (!new)
  			return NULL;
  
  		new->ns = ns;
  		new->uid = uid;

  		new->count = 0;

  		spin_lock_irq(&ucounts_lock);

  		ucounts = find_ucounts(ns, uid, hashent);
  		if (ucounts) {
  			kfree(new);
  		} else {
  			hlist_add_head(&new->node, hashent);
  			ucounts = new;
  		}
  	}

  	if (ucounts->count == INT_MAX)

  		ucounts = NULL;

  	else
  		ucounts->count += 1;

  	spin_unlock_irq(&ucounts_lock);

  	return ucounts;
  }
  
  static void put_ucounts(struct ucounts *ucounts)
  {

  	unsigned long flags;

  	spin_lock_irqsave(&ucounts_lock, flags);
  	ucounts->count -= 1;
  	if (!ucounts->count)

  		hlist_del_init(&ucounts->node);

  	else
  		ucounts = NULL;
  	spin_unlock_irqrestore(&ucounts_lock, flags);

  	kfree(ucounts);

  }

  static inline bool atomic_inc_below(atomic_t *v, int u)
  {
  	int c, old;
  	c = atomic_read(v);
  	for (;;) {
  		if (unlikely(c >= u))
  			return false;
  		old = atomic_cmpxchg(v, c, c+1);
  		if (likely(old == c))
  			return true;
  		c = old;
  	}
  }

  struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
  			   enum ucount_type type)

  {

  	struct ucounts *ucounts, *iter, *bad;
  	struct user_namespace *tns;
  	ucounts = get_ucounts(ns, uid);
  	for (iter = ucounts; iter; iter = tns->ucounts) {
  		int max;
  		tns = iter->ns;

  		max = READ_ONCE(tns->ucount_max[type]);
  		if (!atomic_inc_below(&iter->ucount[type], max))

  			goto fail;
  	}

  	return ucounts;

  fail:

  	bad = iter;
  	for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)

  		atomic_dec(&iter->ucount[type]);

  	put_ucounts(ucounts);
  	return NULL;

  }

  void dec_ucount(struct ucounts *ucounts, enum ucount_type type)

  {

  	struct ucounts *iter;
  	for (iter = ucounts; iter; iter = iter->ns->ucounts) {

  		int dec = atomic_dec_if_positive(&iter->ucount[type]);

  		WARN_ON_ONCE(dec < 0);
  	}

  	put_ucounts(ucounts);

  }

  static __init int user_namespace_sysctl_init(void)
  {
  #ifdef CONFIG_SYSCTL

  	static struct ctl_table_header *user_header;

  	static struct ctl_table empty[1];
  	/*

  	 * It is necessary to register the user directory in the

  	 * default set so that registrations in the child sets work
  	 * properly.
  	 */

  	user_header = register_sysctl("user", empty);
  	BUG_ON(!user_header);

  	BUG_ON(!setup_userns_sysctls(&init_user_ns));
  #endif
  	return 0;
  }
  subsys_initcall(user_namespace_sysctl_init);