/*
   * NetLabel Domain Hash Table
   *
   * This file manages the domain hash table that NetLabel uses to determine
   * which network labeling protocol to use for a given domain.  The NetLabel
   * system manages static and dynamic label mappings for network protocols such
   * as CIPSO and RIPSO.
   *

   * Author: Paul Moore <paul@paul-moore.com>

   *
   */
  
  /*

   * (c) Copyright Hewlett-Packard Development Company, L.P., 2006, 2008

   *
   * 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; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY;  without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
   * the GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program;  if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
   *
   */
  
  #include <linux/types.h>

  #include <linux/rculist.h>

  #include <linux/skbuff.h>
  #include <linux/spinlock.h>
  #include <linux/string.h>

  #include <linux/audit.h>

  #include <linux/slab.h>

  #include <net/netlabel.h>
  #include <net/cipso_ipv4.h>
  #include <asm/bug.h>
  
  #include "netlabel_mgmt.h"

  #include "netlabel_addrlist.h"

  #include "netlabel_domainhash.h"

  #include "netlabel_user.h"

  
  struct netlbl_domhsh_tbl {
  	struct list_head *tbl;
  	u32 size;
  };
  
  /* Domain hash table */

  /* updates should be so rare that having one spinlock for the entire hash table
   * should be okay */

  static DEFINE_SPINLOCK(netlbl_domhsh_lock);

  #define netlbl_domhsh_rcu_deref(p) \

  	rcu_dereference_check(p, lockdep_is_held(&netlbl_domhsh_lock))

  static struct netlbl_domhsh_tbl *netlbl_domhsh = NULL;

  static struct netlbl_dom_map *netlbl_domhsh_def = NULL;
  
  /*
   * Domain Hash Table Helper Functions
   */
  
  /**
   * netlbl_domhsh_free_entry - Frees a domain hash table entry
   * @entry: the entry's RCU field
   *
   * Description:
   * This function is designed to be used as a callback to the call_rcu()
   * function so that the memory allocated to a hash table entry can be released
   * safely.
   *
   */
  static void netlbl_domhsh_free_entry(struct rcu_head *entry)
  {
  	struct netlbl_dom_map *ptr;

  	struct netlbl_af4list *iter4;
  	struct netlbl_af4list *tmp4;

  #if IS_ENABLED(CONFIG_IPV6)

  	struct netlbl_af6list *iter6;
  	struct netlbl_af6list *tmp6;
  #endif /* IPv6 */

  
  	ptr = container_of(entry, struct netlbl_dom_map, rcu);

  	if (ptr->type == NETLBL_NLTYPE_ADDRSELECT) {
  		netlbl_af4list_foreach_safe(iter4, tmp4,
  					    &ptr->type_def.addrsel->list4) {
  			netlbl_af4list_remove_entry(iter4);
  			kfree(netlbl_domhsh_addr4_entry(iter4));
  		}

  #if IS_ENABLED(CONFIG_IPV6)

  		netlbl_af6list_foreach_safe(iter6, tmp6,
  					    &ptr->type_def.addrsel->list6) {
  			netlbl_af6list_remove_entry(iter6);
  			kfree(netlbl_domhsh_addr6_entry(iter6));
  		}
  #endif /* IPv6 */
  	}

  	kfree(ptr->domain);
  	kfree(ptr);
  }
  
  /**
   * netlbl_domhsh_hash - Hashing function for the domain hash table
   * @domain: the domain name to hash
   *
   * Description:
   * This is the hashing function for the domain hash table, it returns the

   * correct bucket number for the domain.  The caller is responsible for

   * ensuring that the hash table is protected with either a RCU read lock or the
   * hash table lock.

   *
   */
  static u32 netlbl_domhsh_hash(const char *key)
  {
  	u32 iter;
  	u32 val;
  	u32 len;
  
  	/* This is taken (with slight modification) from
  	 * security/selinux/ss/symtab.c:symhash() */
  
  	for (iter = 0, val = 0, len = strlen(key); iter < len; iter++)
  		val = (val << 4 | (val >> (8 * sizeof(u32) - 4))) ^ key[iter];

  	return val & (netlbl_domhsh_rcu_deref(netlbl_domhsh)->size - 1);

  }
  
  /**
   * netlbl_domhsh_search - Search for a domain entry
   * @domain: the domain

   *
   * Description:
   * Searches the domain hash table and returns a pointer to the hash table

   * entry if found, otherwise NULL is returned.  The caller is responsible for

   * ensuring that the hash table is protected with either a RCU read lock or the
   * hash table lock.

   *
   */

  static struct netlbl_dom_map *netlbl_domhsh_search(const char *domain)

  {
  	u32 bkt;

  	struct list_head *bkt_list;

  	struct netlbl_dom_map *iter;
  
  	if (domain != NULL) {
  		bkt = netlbl_domhsh_hash(domain);

  		bkt_list = &netlbl_domhsh_rcu_deref(netlbl_domhsh)->tbl[bkt];

  		list_for_each_entry_rcu(iter, bkt_list, list)

  			if (iter->valid && strcmp(iter->domain, domain) == 0)
  				return iter;
  	}

  	return NULL;
  }
  
  /**
   * netlbl_domhsh_search_def - Search for a domain entry
   * @domain: the domain
   * @def: return default if no match is found
   *
   * Description:
   * Searches the domain hash table and returns a pointer to the hash table
   * entry if an exact match is found, if an exact match is not present in the
   * hash table then the default entry is returned if valid otherwise NULL is

   * returned.  The caller is responsible ensuring that the hash table is

   * protected with either a RCU read lock or the hash table lock.

   *
   */
  static struct netlbl_dom_map *netlbl_domhsh_search_def(const char *domain)
  {
  	struct netlbl_dom_map *entry;
  
  	entry = netlbl_domhsh_search(domain);
  	if (entry == NULL) {

  		entry = netlbl_domhsh_rcu_deref(netlbl_domhsh_def);

  		if (entry != NULL && !entry->valid)
  			entry = NULL;

  	}

  	return entry;

  }

  /**
   * netlbl_domhsh_audit_add - Generate an audit entry for an add event
   * @entry: the entry being added
   * @addr4: the IPv4 address information
   * @addr6: the IPv6 address information
   * @result: the result code
   * @audit_info: NetLabel audit information
   *
   * Description:
   * Generate an audit record for adding a new NetLabel/LSM mapping entry with

   * the given information.  Caller is responsible for holding the necessary

   * locks.
   *
   */
  static void netlbl_domhsh_audit_add(struct netlbl_dom_map *entry,
  				    struct netlbl_af4list *addr4,
  				    struct netlbl_af6list *addr6,
  				    int result,
  				    struct netlbl_audit *audit_info)
  {
  	struct audit_buffer *audit_buf;
  	struct cipso_v4_doi *cipsov4 = NULL;
  	u32 type;
  
  	audit_buf = netlbl_audit_start_common(AUDIT_MAC_MAP_ADD, audit_info);
  	if (audit_buf != NULL) {
  		audit_log_format(audit_buf, " nlbl_domain=%s",
  				 entry->domain ? entry->domain : "(default)");
  		if (addr4 != NULL) {
  			struct netlbl_domaddr4_map *map4;
  			map4 = netlbl_domhsh_addr4_entry(addr4);
  			type = map4->type;
  			cipsov4 = map4->type_def.cipsov4;
  			netlbl_af4list_audit_addr(audit_buf, 0, NULL,
  						  addr4->addr, addr4->mask);

  #if IS_ENABLED(CONFIG_IPV6)

  		} else if (addr6 != NULL) {
  			struct netlbl_domaddr6_map *map6;
  			map6 = netlbl_domhsh_addr6_entry(addr6);
  			type = map6->type;
  			netlbl_af6list_audit_addr(audit_buf, 0, NULL,
  						  &addr6->addr, &addr6->mask);
  #endif /* IPv6 */
  		} else {
  			type = entry->type;
  			cipsov4 = entry->type_def.cipsov4;
  		}
  		switch (type) {
  		case NETLBL_NLTYPE_UNLABELED:
  			audit_log_format(audit_buf, " nlbl_protocol=unlbl");
  			break;
  		case NETLBL_NLTYPE_CIPSOV4:
  			BUG_ON(cipsov4 == NULL);
  			audit_log_format(audit_buf,
  					 " nlbl_protocol=cipsov4 cipso_doi=%u",
  					 cipsov4->doi);
  			break;
  		}
  		audit_log_format(audit_buf, " res=%u", result == 0 ? 1 : 0);
  		audit_log_end(audit_buf);
  	}
  }

  /*
   * Domain Hash Table Functions
   */
  
  /**
   * netlbl_domhsh_init - Init for the domain hash
   * @size: the number of bits to use for the hash buckets
   *
   * Description:
   * Initializes the domain hash table, should be called only by
   * netlbl_user_init() during initialization.  Returns zero on success, non-zero
   * values on error.
   *
   */

  int __init netlbl_domhsh_init(u32 size)

  {
  	u32 iter;
  	struct netlbl_domhsh_tbl *hsh_tbl;
  
  	if (size == 0)
  		return -EINVAL;
  
  	hsh_tbl = kmalloc(sizeof(*hsh_tbl), GFP_KERNEL);
  	if (hsh_tbl == NULL)
  		return -ENOMEM;
  	hsh_tbl->size = 1 << size;
  	hsh_tbl->tbl = kcalloc(hsh_tbl->size,
  			       sizeof(struct list_head),
  			       GFP_KERNEL);
  	if (hsh_tbl->tbl == NULL) {
  		kfree(hsh_tbl);
  		return -ENOMEM;
  	}
  	for (iter = 0; iter < hsh_tbl->size; iter++)
  		INIT_LIST_HEAD(&hsh_tbl->tbl[iter]);

  	spin_lock(&netlbl_domhsh_lock);

  	rcu_assign_pointer(netlbl_domhsh, hsh_tbl);

  	spin_unlock(&netlbl_domhsh_lock);

  
  	return 0;
  }
  
  /**
   * netlbl_domhsh_add - Adds a entry to the domain hash table
   * @entry: the entry to add

   * @audit_info: NetLabel audit information

   *
   * Description:
   * Adds a new entry to the domain hash table and handles any updates to the
   * lower level protocol handler (i.e. CIPSO).  Returns zero on success,
   * negative on failure.
   *
   */

  int netlbl_domhsh_add(struct netlbl_dom_map *entry,
  		      struct netlbl_audit *audit_info)

  {

  	int ret_val = 0;
  	struct netlbl_dom_map *entry_old;
  	struct netlbl_af4list *iter4;
  	struct netlbl_af4list *tmp4;

  #if IS_ENABLED(CONFIG_IPV6)

  	struct netlbl_af6list *iter6;
  	struct netlbl_af6list *tmp6;
  #endif /* IPv6 */

  	/* XXX - we can remove this RCU read lock as the spinlock protects the
  	 *       entire function, but before we do we need to fixup the
  	 *       netlbl_af[4,6]list RCU functions to do "the right thing" with
  	 *       respect to rcu_dereference() when only a spinlock is held. */

  	rcu_read_lock();

  	spin_lock(&netlbl_domhsh_lock);

  	if (entry->domain != NULL)
  		entry_old = netlbl_domhsh_search(entry->domain);
  	else
  		entry_old = netlbl_domhsh_search_def(entry->domain);
  	if (entry_old == NULL) {
  		entry->valid = 1;

  
  		if (entry->domain != NULL) {
  			u32 bkt = netlbl_domhsh_hash(entry->domain);

  			list_add_tail_rcu(&entry->list,

  				    &rcu_dereference(netlbl_domhsh)->tbl[bkt]);

  		} else {
  			INIT_LIST_HEAD(&entry->list);

  			rcu_assign_pointer(netlbl_domhsh_def, entry);

  		}

  		if (entry->type == NETLBL_NLTYPE_ADDRSELECT) {
  			netlbl_af4list_foreach_rcu(iter4,
  					       &entry->type_def.addrsel->list4)
  				netlbl_domhsh_audit_add(entry, iter4, NULL,
  							ret_val, audit_info);

  #if IS_ENABLED(CONFIG_IPV6)

  			netlbl_af6list_foreach_rcu(iter6,
  					       &entry->type_def.addrsel->list6)
  				netlbl_domhsh_audit_add(entry, NULL, iter6,
  							ret_val, audit_info);
  #endif /* IPv6 */
  		} else
  			netlbl_domhsh_audit_add(entry, NULL, NULL,
  						ret_val, audit_info);
  	} else if (entry_old->type == NETLBL_NLTYPE_ADDRSELECT &&
  		   entry->type == NETLBL_NLTYPE_ADDRSELECT) {
  		struct list_head *old_list4;
  		struct list_head *old_list6;
  
  		old_list4 = &entry_old->type_def.addrsel->list4;
  		old_list6 = &entry_old->type_def.addrsel->list6;
  
  		/* we only allow the addition of address selectors if all of
  		 * the selectors do not exist in the existing domain map */
  		netlbl_af4list_foreach_rcu(iter4,
  					   &entry->type_def.addrsel->list4)
  			if (netlbl_af4list_search_exact(iter4->addr,
  							iter4->mask,
  							old_list4)) {
  				ret_val = -EEXIST;
  				goto add_return;
  			}

  #if IS_ENABLED(CONFIG_IPV6)

  		netlbl_af6list_foreach_rcu(iter6,
  					   &entry->type_def.addrsel->list6)
  			if (netlbl_af6list_search_exact(&iter6->addr,
  							&iter6->mask,
  							old_list6)) {
  				ret_val = -EEXIST;
  				goto add_return;
  			}
  #endif /* IPv6 */
  
  		netlbl_af4list_foreach_safe(iter4, tmp4,
  					    &entry->type_def.addrsel->list4) {
  			netlbl_af4list_remove_entry(iter4);
  			iter4->valid = 1;
  			ret_val = netlbl_af4list_add(iter4, old_list4);
  			netlbl_domhsh_audit_add(entry_old, iter4, NULL,
  						ret_val, audit_info);
  			if (ret_val != 0)
  				goto add_return;
  		}

  #if IS_ENABLED(CONFIG_IPV6)

  		netlbl_af6list_foreach_safe(iter6, tmp6,
  					    &entry->type_def.addrsel->list6) {
  			netlbl_af6list_remove_entry(iter6);
  			iter6->valid = 1;
  			ret_val = netlbl_af6list_add(iter6, old_list6);
  			netlbl_domhsh_audit_add(entry_old, NULL, iter6,
  						ret_val, audit_info);
  			if (ret_val != 0)
  				goto add_return;
  		}
  #endif /* IPv6 */
  	} else
  		ret_val = -EINVAL;
  
  add_return:
  	spin_unlock(&netlbl_domhsh_lock);
  	rcu_read_unlock();

  	return ret_val;
  }
  
  /**
   * netlbl_domhsh_add_default - Adds the default entry to the domain hash table
   * @entry: the entry to add

   * @audit_info: NetLabel audit information

   *
   * Description:
   * Adds a new default entry to the domain hash table and handles any updates
   * to the lower level protocol handler (i.e. CIPSO).  Returns zero on success,
   * negative on failure.
   *
   */

  int netlbl_domhsh_add_default(struct netlbl_dom_map *entry,
  			      struct netlbl_audit *audit_info)

  {

  	return netlbl_domhsh_add(entry, audit_info);

  }
  
  /**

   * netlbl_domhsh_remove_entry - Removes a given entry from the domain table
   * @entry: the entry to remove

   * @audit_info: NetLabel audit information

   *
   * Description:
   * Removes an entry from the domain hash table and handles any updates to the

   * lower level protocol handler (i.e. CIPSO).  Caller is responsible for
   * ensuring that the RCU read lock is held.  Returns zero on success, negative
   * on failure.

   *
   */

  int netlbl_domhsh_remove_entry(struct netlbl_dom_map *entry,
  			       struct netlbl_audit *audit_info)

  {

  	int ret_val = 0;

  	struct audit_buffer *audit_buf;

  	if (entry == NULL)

  		return -ENOENT;

  	spin_lock(&netlbl_domhsh_lock);
  	if (entry->valid) {
  		entry->valid = 0;
  		if (entry != rcu_dereference(netlbl_domhsh_def))

  			list_del_rcu(&entry->list);

  		else

  			RCU_INIT_POINTER(netlbl_domhsh_def, NULL);

  	} else
  		ret_val = -ENOENT;

  	spin_unlock(&netlbl_domhsh_lock);

  	audit_buf = netlbl_audit_start_common(AUDIT_MAC_MAP_DEL, audit_info);

  	if (audit_buf != NULL) {
  		audit_log_format(audit_buf,
  				 " nlbl_domain=%s res=%u",
  				 entry->domain ? entry->domain : "(default)",
  				 ret_val == 0 ? 1 : 0);
  		audit_log_end(audit_buf);
  	}

  	if (ret_val == 0) {

  		struct netlbl_af4list *iter4;
  		struct netlbl_domaddr4_map *map4;

  		switch (entry->type) {

  		case NETLBL_NLTYPE_ADDRSELECT:
  			netlbl_af4list_foreach_rcu(iter4,
  					     &entry->type_def.addrsel->list4) {
  				map4 = netlbl_domhsh_addr4_entry(iter4);
  				cipso_v4_doi_putdef(map4->type_def.cipsov4);
  			}
  			/* no need to check the IPv6 list since we currently
  			 * support only unlabeled protocols for IPv6 */
  			break;

  		case NETLBL_NLTYPE_CIPSOV4:
  			cipso_v4_doi_putdef(entry->type_def.cipsov4);
  			break;
  		}

  		call_rcu(&entry->rcu, netlbl_domhsh_free_entry);

  	}
  
  	return ret_val;
  }
  
  /**

   * netlbl_domhsh_remove_af4 - Removes an address selector entry
   * @domain: the domain
   * @addr: IPv4 address
   * @mask: IPv4 address mask
   * @audit_info: NetLabel audit information
   *
   * Description:
   * Removes an individual address selector from a domain mapping and potentially
   * the entire mapping if it is empty.  Returns zero on success, negative values
   * on failure.
   *
   */
  int netlbl_domhsh_remove_af4(const char *domain,
  			     const struct in_addr *addr,
  			     const struct in_addr *mask,
  			     struct netlbl_audit *audit_info)
  {
  	struct netlbl_dom_map *entry_map;
  	struct netlbl_af4list *entry_addr;
  	struct netlbl_af4list *iter4;

  #if IS_ENABLED(CONFIG_IPV6)

  	struct netlbl_af6list *iter6;
  #endif /* IPv6 */
  	struct netlbl_domaddr4_map *entry;
  
  	rcu_read_lock();
  
  	if (domain)
  		entry_map = netlbl_domhsh_search(domain);
  	else
  		entry_map = netlbl_domhsh_search_def(domain);
  	if (entry_map == NULL || entry_map->type != NETLBL_NLTYPE_ADDRSELECT)
  		goto remove_af4_failure;
  
  	spin_lock(&netlbl_domhsh_lock);
  	entry_addr = netlbl_af4list_remove(addr->s_addr, mask->s_addr,
  					   &entry_map->type_def.addrsel->list4);
  	spin_unlock(&netlbl_domhsh_lock);
  
  	if (entry_addr == NULL)
  		goto remove_af4_failure;
  	netlbl_af4list_foreach_rcu(iter4, &entry_map->type_def.addrsel->list4)
  		goto remove_af4_single_addr;

  #if IS_ENABLED(CONFIG_IPV6)

  	netlbl_af6list_foreach_rcu(iter6, &entry_map->type_def.addrsel->list6)
  		goto remove_af4_single_addr;
  #endif /* IPv6 */
  	/* the domain mapping is empty so remove it from the mapping table */
  	netlbl_domhsh_remove_entry(entry_map, audit_info);
  
  remove_af4_single_addr:
  	rcu_read_unlock();
  	/* yick, we can't use call_rcu here because we don't have a rcu head
  	 * pointer but hopefully this should be a rare case so the pause
  	 * shouldn't be a problem */
  	synchronize_rcu();
  	entry = netlbl_domhsh_addr4_entry(entry_addr);
  	cipso_v4_doi_putdef(entry->type_def.cipsov4);
  	kfree(entry);
  	return 0;
  
  remove_af4_failure:
  	rcu_read_unlock();
  	return -ENOENT;
  }
  
  /**

   * netlbl_domhsh_remove - Removes an entry from the domain hash table
   * @domain: the domain to remove
   * @audit_info: NetLabel audit information
   *
   * Description:
   * Removes an entry from the domain hash table and handles any updates to the
   * lower level protocol handler (i.e. CIPSO).  Returns zero on success,
   * negative on failure.
   *
   */
  int netlbl_domhsh_remove(const char *domain, struct netlbl_audit *audit_info)
  {
  	int ret_val;
  	struct netlbl_dom_map *entry;
  
  	rcu_read_lock();
  	if (domain)
  		entry = netlbl_domhsh_search(domain);
  	else
  		entry = netlbl_domhsh_search_def(domain);
  	ret_val = netlbl_domhsh_remove_entry(entry, audit_info);
  	rcu_read_unlock();

  	return ret_val;
  }
  
  /**
   * netlbl_domhsh_remove_default - Removes the default entry from the table

   * @audit_info: NetLabel audit information

   *
   * Description:
   * Removes/resets the default entry for the domain hash table and handles any
   * updates to the lower level protocol handler (i.e. CIPSO).  Returns zero on
   * success, non-zero on failure.
   *
   */

  int netlbl_domhsh_remove_default(struct netlbl_audit *audit_info)

  {

  	return netlbl_domhsh_remove(NULL, audit_info);

  }
  
  /**
   * netlbl_domhsh_getentry - Get an entry from the domain hash table
   * @domain: the domain name to search for
   *
   * Description:
   * Look through the domain hash table searching for an entry to match @domain,

   * return a pointer to a copy of the entry or NULL.  The caller is responsible

   * for ensuring that rcu_read_[un]lock() is called.
   *
   */
  struct netlbl_dom_map *netlbl_domhsh_getentry(const char *domain)
  {

  	return netlbl_domhsh_search_def(domain);

  }
  
  /**

   * netlbl_domhsh_getentry_af4 - Get an entry from the domain hash table
   * @domain: the domain name to search for
   * @addr: the IP address to search for
   *
   * Description:
   * Look through the domain hash table searching for an entry to match @domain
   * and @addr, return a pointer to a copy of the entry or NULL.  The caller is
   * responsible for ensuring that rcu_read_[un]lock() is called.
   *
   */
  struct netlbl_domaddr4_map *netlbl_domhsh_getentry_af4(const char *domain,
  						       __be32 addr)
  {
  	struct netlbl_dom_map *dom_iter;
  	struct netlbl_af4list *addr_iter;
  
  	dom_iter = netlbl_domhsh_search_def(domain);
  	if (dom_iter == NULL)
  		return NULL;
  	if (dom_iter->type != NETLBL_NLTYPE_ADDRSELECT)
  		return NULL;
  
  	addr_iter = netlbl_af4list_search(addr,
  					  &dom_iter->type_def.addrsel->list4);
  	if (addr_iter == NULL)
  		return NULL;
  
  	return netlbl_domhsh_addr4_entry(addr_iter);
  }

  #if IS_ENABLED(CONFIG_IPV6)

  /**
   * netlbl_domhsh_getentry_af6 - Get an entry from the domain hash table
   * @domain: the domain name to search for
   * @addr: the IP address to search for
   *
   * Description:
   * Look through the domain hash table searching for an entry to match @domain
   * and @addr, return a pointer to a copy of the entry or NULL.  The caller is
   * responsible for ensuring that rcu_read_[un]lock() is called.
   *
   */
  struct netlbl_domaddr6_map *netlbl_domhsh_getentry_af6(const char *domain,
  						   const struct in6_addr *addr)
  {
  	struct netlbl_dom_map *dom_iter;
  	struct netlbl_af6list *addr_iter;
  
  	dom_iter = netlbl_domhsh_search_def(domain);
  	if (dom_iter == NULL)
  		return NULL;
  	if (dom_iter->type != NETLBL_NLTYPE_ADDRSELECT)
  		return NULL;
  
  	addr_iter = netlbl_af6list_search(addr,
  					  &dom_iter->type_def.addrsel->list6);
  	if (addr_iter == NULL)
  		return NULL;
  
  	return netlbl_domhsh_addr6_entry(addr_iter);
  }
  #endif /* IPv6 */
  
  /**

   * netlbl_domhsh_walk - Iterate through the domain mapping hash table
   * @skip_bkt: the number of buckets to skip at the start
   * @skip_chain: the number of entries to skip in the first iterated bucket
   * @callback: callback for each entry
   * @cb_arg: argument for the callback function

   *
   * Description:

   * Interate over the domain mapping hash table, skipping the first @skip_bkt
   * buckets and @skip_chain entries.  For each entry in the table call
   * @callback, if @callback returns a negative value stop 'walking' through the
   * table and return.  Updates the values in @skip_bkt and @skip_chain on

   * return.  Returns zero on success, negative values on failure.

   *
   */

  int netlbl_domhsh_walk(u32 *skip_bkt,
  		     u32 *skip_chain,
  		     int (*callback) (struct netlbl_dom_map *entry, void *arg),
  		     void *cb_arg)

  {

  	int ret_val = -ENOENT;
  	u32 iter_bkt;

  	struct list_head *iter_list;

  	struct netlbl_dom_map *iter_entry;
  	u32 chain_cnt = 0;

  	rcu_read_lock();

  	for (iter_bkt = *skip_bkt;
  	     iter_bkt < rcu_dereference(netlbl_domhsh)->size;
  	     iter_bkt++, chain_cnt = 0) {

  		iter_list = &rcu_dereference(netlbl_domhsh)->tbl[iter_bkt];
  		list_for_each_entry_rcu(iter_entry, iter_list, list)

  			if (iter_entry->valid) {
  				if (chain_cnt++ < *skip_chain)
  					continue;
  				ret_val = callback(iter_entry, cb_arg);
  				if (ret_val < 0) {
  					chain_cnt--;
  					goto walk_return;
  				}

  			}

  	}

  walk_return:

  	rcu_read_unlock();

  	*skip_bkt = iter_bkt;
  	*skip_chain = chain_cnt;
  	return ret_val;

  }