text: /*-
   * Copyright (c) 2001 Atsushi Onoe
   * Copyright (c) 2002-2005 Sam Leffler, Errno Consulting
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. The name of the author may not be used to endorse or promote products
   *    derived from this software without specific prior written permission.
   *
   * Alternatively, this software may be distributed under the terms of the
   * GNU General Public License ("GPL") version 2 as published by the Free
   * Software Foundation.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * $Id: ieee80211_crypto.c 1732 2006-09-24 21:06:25Z mentor $
   */
  #ifndef EXPORT_SYMTAB
  #define	EXPORT_SYMTAB
  #endif
  
  /*
   * IEEE 802.11 generic crypto support.
   */
  #ifndef AUTOCONF_INCLUDED
  #include <linux/config.h>
  #endif
  #include <linux/version.h>
  #include <linux/module.h>
  #include <linux/kmod.h>
  #include <linux/skbuff.h>
  #include <linux/netdevice.h>
  #include <linux/random.h>
  
  #include "if_ethersubr.h"		/* XXX ETHER_HDR_LEN */
  #include "if_media.h"
  
  #include <net80211/ieee80211_var.h>
  
  /*
   * Table of registered cipher modules.
   */
  static const struct ieee80211_cipher *ciphers[IEEE80211_CIPHER_MAX];
  
  static int _ieee80211_crypto_delkey(struct ieee80211vap *,
  	struct ieee80211_key *, struct ieee80211_node *);
  
  /*
   * Default "null" key management routines.
   */
  static int
  null_key_alloc(struct ieee80211vap *vap, const struct ieee80211_key *k)
  {
  	return IEEE80211_KEYIX_NONE;
  }
  static int
  null_key_delete(struct ieee80211vap *vap, const struct ieee80211_key *k,
  	struct ieee80211_node *ni)
  {
  	return 1;
  }
  static int
  null_key_set(struct ieee80211vap *vap, const struct ieee80211_key *k,
  	const u_int8_t mac[IEEE80211_ADDR_LEN])
  {
  	return 1;
  }
  static void null_key_update(struct ieee80211vap *vap)
  {
  }
  
  #ifdef ATH_SUPERG_COMP
  static void
  null_comp_set(struct ieee80211vap *vap, struct ieee80211_node *ni, 
  	int en)
  {
  }
  #endif
  
  /*
   * Write-arounds for common operations.
   */
  static __inline void
  cipher_detach(struct ieee80211_key *key)
  {
  	key->wk_cipher->ic_detach(key);
  }
  
  static __inline void *
  cipher_attach(struct ieee80211vap *vap, struct ieee80211_key *key)
  {
  	return key->wk_cipher->ic_attach(vap, key);
  }
  
  /* 
   * Wrappers for driver key management methods.
   */
  static __inline int
  dev_key_alloc(struct ieee80211vap *vap, const struct ieee80211_key *key)
  {
  	return vap->iv_key_alloc(vap, key);
  }
  
  static __inline int
  dev_key_delete(struct ieee80211vap *vap,	const struct ieee80211_key *key,
  	struct ieee80211_node *ni)
  {
  	return vap->iv_key_delete(vap, key, ni);
  }
  
  static __inline int
  dev_key_set(struct ieee80211vap *vap, const struct ieee80211_key *key,
  	const u_int8_t mac[IEEE80211_ADDR_LEN])
  {
  	return vap->iv_key_set(vap, key, mac);
  }
  
  #ifdef ATH_SUPERG_COMP
  static __inline void
  dev_comp_set(struct ieee80211vap *vap, struct ieee80211_node *ni, int en)
  {
  	return vap->iv_comp_set(vap, ni, en);
  }
  #endif
  
  /*
   * Setup crypto support for a device/shared instance.
   */
  void
  ieee80211_crypto_attach(struct ieee80211com *ic)
  {
  	/* NB: we assume everything is pre-zero'd */
  	ciphers[IEEE80211_CIPHER_NONE] = &ieee80211_cipher_none;
  }
  EXPORT_SYMBOL(ieee80211_crypto_attach);
  
  /*
   * Teardown crypto support.
   */
  void
  ieee80211_crypto_detach(struct ieee80211com *ic)
  {
  }
  EXPORT_SYMBOL(ieee80211_crypto_detach);
  
  /*
   * Setup crypto support for a vap.
   */
  void
  ieee80211_crypto_vattach(struct ieee80211vap *vap)
  {
  	int i;
  
  	/* NB: we assume everything is pre-zero'd */
  	vap->iv_def_txkey = IEEE80211_KEYIX_NONE;
  	for (i = 0; i < IEEE80211_WEP_NKID; i++)
  		ieee80211_crypto_resetkey(vap, &vap->iv_nw_keys[i],
  			IEEE80211_KEYIX_NONE);
  	/*
  	 * Initialize the driver key support routines to noop entries.
  	 * This is useful especially for the cipher test modules.
  	 */
  	vap->iv_key_alloc = null_key_alloc;
  	vap->iv_key_set = null_key_set;
  	vap->iv_key_delete = null_key_delete;
  	vap->iv_key_update_begin = null_key_update;
  	vap->iv_key_update_end = null_key_update;
  #ifdef ATH_SUPERG_COMP
  	vap->iv_comp_set = null_comp_set;
  #endif
  }
  EXPORT_SYMBOL(ieee80211_crypto_vattach);
  
  /*
   * Teardown crypto support for a vap.
   */
  void
  ieee80211_crypto_vdetach(struct ieee80211vap *vap)
  {
  	ieee80211_crypto_delglobalkeys(vap);
  }
  EXPORT_SYMBOL(ieee80211_crypto_vdetach);
  
  /*
   * Register a crypto cipher module.
   */
  void
  ieee80211_crypto_register(const struct ieee80211_cipher *cip)
  {
  	if (cip->ic_cipher >= IEEE80211_CIPHER_MAX) {
  		printf("%s: cipher %s has an invalid cipher index %u\n",
  			__func__, cip->ic_name, cip->ic_cipher);
  		return;
  	}
  	if (ciphers[cip->ic_cipher] != NULL && ciphers[cip->ic_cipher] != cip) {
  		printf("%s: cipher %s registered with a different template\n",
  			__func__, cip->ic_name);
  		return;
  	}
  	ciphers[cip->ic_cipher] = cip;
  }
  EXPORT_SYMBOL(ieee80211_crypto_register);
  
  /*
   * Unregister a crypto cipher module.
   */
  void
  ieee80211_crypto_unregister(const struct ieee80211_cipher *cip)
  {
  	if (cip->ic_cipher >= IEEE80211_CIPHER_MAX) {
  		printf("%s: cipher %s has an invalid cipher index %u\n",
  			__func__, cip->ic_name, cip->ic_cipher);
  		return;
  	}
  	if (ciphers[cip->ic_cipher] != NULL && ciphers[cip->ic_cipher] != cip) {
  		printf("%s: cipher %s registered with a different template\n",
  			__func__, cip->ic_name);
  		return;
  	}
  	/* NB: don't complain about not being registered */
  	/* XXX disallow if references */
  	ciphers[cip->ic_cipher] = NULL;
  }
  EXPORT_SYMBOL(ieee80211_crypto_unregister);
  
  int
  ieee80211_crypto_available(u_int cipher)
  {
  	return cipher < IEEE80211_CIPHER_MAX && ciphers[cipher] != NULL;
  }
  EXPORT_SYMBOL(ieee80211_crypto_available);
  
  /* XXX well-known names! */
  static const char *cipher_modnames[] = {
  	"wlan_wep",	/* IEEE80211_CIPHER_WEP */
  	"wlan_tkip",	/* IEEE80211_CIPHER_TKIP */
  	"wlan_aes_ocb",	/* IEEE80211_CIPHER_AES_OCB */
  	"wlan_ccmp",	/* IEEE80211_CIPHER_AES_CCM */
  	"wlan_ckip",	/* IEEE80211_CIPHER_CKIP */
  };
  
  /*
   * Establish a relationship between the specified key and cipher
   * and, if necessary, allocate a hardware index from the driver.
   * Note that when a fixed key index is required it must be specified
   * and we blindly assign it w/o consulting the driver (XXX).
   *
   * This must be the first call applied to a key; all the other key
   * routines assume wk_cipher is setup.
   *
   * Locking must be handled by the caller using:
   *	ieee80211_key_update_begin(vap);
   *	ieee80211_key_update_end(vap);
   */
  int
  ieee80211_crypto_newkey(struct ieee80211vap *vap,
  	int cipher, int flags, struct ieee80211_key *key)
  {
  #define	N(a)	(sizeof(a) / sizeof(a[0]))
  	const struct ieee80211_cipher *cip;
  	void *keyctx;
  	int oflags;
  
  	/*
  	 * Validate cipher and set reference to cipher routines.
  	 */
  	if (cipher >= IEEE80211_CIPHER_MAX) {
  		IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  			"%s: invalid cipher %u\n", __func__, cipher);
  		vap->iv_stats.is_crypto_badcipher++;
  		return 0;
  	}
  	cip = ciphers[cipher];
  	if (cip == NULL) {
  		/*
  		 * Auto-load cipher module if we have a well-known name
  		 * for it.  It might be better to use string names rather
  		 * than numbers and craft a module name based on the cipher
  		 * name; e.g. wlan_cipher_<cipher-name>.
  		 */
  		if (cipher < N(cipher_modnames)) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: unregistered cipher %u, load module %s\n",
  				__func__, cipher, cipher_modnames[cipher]);
  			ieee80211_load_module(cipher_modnames[cipher]);
  			/*
  			 * If cipher module loaded it should immediately
  			 * call ieee80211_crypto_register which will fill
  			 * in the entry in the ciphers array.
  			 */
  			cip = ciphers[cipher];
  		}
  		if (cip == NULL) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: unable to load cipher %u, module %s\n",
  				__func__, cipher,
  				cipher < N(cipher_modnames) ?
  					cipher_modnames[cipher] : "<unknown>");
  			vap->iv_stats.is_crypto_nocipher++;
  			return 0;
  		}
  	}
  
  	oflags = key->wk_flags;
  	flags &= IEEE80211_KEY_COMMON;
  	/*
  	 * If the hardware does not support the cipher then
  	 * fallback to a host-based implementation.
  	 */
  	if ((vap->iv_caps & (1<<cipher)) == 0) {
  		IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  		    "%s: no h/w support for cipher %s, falling back to s/w\n",
  		    __func__, cip->ic_name);
  		flags |= IEEE80211_KEY_SWCRYPT;
  	}
  	/*
  	 * Hardware TKIP with software MIC is an important
  	 * combination; we handle it by flagging each key,
  	 * the cipher modules honor it.
  	 */
  	if (cipher == IEEE80211_CIPHER_TKIP) {
  		if ((vap->iv_caps & IEEE80211_C_TKIPMIC) == 0) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: no h/w support for TKIP MIC, falling back to s/w\n",
  				__func__);        
  			flags |= IEEE80211_KEY_SWMIC;
          	} else if (((vap->iv_caps & IEEE80211_C_WME_TKIPMIC) == 0) &&
  		    (vap->iv_flags & IEEE80211_F_WME)) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: no h/w support for TKIP MIC when WMM is turned on,"
  				" falling back to s/w\n",
  				__func__);
  			flags |= IEEE80211_KEY_SWMIC;            
  		}
  	}
  
  	/*
  	 * Bind cipher to key instance.  Note we do this
  	 * after checking the device capabilities so the
  	 * cipher module can optimize space usage based on
  	 * whether or not it needs to do the cipher work.
  	 */
  	if (key->wk_cipher != cip || key->wk_flags != flags) {
  again:
  		/*
  		 * Fill in the flags so cipher modules can see s/w
  		 * crypto requirements and potentially allocate
  		 * different state and/or attach different method
  		 * pointers.
  		 *
  		 * XXX this is not right when s/w crypto fallback
  		 *     fails and we try to restore previous state.
  		 */
  		key->wk_flags = flags;
  		keyctx = cip->ic_attach(vap, key);
  		if (keyctx == NULL) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: unable to attach cipher %s\n",
  				__func__, cip->ic_name);
  			key->wk_flags = oflags;	/* restore old flags */
  			vap->iv_stats.is_crypto_attachfail++;
  			return 0;
  		}
  		cipher_detach(key);
  		key->wk_cipher = cip;		/* XXX refcnt? */
  		key->wk_private = keyctx;
  	}
  	/*
  	 * Commit to requested usage so driver can see the flags.
  	 */
  	key->wk_flags = flags;
  
  	/*
  	 * Ask the driver for a key index if we don't have one.
  	 * Note that entries in the global key table always have
  	 * an index; this means it's safe to call this routine
  	 * for these entries just to setup the reference to the
  	 * cipher template.  Note also that when using software
  	 * crypto we also call the driver to give us a key index.
  	 */
  	if (key->wk_keyix == IEEE80211_KEYIX_NONE) {
  		key->wk_keyix = dev_key_alloc(vap, key);
  		if (key->wk_keyix == IEEE80211_KEYIX_NONE) {
  			/*
  			 * Driver has no room; fallback to doing crypto
  			 * in the host.  We change the flags and start the
  			 * procedure over.  If we get back here then there's
  			 * no hope and we bail.  Note that this can leave
  			 * the key in a inconsistent state if the caller
  			 * continues to use it.
  			 */
  			if ((key->wk_flags & IEEE80211_KEY_SWCRYPT) == 0) {
  				vap->iv_stats.is_crypto_swfallback++;
  				IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  					"%s: no h/w resources for cipher %s, "
  					"falling back to s/w\n",
  					__func__, cip->ic_name);
  				oflags = key->wk_flags;
  				flags |= IEEE80211_KEY_SWCRYPT;
  				if (cipher == IEEE80211_CIPHER_TKIP)
  					flags |= IEEE80211_KEY_SWMIC;
  				goto again;
  			}
  			vap->iv_stats.is_crypto_keyfail++;
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: unable to setup cipher %s\n",
  				__func__, cip->ic_name);
  			return 0;
  		}
  	}
  	return 1;
  #undef N
  }
  EXPORT_SYMBOL(ieee80211_crypto_newkey);
  
  /*
   * Remove the key (no locking, for internal use).
   */
  static int
  _ieee80211_crypto_delkey(struct ieee80211vap *vap, struct ieee80211_key *key,
  	struct ieee80211_node *ni)
  {
  	u_int16_t keyix;
  
  	KASSERT(key->wk_cipher != NULL, ("No cipher!"));
  
  	IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  		"%s: %s keyix %u flags 0x%x tsc %llu len %u\n",
  		__func__, key->wk_cipher->ic_name,
  		key->wk_keyix, key->wk_flags,
  		key->wk_keytsc, key->wk_keylen);
  
  	keyix = key->wk_keyix;
  	if (keyix != IEEE80211_KEYIX_NONE) {
  		/*
  		 * Remove hardware entry.
  		 */
  		/* XXX key cache */
  		if (!dev_key_delete(vap, key, ni)) {
  			IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  				"%s: driver did not delete key index %u\n",
  				__func__, keyix);
  			vap->iv_stats.is_crypto_delkey++;
  			/* XXX recovery? */
  		}
  	}
  	cipher_detach(key);
  	memset(key, 0, sizeof(*key));
  	ieee80211_crypto_resetkey(vap, key, IEEE80211_KEYIX_NONE);
  	return 1;
  }
  
  /*
   * Remove the specified key.
   */
  int
  ieee80211_crypto_delkey(struct ieee80211vap *vap, struct ieee80211_key *key, 
  	struct ieee80211_node *ni)
  {
  	int status;
  
  #ifdef ATH_SUPERG_COMP
  	/* if valid node entry is present cleanup the compression state */
  	if (ni)
  		dev_comp_set(vap, ni, 0);
  #endif
  	ieee80211_key_update_begin(vap);
  	status = _ieee80211_crypto_delkey(vap, key, ni);
  	ieee80211_key_update_end(vap);
  
  	return status;
  }
  EXPORT_SYMBOL(ieee80211_crypto_delkey);
  
  /*
   * Clear the global key table.
   */
  void
  ieee80211_crypto_delglobalkeys(struct ieee80211vap *vap)
  {
  	int i;
  
  	ieee80211_key_update_begin(vap);
  	for (i = 0; i < IEEE80211_WEP_NKID; i++)
  		(void) _ieee80211_crypto_delkey(vap, &vap->iv_nw_keys[i], NULL);
  	ieee80211_key_update_end(vap);
  }
  EXPORT_SYMBOL(ieee80211_crypto_delglobalkeys);
  
  /*
   * Set the contents of the specified key.
   *
   * Locking must be handled by the caller using:
   *	ieee80211_key_update_begin(vap);
   *	ieee80211_key_update_end(vap);
   */
  int
  ieee80211_crypto_setkey(struct ieee80211vap *vap, struct ieee80211_key *key,
  	const u_int8_t macaddr[IEEE80211_ADDR_LEN],
  	struct ieee80211_node *ni)
  {
  	const struct ieee80211_cipher *cip = key->wk_cipher;
  	int ret;
  
  	KASSERT(cip != NULL, ("No cipher!"));
  
  	IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  		"%s: %s keyix %u flags 0x%x mac %s  tsc %llu len %u\n",
  		__func__, cip->ic_name, key->wk_keyix,
  		key->wk_flags, ether_sprintf(macaddr),
  		key->wk_keytsc, key->wk_keylen);
  
  	/*
  	 * Give cipher a chance to validate key contents.
  	 * XXX should happen before modifying state.
  	 */
  	if (!cip->ic_setkey(key)) {
  		IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  			"%s: cipher %s rejected key index %u len %u flags 0x%x\n",
  			__func__, cip->ic_name, key->wk_keyix,
  			key->wk_keylen, key->wk_flags);
  		vap->iv_stats.is_crypto_setkey_cipher++;
  		return 0;
  	}
  	if (key->wk_keyix == IEEE80211_KEYIX_NONE) {
  		/* XXX nothing allocated, should not happen */
  		IEEE80211_DPRINTF(vap, IEEE80211_MSG_CRYPTO,
  			"%s: no key index; should not happen!\n", __func__);
  		vap->iv_stats.is_crypto_setkey_nokey++;
  		return 0;
  	}
  	ret = dev_key_set(vap, key, macaddr);
  #ifdef ATH_SUPERG_COMP
  	if (ret && ni) {
                 /* Enable decompression only receive key entries */
                  if (key->wk_flags & IEEE80211_KEY_RECV)
  			dev_comp_set(vap, ni, 1);
  	}
  #endif
  
  	return ret;
  }
  EXPORT_SYMBOL(ieee80211_crypto_setkey);
  
  /*
   * Add privacy headers appropriate for the specified key.
   */
  struct ieee80211_key *
  ieee80211_crypto_encap(struct ieee80211_node *ni, struct sk_buff *skb)
  {
  	struct ieee80211vap *vap = ni->ni_vap;
  	struct ieee80211_key *k;
  	struct ieee80211_frame *wh;
  	const struct ieee80211_cipher *cip;
  	u_int8_t keyid;
  
  	/*
  	 * Multicast traffic always uses the multicast key.
  	 * Otherwise if a unicast key is set we use that and
  	 * it is always key index 0.  When no unicast key is
  	 * set we fall back to the default transmit key.
  	 */
  	wh = (struct ieee80211_frame *)skb->data;
  	if (IEEE80211_IS_MULTICAST(wh->i_addr1) ||
  	    ni->ni_ucastkey.wk_cipher == &ieee80211_cipher_none) {
  		if (vap->iv_def_txkey == IEEE80211_KEYIX_NONE) {
  			IEEE80211_NOTE_MAC(vap, IEEE80211_MSG_CRYPTO,
  				wh->i_addr1,
  				"no default transmit key (%s) deftxkey %u",
  				__func__, vap->iv_def_txkey);
  			vap->iv_stats.is_tx_nodefkey++;
  			return NULL;
  		}
  		keyid = vap->iv_def_txkey;
  		k = &vap->iv_nw_keys[vap->iv_def_txkey];
  	} else {
  		keyid = 0;
  		k = &ni->ni_ucastkey;
  	}
  	cip = k->wk_cipher;
  	if (skb_headroom(skb) < cip->ic_header) {
  		/*
  		 * Should not happen; ieee80211_skbhdr_adjust should
  		 * have allocated enough space for all headers.
  		 */
  		IEEE80211_NOTE_MAC(vap, IEEE80211_MSG_CRYPTO, wh->i_addr1,
  			"%s: malformed packet for cipher %s; headroom %u",
  			__func__, cip->ic_name, skb_headroom(skb));
  		vap->iv_stats.is_tx_noheadroom++;
  		return NULL;
  	}
  	return (cip->ic_encap(k, skb, keyid << 6) ? k : NULL);
  }
  EXPORT_SYMBOL(ieee80211_crypto_encap);
  
  /*
   * Validate and strip privacy headers (and trailer) for a
   * received frame that has the Protected Frame bit set.
   */
  struct ieee80211_key *
  ieee80211_crypto_decap(struct ieee80211_node *ni, struct sk_buff *skb, int hdrlen)
  {
  #define	IEEE80211_WEP_HDRLEN	(IEEE80211_WEP_IVLEN + IEEE80211_WEP_KIDLEN)
  #define	IEEE80211_WEP_MINLEN \
  	(sizeof(struct ieee80211_frame) + \
  	IEEE80211_WEP_HDRLEN + IEEE80211_WEP_CRCLEN)
  	struct ieee80211vap *vap = ni->ni_vap;
  	struct ieee80211_key *k;
  	struct ieee80211_frame *wh;
  	const struct ieee80211_cipher *cip;
  	const u_int8_t *ivp;
  	u_int8_t keyid;
  
  	/* NB: this minimum size data frame could be bigger */
  	if (skb->len < IEEE80211_WEP_MINLEN) {
  		IEEE80211_NOTE(vap, IEEE80211_MSG_ANY, ni,
  			"%s: WEP data frame too short, len %u",
  			__func__, skb->len);
  		vap->iv_stats.is_rx_tooshort++;	/* XXX need unique stat? */
  		return NULL;
  	}
  	/*
  	 * Locate the key. If unicast and there is no unicast
  	 * key then we fall back to the key id in the header.
  	 * This assumes unicast keys are only configured when
  	 * the key id in the header is meaningless (typically 0).
  	 */
  	wh = (struct ieee80211_frame *) skb->data;
  	ivp = skb->data + hdrlen;
  	keyid = ivp[IEEE80211_WEP_IVLEN];
  	if (IEEE80211_IS_MULTICAST(wh->i_addr1) ||
  	    ni->ni_ucastkey.wk_cipher == &ieee80211_cipher_none)
  		k = &vap->iv_nw_keys[keyid >> 6];
  	else
  		k = &ni->ni_ucastkey;
  
  	cip = k->wk_cipher;
  	return (cip->ic_decap(k, skb, hdrlen) ? k : NULL);
  #undef IEEE80211_WEP_MINLEN
  #undef IEEE80211_WEP_HDRLEN
  }
  EXPORT_SYMBOL(ieee80211_crypto_decap);
  