net/mac80211/wpa.c

   1 /*
   2  * Copyright 2002-2004, Instant802 Networks, Inc.
   3  * Copyright 2008, Jouni Malinen <j@w1.fi>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9
  10 #include <linux/netdevice.h>
  11 #include <linux/types.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/compiler.h>
  14 #include <linux/ieee80211.h>
  15 #include <linux/gfp.h>
  16 #include <asm/unaligned.h>
  17 #include <net/mac80211.h>
  18
  19 #include "ieee80211_i.h"
  20 #include "michael.h"
  21 #include "tkip.h"
  22 #include "aes_ccm.h"
  23 #include "aes_cmac.h"
  24 #include "wpa.h"
  25
  26 ieee80211_tx_result
  27 ieee80211_tx_h_michael_mic_add(struct ieee80211_tx_data *tx)
  28 {
  29         u8 *data, *key, *mic;
  30         size_t data_len;
  31         unsigned int hdrlen;
  32         struct ieee80211_hdr *hdr;
  33         struct sk_buff *skb = tx->skb;
  34         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
  35         int tail;
  36
  37         hdr = (struct ieee80211_hdr *)skb->data;
  38         if (!tx->key || tx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
  39             skb->len < 24 || !ieee80211_is_data_present(hdr->frame_control))
  40                 return TX_CONTINUE;
  41
  42         hdrlen = ieee80211_hdrlen(hdr->frame_control);
  43         if (skb->len < hdrlen)
  44                 return TX_DROP;
  45
  46         data = skb->data + hdrlen;
  47         data_len = skb->len - hdrlen;
  48
  49         if (unlikely(info->flags & IEEE80211_TX_INTFL_TKIP_MIC_FAILURE)) {
  50                 /* Need to use software crypto for the test */
  51                 info->control.hw_key = NULL;
  52         }
  53
  54         if (info->control.hw_key &&
  55             !(tx->flags & IEEE80211_TX_FRAGMENTED) &&
  56             !(tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC)) {
  57                 /* hwaccel - with no need for SW-generated MMIC */
  58                 return TX_CONTINUE;
  59         }
  60
  61         tail = MICHAEL_MIC_LEN;
  62         if (!info->control.hw_key)
  63                 tail += TKIP_ICV_LEN;
  64
  65         if (WARN_ON(skb_tailroom(skb) < tail ||
  66                     skb_headroom(skb) < TKIP_IV_LEN))
  67                 return TX_DROP;
  68
  69         key = &tx->key->conf.key[NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY];
  70         mic = skb_put(skb, MICHAEL_MIC_LEN);
  71         michael_mic(key, hdr, data, data_len, mic);
  72         if (unlikely(info->flags & IEEE80211_TX_INTFL_TKIP_MIC_FAILURE))
  73                 mic[0]++;
  74
  75         return TX_CONTINUE;
  76 }
  77
  78
  79 ieee80211_rx_result
  80 ieee80211_rx_h_michael_mic_verify(struct ieee80211_rx_data *rx)
  81 {
  82         u8 *data, *key = NULL;
  83         size_t data_len;
  84         unsigned int hdrlen;
  85         u8 mic[MICHAEL_MIC_LEN];
  86         struct sk_buff *skb = rx->skb;
  87         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
  88         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  89
  90         /* No way to verify the MIC if the hardware stripped it */
  91         if (status->flag & RX_FLAG_MMIC_STRIPPED)
  92                 return RX_CONTINUE;
  93
  94         if (!rx->key || rx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
  95             !ieee80211_has_protected(hdr->frame_control) ||
  96             !ieee80211_is_data_present(hdr->frame_control))
  97                 return RX_CONTINUE;
  98
  99         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 100         if (skb->len < hdrlen + MICHAEL_MIC_LEN)
 101                 return RX_DROP_UNUSABLE;
 102
 103         data = skb->data + hdrlen;
 104         data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
 105
 106         key = &rx->key->conf.key[NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY];
 107         michael_mic(key, hdr, data, data_len, mic);
 108         if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0) {
 109                 if (!(status->rx_flags & IEEE80211_RX_RA_MATCH))
 110                         return RX_DROP_UNUSABLE;
 111
 112                 mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
 113                                                 (void *) skb->data, NULL,
 114                                                 GFP_ATOMIC);
 115                 return RX_DROP_UNUSABLE;
 116         }
 117
 118         /* remove Michael MIC from payload */
 119         skb_trim(skb, skb->len - MICHAEL_MIC_LEN);
 120
 121         /* update IV in key information to be able to detect replays */
 122         rx->key->u.tkip.rx[rx->queue].iv32 = rx->tkip_iv32;
 123         rx->key->u.tkip.rx[rx->queue].iv16 = rx->tkip_iv16;
 124
 125         return RX_CONTINUE;
 126 }
 127
 128
 129 static int tkip_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 130 {
 131         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 132         struct ieee80211_key *key = tx->key;
 133         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 134         unsigned int hdrlen;
 135         int len, tail;
 136         u8 *pos;
 137
 138         if (info->control.hw_key &&
 139             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 140                 /* hwaccel - with no need for software-generated IV */
 141                 return 0;
 142         }
 143
 144         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 145         len = skb->len - hdrlen;
 146
 147         if (info->control.hw_key)
 148                 tail = 0;
 149         else
 150                 tail = TKIP_ICV_LEN;
 151
 152         if (WARN_ON(skb_tailroom(skb) < tail ||
 153                     skb_headroom(skb) < TKIP_IV_LEN))
 154                 return -1;
 155
 156         pos = skb_push(skb, TKIP_IV_LEN);
 157         memmove(pos, pos + TKIP_IV_LEN, hdrlen);
 158         pos += hdrlen;
 159
 160         /* Increase IV for the frame */
 161         key->u.tkip.tx.iv16++;
 162         if (key->u.tkip.tx.iv16 == 0)
 163                 key->u.tkip.tx.iv32++;
 164
 165         pos = ieee80211_tkip_add_iv(pos, key, key->u.tkip.tx.iv16);
 166
 167         /* hwaccel - with software IV */
 168         if (info->control.hw_key)
 169                 return 0;
 170
 171         /* Add room for ICV */
 172         skb_put(skb, TKIP_ICV_LEN);
 173
 174         hdr = (struct ieee80211_hdr *) skb->data;
 175         return ieee80211_tkip_encrypt_data(tx->local->wep_tx_tfm,
 176                                            key, pos, len, hdr->addr2);
 177 }
 178
 179
 180 ieee80211_tx_result
 181 ieee80211_crypto_tkip_encrypt(struct ieee80211_tx_data *tx)
 182 {
 183         struct sk_buff *skb = tx->skb;
 184
 185         ieee80211_tx_set_protected(tx);
 186
 187         do {
 188                 if (tkip_encrypt_skb(tx, skb) < 0)
 189                         return TX_DROP;
 190         } while ((skb = skb->next));
 191
 192         return TX_CONTINUE;
 193 }
 194
 195
 196 ieee80211_rx_result
 197 ieee80211_crypto_tkip_decrypt(struct ieee80211_rx_data *rx)
 198 {
 199         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
 200         int hdrlen, res, hwaccel = 0;
 201         struct ieee80211_key *key = rx->key;
 202         struct sk_buff *skb = rx->skb;
 203         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 204
 205         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 206
 207         if (!ieee80211_is_data(hdr->frame_control))
 208                 return RX_CONTINUE;
 209
 210         if (!rx->sta || skb->len - hdrlen < 12)
 211                 return RX_DROP_UNUSABLE;
 212
 213         /*
 214          * Let TKIP code verify IV, but skip decryption.
 215          * In the case where hardware checks the IV as well,
 216          * we don't even get here, see ieee80211_rx_h_decrypt()
 217          */
 218         if (status->flag & RX_FLAG_DECRYPTED)
 219                 hwaccel = 1;
 220
 221         res = ieee80211_tkip_decrypt_data(rx->local->wep_rx_tfm,
 222                                           key, skb->data + hdrlen,
 223                                           skb->len - hdrlen, rx->sta->sta.addr,
 224                                           hdr->addr1, hwaccel, rx->queue,
 225                                           &rx->tkip_iv32,
 226                                           &rx->tkip_iv16);
 227         if (res != TKIP_DECRYPT_OK)
 228                 return RX_DROP_UNUSABLE;
 229
 230         /* Trim ICV */
 231         skb_trim(skb, skb->len - TKIP_ICV_LEN);
 232
 233         /* Remove IV */
 234         memmove(skb->data + TKIP_IV_LEN, skb->data, hdrlen);
 235         skb_pull(skb, TKIP_IV_LEN);
 236
 237         return RX_CONTINUE;
 238 }
 239
 240
 241 static void ccmp_special_blocks(struct sk_buff *skb, u8 *pn, u8 *scratch,
 242                                 int encrypted)
 243 {
 244         __le16 mask_fc;
 245         int a4_included, mgmt;
 246         u8 qos_tid;
 247         u8 *b_0, *aad;
 248         u16 data_len, len_a;
 249         unsigned int hdrlen;
 250         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 251
 252         b_0 = scratch + 3 * AES_BLOCK_LEN;
 253         aad = scratch + 4 * AES_BLOCK_LEN;
 254
 255         /*
 256          * Mask FC: zero subtype b4 b5 b6 (if not mgmt)
 257          * Retry, PwrMgt, MoreData; set Protected
 258          */
 259         mgmt = ieee80211_is_mgmt(hdr->frame_control);
 260         mask_fc = hdr->frame_control;
 261         mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY |
 262                                 IEEE80211_FCTL_PM | IEEE80211_FCTL_MOREDATA);
 263         if (!mgmt)
 264                 mask_fc &= ~cpu_to_le16(0x0070);
 265         mask_fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 266
 267         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 268         len_a = hdrlen - 2;
 269         a4_included = ieee80211_has_a4(hdr->frame_control);
 270
 271         if (ieee80211_is_data_qos(hdr->frame_control))
 272                 qos_tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
 273         else
 274                 qos_tid = 0;
 275
 276         data_len = skb->len - hdrlen - CCMP_HDR_LEN;
 277         if (encrypted)
 278                 data_len -= CCMP_MIC_LEN;
 279
 280         /* First block, b_0 */
 281         b_0[0] = 0x59; /* flags: Adata: 1, M: 011, L: 001 */
 282         /* Nonce: Nonce Flags | A2 | PN
 283          * Nonce Flags: Priority (b0..b3) | Management (b4) | Reserved (b5..b7)
 284          */
 285         b_0[1] = qos_tid | (mgmt << 4);
 286         memcpy(&b_0[2], hdr->addr2, ETH_ALEN);
 287         memcpy(&b_0[8], pn, CCMP_PN_LEN);
 288         /* l(m) */
 289         put_unaligned_be16(data_len, &b_0[14]);
 290
 291         /* AAD (extra authenticate-only data) / masked 802.11 header
 292          * FC | A1 | A2 | A3 | SC | [A4] | [QC] */
 293         put_unaligned_be16(len_a, &aad[0]);
 294         put_unaligned(mask_fc, (__le16 *)&aad[2]);
 295         memcpy(&aad[4], &hdr->addr1, 3 * ETH_ALEN);
 296
 297         /* Mask Seq#, leave Frag# */
 298         aad[22] = *((u8 *) &hdr->seq_ctrl) & 0x0f;
 299         aad[23] = 0;
 300
 301         if (a4_included) {
 302                 memcpy(&aad[24], hdr->addr4, ETH_ALEN);
 303                 aad[30] = qos_tid;
 304                 aad[31] = 0;
 305         } else {
 306                 memset(&aad[24], 0, ETH_ALEN + IEEE80211_QOS_CTL_LEN);
 307                 aad[24] = qos_tid;
 308         }
 309 }
 310
 311
 312 static inline void ccmp_pn2hdr(u8 *hdr, u8 *pn, int key_id)
 313 {
 314         hdr[0] = pn[5];
 315         hdr[1] = pn[4];
 316         hdr[2] = 0;
 317         hdr[3] = 0x20 | (key_id << 6);
 318         hdr[4] = pn[3];
 319         hdr[5] = pn[2];
 320         hdr[6] = pn[1];
 321         hdr[7] = pn[0];
 322 }
 323
 324
 325 static inline void ccmp_hdr2pn(u8 *pn, u8 *hdr)
 326 {
 327         pn[0] = hdr[7];
 328         pn[1] = hdr[6];
 329         pn[2] = hdr[5];
 330         pn[3] = hdr[4];
 331         pn[4] = hdr[1];
 332         pn[5] = hdr[0];
 333 }
 334
 335
 336 static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 337 {
 338         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 339         struct ieee80211_key *key = tx->key;
 340         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 341         int hdrlen, len, tail;
 342         u8 *pos, *pn;
 343         int i;
 344
 345         if (info->control.hw_key &&
 346             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 347                 /*
 348                  * hwaccel has no need for preallocated room for CCMP
 349                  * header or MIC fields
 350                  */
 351                 return 0;
 352         }
 353
 354         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 355         len = skb->len - hdrlen;
 356
 357         if (info->control.hw_key)
 358                 tail = 0;
 359         else
 360                 tail = CCMP_MIC_LEN;
 361
 362         if (WARN_ON(skb_tailroom(skb) < tail ||
 363                     skb_headroom(skb) < CCMP_HDR_LEN))
 364                 return -1;
 365
 366         pos = skb_push(skb, CCMP_HDR_LEN);
 367         memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
 368         hdr = (struct ieee80211_hdr *) pos;
 369         pos += hdrlen;
 370
 371         /* PN = PN + 1 */
 372         pn = key->u.ccmp.tx_pn;
 373
 374         for (i = CCMP_PN_LEN - 1; i >= 0; i--) {
 375                 pn[i]++;
 376                 if (pn[i])
 377                         break;
 378         }
 379
 380         ccmp_pn2hdr(pos, pn, key->conf.keyidx);
 381
 382         /* hwaccel - with software CCMP header */
 383         if (info->control.hw_key)
 384                 return 0;
 385
 386         pos += CCMP_HDR_LEN;
 387         ccmp_special_blocks(skb, pn, key->u.ccmp.tx_crypto_buf, 0);
 388         ieee80211_aes_ccm_encrypt(key->u.ccmp.tfm, key->u.ccmp.tx_crypto_buf, pos, len,
 389                                   pos, skb_put(skb, CCMP_MIC_LEN));
 390
 391         return 0;
 392 }
 393
 394
 395 ieee80211_tx_result
 396 ieee80211_crypto_ccmp_encrypt(struct ieee80211_tx_data *tx)
 397 {
 398         struct sk_buff *skb = tx->skb;
 399
 400         ieee80211_tx_set_protected(tx);
 401
 402         do {
 403                 if (ccmp_encrypt_skb(tx, skb) < 0)
 404                         return TX_DROP;
 405         } while ((skb = skb->next));
 406
 407         return TX_CONTINUE;
 408 }
 409
 410
 411 ieee80211_rx_result
 412 ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
 413 {
 414         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 415         int hdrlen;
 416         struct ieee80211_key *key = rx->key;
 417         struct sk_buff *skb = rx->skb;
 418         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 419         u8 pn[CCMP_PN_LEN];
 420         int data_len;
 421         int queue;
 422
 423         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 424
 425         if (!ieee80211_is_data(hdr->frame_control) &&
 426             !ieee80211_is_robust_mgmt_frame(hdr))
 427                 return RX_CONTINUE;
 428
 429         data_len = skb->len - hdrlen - CCMP_HDR_LEN - CCMP_MIC_LEN;
 430         if (!rx->sta || data_len < 0)
 431                 return RX_DROP_UNUSABLE;
 432
 433         ccmp_hdr2pn(pn, skb->data + hdrlen);
 434
 435         queue = ieee80211_is_mgmt(hdr->frame_control) ?
 436                 NUM_RX_DATA_QUEUES : rx->queue;
 437
 438         if (memcmp(pn, key->u.ccmp.rx_pn[queue], CCMP_PN_LEN) <= 0) {
 439                 key->u.ccmp.replays++;
 440                 return RX_DROP_UNUSABLE;
 441         }
 442
 443         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 444                 /* hardware didn't decrypt/verify MIC */
 445                 ccmp_special_blocks(skb, pn, key->u.ccmp.rx_crypto_buf, 1);
 446
 447                 if (ieee80211_aes_ccm_decrypt(
 448                             key->u.ccmp.tfm, key->u.ccmp.rx_crypto_buf,
 449                             skb->data + hdrlen + CCMP_HDR_LEN, data_len,
 450                             skb->data + skb->len - CCMP_MIC_LEN,
 451                             skb->data + hdrlen + CCMP_HDR_LEN))
 452                         return RX_DROP_UNUSABLE;
 453         }
 454
 455         memcpy(key->u.ccmp.rx_pn[queue], pn, CCMP_PN_LEN);
 456
 457         /* Remove CCMP header and MIC */
 458         skb_trim(skb, skb->len - CCMP_MIC_LEN);
 459         memmove(skb->data + CCMP_HDR_LEN, skb->data, hdrlen);
 460         skb_pull(skb, CCMP_HDR_LEN);
 461
 462         return RX_CONTINUE;
 463 }
 464
 465
 466 static void bip_aad(struct sk_buff *skb, u8 *aad)
 467 {
 468         /* BIP AAD: FC(masked) || A1 || A2 || A3 */
 469
 470         /* FC type/subtype */
 471         aad[0] = skb->data[0];
 472         /* Mask FC Retry, PwrMgt, MoreData flags to zero */
 473         aad[1] = skb->data[1] & ~(BIT(4) | BIT(5) | BIT(6));
 474         /* A1 || A2 || A3 */
 475         memcpy(aad + 2, skb->data + 4, 3 * ETH_ALEN);
 476 }
 477
 478
 479 static inline void bip_ipn_swap(u8 *d, const u8 *s)
 480 {
 481         *d++ = s[5];
 482         *d++ = s[4];
 483         *d++ = s[3];
 484         *d++ = s[2];
 485         *d++ = s[1];
 486         *d = s[0];
 487 }
 488
 489
 490 ieee80211_tx_result
 491 ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
 492 {
 493         struct sk_buff *skb = tx->skb;
 494         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 495         struct ieee80211_key *key = tx->key;
 496         struct ieee80211_mmie *mmie;
 497         u8 *pn, aad[20];
 498         int i;
 499
 500         if (info->control.hw_key)
 501                 return 0;
 502
 503         if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
 504                 return TX_DROP;
 505
 506         mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
 507         mmie->element_id = WLAN_EID_MMIE;
 508         mmie->length = sizeof(*mmie) - 2;
 509         mmie->key_id = cpu_to_le16(key->conf.keyidx);
 510
 511         /* PN = PN + 1 */
 512         pn = key->u.aes_cmac.tx_pn;
 513
 514         for (i = sizeof(key->u.aes_cmac.tx_pn) - 1; i >= 0; i--) {
 515                 pn[i]++;
 516                 if (pn[i])
 517                         break;
 518         }
 519         bip_ipn_swap(mmie->sequence_number, pn);
 520
 521         bip_aad(skb, aad);
 522
 523         /*
 524          * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
 525          */
 526         ieee80211_aes_cmac(key->u.aes_cmac.tfm, key->u.aes_cmac.tx_crypto_buf,
 527                            aad, skb->data + 24, skb->len - 24, mmie->mic);
 528
 529         return TX_CONTINUE;
 530 }
 531
 532
 533 ieee80211_rx_result
 534 ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 535 {
 536         struct sk_buff *skb = rx->skb;
 537         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 538         struct ieee80211_key *key = rx->key;
 539         struct ieee80211_mmie *mmie;
 540         u8 aad[20], mic[8], ipn[6];
 541         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 542
 543         if (!ieee80211_is_mgmt(hdr->frame_control))
 544                 return RX_CONTINUE;
 545
 546         if (skb->len < 24 + sizeof(*mmie))
 547                 return RX_DROP_UNUSABLE;
 548
 549         mmie = (struct ieee80211_mmie *)
 550                 (skb->data + skb->len - sizeof(*mmie));
 551         if (mmie->element_id != WLAN_EID_MMIE ||
 552             mmie->length != sizeof(*mmie) - 2)
 553                 return RX_DROP_UNUSABLE; /* Invalid MMIE */
 554
 555         bip_ipn_swap(ipn, mmie->sequence_number);
 556
 557         if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 558                 key->u.aes_cmac.replays++;
 559                 return RX_DROP_UNUSABLE;
 560         }
 561
 562         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 563                 /* hardware didn't decrypt/verify MIC */
 564                 bip_aad(skb, aad);
 565                 ieee80211_aes_cmac(key->u.aes_cmac.tfm,
 566                                    key->u.aes_cmac.rx_crypto_buf, aad,
 567                                    skb->data + 24, skb->len - 24, mic);
 568                 if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
 569                         key->u.aes_cmac.icverrors++;
 570                         return RX_DROP_UNUSABLE;
 571                 }
 572         }
 573
 574         memcpy(key->u.aes_cmac.rx_pn, ipn, 6);
 575
 576         /* Remove MMIE */
 577         skb_trim(skb, skb->len - sizeof(*mmie));
 578
 579         return RX_CONTINUE;
 580 }