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         /*
  91          * it makes no sense to check for MIC errors on anything other
  92          * than data frames.
  93          */
  94         if (!ieee80211_is_data_present(hdr->frame_control))
  95                 return RX_CONTINUE;
  96
  97         /*
  98          * No way to verify the MIC if the hardware stripped it or
  99          * the IV with the key index. In this case we have solely rely
 100          * on the driver to set RX_FLAG_MMIC_ERROR in the event of a
 101          * MIC failure report.
 102          */
 103         if (status->flag & (RX_FLAG_MMIC_STRIPPED | RX_FLAG_IV_STRIPPED)) {
 104                 if (status->flag & RX_FLAG_MMIC_ERROR)
 105                         goto mic_fail;
 106
 107                 if (!(status->flag & RX_FLAG_IV_STRIPPED))
 108                         goto update_iv;
 109
 110                 return RX_CONTINUE;
 111         }
 112
 113         /*
 114          * Some hardware seems to generate Michael MIC failure reports; even
 115          * though, the frame was not encrypted with TKIP and therefore has no
 116          * MIC. Ignore the flag them to avoid triggering countermeasures.
 117          */
 118         if (!rx->key || rx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
 119             !(status->flag & RX_FLAG_DECRYPTED))
 120                 return RX_CONTINUE;
 121
 122         if (rx->sdata->vif.type == NL80211_IFTYPE_AP && rx->key->conf.keyidx) {
 123                 /*
 124                  * APs with pairwise keys should never receive Michael MIC
 125                  * errors for non-zero keyidx because these are reserved for
 126                  * group keys and only the AP is sending real multicast
 127                  * frames in the BSS. (
 128                  */
 129                 return RX_DROP_UNUSABLE;
 130         }
 131
 132         if (status->flag & RX_FLAG_MMIC_ERROR)
 133                 goto mic_fail;
 134
 135         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 136         if (skb->len < hdrlen + MICHAEL_MIC_LEN)
 137                 return RX_DROP_UNUSABLE;
 138
 139         data = skb->data + hdrlen;
 140         data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
 141         key = &rx->key->conf.key[NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY];
 142         michael_mic(key, hdr, data, data_len, mic);
 143         if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0)
 144                 goto mic_fail;
 145
 146         /* remove Michael MIC from payload */
 147         skb_trim(skb, skb->len - MICHAEL_MIC_LEN);
 148
 149 update_iv:
 150         /* update IV in key information to be able to detect replays */
 151         rx->key->u.tkip.rx[rx->queue].iv32 = rx->tkip_iv32;
 152         rx->key->u.tkip.rx[rx->queue].iv16 = rx->tkip_iv16;
 153
 154         return RX_CONTINUE;
 155
 156 mic_fail:
 157         /*
 158          * In some cases the key can be unset - e.g. a multicast packet, in
 159          * a driver that supports HW encryption. Send up the key idx only if
 160          * the key is set.
 161          */
 162         mac80211_ev_michael_mic_failure(rx->sdata,
 163                                         rx->key ? rx->key->conf.keyidx : -1,
 164                                         (void *) skb->data, NULL, GFP_ATOMIC);
 165         return RX_DROP_UNUSABLE;
 166 }
 167
 168
 169 static int tkip_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 170 {
 171         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 172         struct ieee80211_key *key = tx->key;
 173         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 174         unsigned int hdrlen;
 175         int len, tail;
 176         u8 *pos;
 177
 178         if (info->control.hw_key &&
 179             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 180                 /* hwaccel - with no need for software-generated IV */
 181                 return 0;
 182         }
 183
 184         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 185         len = skb->len - hdrlen;
 186
 187         if (info->control.hw_key)
 188                 tail = 0;
 189         else
 190                 tail = TKIP_ICV_LEN;
 191
 192         if (WARN_ON(skb_tailroom(skb) < tail ||
 193                     skb_headroom(skb) < TKIP_IV_LEN))
 194                 return -1;
 195
 196         pos = skb_push(skb, TKIP_IV_LEN);
 197         memmove(pos, pos + TKIP_IV_LEN, hdrlen);
 198         pos += hdrlen;
 199
 200         /* Increase IV for the frame */
 201         key->u.tkip.tx.iv16++;
 202         if (key->u.tkip.tx.iv16 == 0)
 203                 key->u.tkip.tx.iv32++;
 204
 205         pos = ieee80211_tkip_add_iv(pos, key, key->u.tkip.tx.iv16);
 206
 207         /* hwaccel - with software IV */
 208         if (info->control.hw_key)
 209                 return 0;
 210
 211         /* Add room for ICV */
 212         skb_put(skb, TKIP_ICV_LEN);
 213
 214         hdr = (struct ieee80211_hdr *) skb->data;
 215         return ieee80211_tkip_encrypt_data(tx->local->wep_tx_tfm,
 216                                            key, pos, len, hdr->addr2);
 217 }
 218
 219
 220 ieee80211_tx_result
 221 ieee80211_crypto_tkip_encrypt(struct ieee80211_tx_data *tx)
 222 {
 223         struct sk_buff *skb = tx->skb;
 224
 225         ieee80211_tx_set_protected(tx);
 226
 227         do {
 228                 if (tkip_encrypt_skb(tx, skb) < 0)
 229                         return TX_DROP;
 230         } while ((skb = skb->next));
 231
 232         return TX_CONTINUE;
 233 }
 234
 235
 236 ieee80211_rx_result
 237 ieee80211_crypto_tkip_decrypt(struct ieee80211_rx_data *rx)
 238 {
 239         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
 240         int hdrlen, res, hwaccel = 0;
 241         struct ieee80211_key *key = rx->key;
 242         struct sk_buff *skb = rx->skb;
 243         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 244
 245         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 246
 247         if (!ieee80211_is_data(hdr->frame_control))
 248                 return RX_CONTINUE;
 249
 250         if (!rx->sta || skb->len - hdrlen < 12)
 251                 return RX_DROP_UNUSABLE;
 252
 253         /*
 254          * Let TKIP code verify IV, but skip decryption.
 255          * In the case where hardware checks the IV as well,
 256          * we don't even get here, see ieee80211_rx_h_decrypt()
 257          */
 258         if (status->flag & RX_FLAG_DECRYPTED)
 259                 hwaccel = 1;
 260
 261         res = ieee80211_tkip_decrypt_data(rx->local->wep_rx_tfm,
 262                                           key, skb->data + hdrlen,
 263                                           skb->len - hdrlen, rx->sta->sta.addr,
 264                                           hdr->addr1, hwaccel, rx->queue,
 265                                           &rx->tkip_iv32,
 266                                           &rx->tkip_iv16);
 267         if (res != TKIP_DECRYPT_OK)
 268                 return RX_DROP_UNUSABLE;
 269
 270         /* Trim ICV */
 271         skb_trim(skb, skb->len - TKIP_ICV_LEN);
 272
 273         /* Remove IV */
 274         memmove(skb->data + TKIP_IV_LEN, skb->data, hdrlen);
 275         skb_pull(skb, TKIP_IV_LEN);
 276
 277         return RX_CONTINUE;
 278 }
 279
 280
 281 static void ccmp_special_blocks(struct sk_buff *skb, u8 *pn, u8 *scratch,
 282                                 int encrypted)
 283 {
 284         __le16 mask_fc;
 285         int a4_included, mgmt;
 286         u8 qos_tid;
 287         u8 *b_0, *aad;
 288         u16 data_len, len_a;
 289         unsigned int hdrlen;
 290         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 291
 292         b_0 = scratch + 3 * AES_BLOCK_LEN;
 293         aad = scratch + 4 * AES_BLOCK_LEN;
 294
 295         /*
 296          * Mask FC: zero subtype b4 b5 b6 (if not mgmt)
 297          * Retry, PwrMgt, MoreData; set Protected
 298          */
 299         mgmt = ieee80211_is_mgmt(hdr->frame_control);
 300         mask_fc = hdr->frame_control;
 301         mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY |
 302                                 IEEE80211_FCTL_PM | IEEE80211_FCTL_MOREDATA);
 303         if (!mgmt)
 304                 mask_fc &= ~cpu_to_le16(0x0070);
 305         mask_fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 306
 307         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 308         len_a = hdrlen - 2;
 309         a4_included = ieee80211_has_a4(hdr->frame_control);
 310
 311         if (ieee80211_is_data_qos(hdr->frame_control))
 312                 qos_tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
 313         else
 314                 qos_tid = 0;
 315
 316         data_len = skb->len - hdrlen - CCMP_HDR_LEN;
 317         if (encrypted)
 318                 data_len -= CCMP_MIC_LEN;
 319
 320         /* First block, b_0 */
 321         b_0[0] = 0x59; /* flags: Adata: 1, M: 011, L: 001 */
 322         /* Nonce: Nonce Flags | A2 | PN
 323          * Nonce Flags: Priority (b0..b3) | Management (b4) | Reserved (b5..b7)
 324          */
 325         b_0[1] = qos_tid | (mgmt << 4);
 326         memcpy(&b_0[2], hdr->addr2, ETH_ALEN);
 327         memcpy(&b_0[8], pn, CCMP_PN_LEN);
 328         /* l(m) */
 329         put_unaligned_be16(data_len, &b_0[14]);
 330
 331         /* AAD (extra authenticate-only data) / masked 802.11 header
 332          * FC | A1 | A2 | A3 | SC | [A4] | [QC] */
 333         put_unaligned_be16(len_a, &aad[0]);
 334         put_unaligned(mask_fc, (__le16 *)&aad[2]);
 335         memcpy(&aad[4], &hdr->addr1, 3 * ETH_ALEN);
 336
 337         /* Mask Seq#, leave Frag# */
 338         aad[22] = *((u8 *) &hdr->seq_ctrl) & 0x0f;
 339         aad[23] = 0;
 340
 341         if (a4_included) {
 342                 memcpy(&aad[24], hdr->addr4, ETH_ALEN);
 343                 aad[30] = qos_tid;
 344                 aad[31] = 0;
 345         } else {
 346                 memset(&aad[24], 0, ETH_ALEN + IEEE80211_QOS_CTL_LEN);
 347                 aad[24] = qos_tid;
 348         }
 349 }
 350
 351
 352 static inline void ccmp_pn2hdr(u8 *hdr, u8 *pn, int key_id)
 353 {
 354         hdr[0] = pn[5];
 355         hdr[1] = pn[4];
 356         hdr[2] = 0;
 357         hdr[3] = 0x20 | (key_id << 6);
 358         hdr[4] = pn[3];
 359         hdr[5] = pn[2];
 360         hdr[6] = pn[1];
 361         hdr[7] = pn[0];
 362 }
 363
 364
 365 static inline void ccmp_hdr2pn(u8 *pn, u8 *hdr)
 366 {
 367         pn[0] = hdr[7];
 368         pn[1] = hdr[6];
 369         pn[2] = hdr[5];
 370         pn[3] = hdr[4];
 371         pn[4] = hdr[1];
 372         pn[5] = hdr[0];
 373 }
 374
 375
 376 static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 377 {
 378         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 379         struct ieee80211_key *key = tx->key;
 380         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 381         int hdrlen, len, tail;
 382         u8 *pos, *pn;
 383         int i;
 384
 385         if (info->control.hw_key &&
 386             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 387                 /*
 388                  * hwaccel has no need for preallocated room for CCMP
 389                  * header or MIC fields
 390                  */
 391                 return 0;
 392         }
 393
 394         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 395         len = skb->len - hdrlen;
 396
 397         if (info->control.hw_key)
 398                 tail = 0;
 399         else
 400                 tail = CCMP_MIC_LEN;
 401
 402         if (WARN_ON(skb_tailroom(skb) < tail ||
 403                     skb_headroom(skb) < CCMP_HDR_LEN))
 404                 return -1;
 405
 406         pos = skb_push(skb, CCMP_HDR_LEN);
 407         memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
 408         hdr = (struct ieee80211_hdr *) pos;
 409         pos += hdrlen;
 410
 411         /* PN = PN + 1 */
 412         pn = key->u.ccmp.tx_pn;
 413
 414         for (i = CCMP_PN_LEN - 1; i >= 0; i--) {
 415                 pn[i]++;
 416                 if (pn[i])
 417                         break;
 418         }
 419
 420         ccmp_pn2hdr(pos, pn, key->conf.keyidx);
 421
 422         /* hwaccel - with software CCMP header */
 423         if (info->control.hw_key)
 424                 return 0;
 425
 426         pos += CCMP_HDR_LEN;
 427         ccmp_special_blocks(skb, pn, key->u.ccmp.tx_crypto_buf, 0);
 428         ieee80211_aes_ccm_encrypt(key->u.ccmp.tfm, key->u.ccmp.tx_crypto_buf, pos, len,
 429                                   pos, skb_put(skb, CCMP_MIC_LEN));
 430
 431         return 0;
 432 }
 433
 434
 435 ieee80211_tx_result
 436 ieee80211_crypto_ccmp_encrypt(struct ieee80211_tx_data *tx)
 437 {
 438         struct sk_buff *skb = tx->skb;
 439
 440         ieee80211_tx_set_protected(tx);
 441
 442         do {
 443                 if (ccmp_encrypt_skb(tx, skb) < 0)
 444                         return TX_DROP;
 445         } while ((skb = skb->next));
 446
 447         return TX_CONTINUE;
 448 }
 449
 450
 451 ieee80211_rx_result
 452 ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
 453 {
 454         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 455         int hdrlen;
 456         struct ieee80211_key *key = rx->key;
 457         struct sk_buff *skb = rx->skb;
 458         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 459         u8 pn[CCMP_PN_LEN];
 460         int data_len;
 461         int queue;
 462
 463         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 464
 465         if (!ieee80211_is_data(hdr->frame_control) &&
 466             !ieee80211_is_robust_mgmt_frame(hdr))
 467                 return RX_CONTINUE;
 468
 469         data_len = skb->len - hdrlen - CCMP_HDR_LEN - CCMP_MIC_LEN;
 470         if (!rx->sta || data_len < 0)
 471                 return RX_DROP_UNUSABLE;
 472
 473         ccmp_hdr2pn(pn, skb->data + hdrlen);
 474
 475         queue = ieee80211_is_mgmt(hdr->frame_control) ?
 476                 NUM_RX_DATA_QUEUES : rx->queue;
 477
 478         if (memcmp(pn, key->u.ccmp.rx_pn[queue], CCMP_PN_LEN) <= 0) {
 479                 key->u.ccmp.replays++;
 480                 return RX_DROP_UNUSABLE;
 481         }
 482
 483         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 484                 /* hardware didn't decrypt/verify MIC */
 485                 ccmp_special_blocks(skb, pn, key->u.ccmp.rx_crypto_buf, 1);
 486
 487                 if (ieee80211_aes_ccm_decrypt(
 488                             key->u.ccmp.tfm, key->u.ccmp.rx_crypto_buf,
 489                             skb->data + hdrlen + CCMP_HDR_LEN, data_len,
 490                             skb->data + skb->len - CCMP_MIC_LEN,
 491                             skb->data + hdrlen + CCMP_HDR_LEN))
 492                         return RX_DROP_UNUSABLE;
 493         }
 494
 495         memcpy(key->u.ccmp.rx_pn[queue], pn, CCMP_PN_LEN);
 496
 497         /* Remove CCMP header and MIC */
 498         skb_trim(skb, skb->len - CCMP_MIC_LEN);
 499         memmove(skb->data + CCMP_HDR_LEN, skb->data, hdrlen);
 500         skb_pull(skb, CCMP_HDR_LEN);
 501
 502         return RX_CONTINUE;
 503 }
 504
 505
 506 static void bip_aad(struct sk_buff *skb, u8 *aad)
 507 {
 508         /* BIP AAD: FC(masked) || A1 || A2 || A3 */
 509
 510         /* FC type/subtype */
 511         aad[0] = skb->data[0];
 512         /* Mask FC Retry, PwrMgt, MoreData flags to zero */
 513         aad[1] = skb->data[1] & ~(BIT(4) | BIT(5) | BIT(6));
 514         /* A1 || A2 || A3 */
 515         memcpy(aad + 2, skb->data + 4, 3 * ETH_ALEN);
 516 }
 517
 518
 519 static inline void bip_ipn_swap(u8 *d, const u8 *s)
 520 {
 521         *d++ = s[5];
 522         *d++ = s[4];
 523         *d++ = s[3];
 524         *d++ = s[2];
 525         *d++ = s[1];
 526         *d = s[0];
 527 }
 528
 529
 530 ieee80211_tx_result
 531 ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
 532 {
 533         struct sk_buff *skb = tx->skb;
 534         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 535         struct ieee80211_key *key = tx->key;
 536         struct ieee80211_mmie *mmie;
 537         u8 *pn, aad[20];
 538         int i;
 539
 540         if (info->control.hw_key)
 541                 return 0;
 542
 543         if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
 544                 return TX_DROP;
 545
 546         mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
 547         mmie->element_id = WLAN_EID_MMIE;
 548         mmie->length = sizeof(*mmie) - 2;
 549         mmie->key_id = cpu_to_le16(key->conf.keyidx);
 550
 551         /* PN = PN + 1 */
 552         pn = key->u.aes_cmac.tx_pn;
 553
 554         for (i = sizeof(key->u.aes_cmac.tx_pn) - 1; i >= 0; i--) {
 555                 pn[i]++;
 556                 if (pn[i])
 557                         break;
 558         }
 559         bip_ipn_swap(mmie->sequence_number, pn);
 560
 561         bip_aad(skb, aad);
 562
 563         /*
 564          * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
 565          */
 566         ieee80211_aes_cmac(key->u.aes_cmac.tfm, key->u.aes_cmac.tx_crypto_buf,
 567                            aad, skb->data + 24, skb->len - 24, mmie->mic);
 568
 569         return TX_CONTINUE;
 570 }
 571
 572
 573 ieee80211_rx_result
 574 ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 575 {
 576         struct sk_buff *skb = rx->skb;
 577         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 578         struct ieee80211_key *key = rx->key;
 579         struct ieee80211_mmie *mmie;
 580         u8 aad[20], mic[8], ipn[6];
 581         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 582
 583         if (!ieee80211_is_mgmt(hdr->frame_control))
 584                 return RX_CONTINUE;
 585
 586         if (skb->len < 24 + sizeof(*mmie))
 587                 return RX_DROP_UNUSABLE;
 588
 589         mmie = (struct ieee80211_mmie *)
 590                 (skb->data + skb->len - sizeof(*mmie));
 591         if (mmie->element_id != WLAN_EID_MMIE ||
 592             mmie->length != sizeof(*mmie) - 2)
 593                 return RX_DROP_UNUSABLE; /* Invalid MMIE */
 594
 595         bip_ipn_swap(ipn, mmie->sequence_number);
 596
 597         if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 598                 key->u.aes_cmac.replays++;
 599                 return RX_DROP_UNUSABLE;
 600         }
 601
 602         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 603                 /* hardware didn't decrypt/verify MIC */
 604                 bip_aad(skb, aad);
 605                 ieee80211_aes_cmac(key->u.aes_cmac.tfm,
 606                                    key->u.aes_cmac.rx_crypto_buf, aad,
 607                                    skb->data + 24, skb->len - 24, mic);
 608                 if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
 609                         key->u.aes_cmac.icverrors++;
 610                         return RX_DROP_UNUSABLE;
 611                 }
 612         }
 613
 614         memcpy(key->u.aes_cmac.rx_pn, ipn, 6);
 615
 616         /* Remove MMIE */
 617         skb_trim(skb, skb->len - sizeof(*mmie));
 618
 619         return RX_CONTINUE;
 620 }