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         int queue = rx->queue;
  90
  91         /* otherwise, TKIP is vulnerable to TID 0 vs. non-QoS replays */
  92         if (rx->queue == NUM_RX_DATA_QUEUES - 1)
  93                 queue = 0;
  94
  95         /*
  96          * it makes no sense to check for MIC errors on anything other
  97          * than data frames.
  98          */
  99         if (!ieee80211_is_data_present(hdr->frame_control))
 100                 return RX_CONTINUE;
 101
 102         /*
 103          * No way to verify the MIC if the hardware stripped it or
 104          * the IV with the key index. In this case we have solely rely
 105          * on the driver to set RX_FLAG_MMIC_ERROR in the event of a
 106          * MIC failure report.
 107          */
 108         if (status->flag & (RX_FLAG_MMIC_STRIPPED | RX_FLAG_IV_STRIPPED)) {
 109                 if (status->flag & RX_FLAG_MMIC_ERROR)
 110                         goto mic_fail;
 111
 112                 if (!(status->flag & RX_FLAG_IV_STRIPPED) && rx->key)
 113                         goto update_iv;
 114
 115                 return RX_CONTINUE;
 116         }
 117
 118         /*
 119          * Some hardware seems to generate Michael MIC failure reports; even
 120          * though, the frame was not encrypted with TKIP and therefore has no
 121          * MIC. Ignore the flag them to avoid triggering countermeasures.
 122          */
 123         if (!rx->key || rx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
 124             !(status->flag & RX_FLAG_DECRYPTED))
 125                 return RX_CONTINUE;
 126
 127         if (rx->sdata->vif.type == NL80211_IFTYPE_AP && rx->key->conf.keyidx) {
 128                 /*
 129                  * APs with pairwise keys should never receive Michael MIC
 130                  * errors for non-zero keyidx because these are reserved for
 131                  * group keys and only the AP is sending real multicast
 132                  * frames in the BSS. (
 133                  */
 134                 return RX_DROP_UNUSABLE;
 135         }
 136
 137         if (status->flag & RX_FLAG_MMIC_ERROR)
 138                 goto mic_fail;
 139
 140         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 141         if (skb->len < hdrlen + MICHAEL_MIC_LEN)
 142                 return RX_DROP_UNUSABLE;
 143
 144         data = skb->data + hdrlen;
 145         data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
 146         key = &rx->key->conf.key[NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY];
 147         michael_mic(key, hdr, data, data_len, mic);
 148         if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0)
 149                 goto mic_fail;
 150
 151         /* remove Michael MIC from payload */
 152         skb_trim(skb, skb->len - MICHAEL_MIC_LEN);
 153
 154 update_iv:
 155         /* update IV in key information to be able to detect replays */
 156         rx->key->u.tkip.rx[queue].iv32 = rx->tkip_iv32;
 157         rx->key->u.tkip.rx[queue].iv16 = rx->tkip_iv16;
 158
 159         return RX_CONTINUE;
 160
 161 mic_fail:
 162         /*
 163          * In some cases the key can be unset - e.g. a multicast packet, in
 164          * a driver that supports HW encryption. Send up the key idx only if
 165          * the key is set.
 166          */
 167         mac80211_ev_michael_mic_failure(rx->sdata,
 168                                         rx->key ? rx->key->conf.keyidx : -1,
 169                                         (void *) skb->data, NULL, GFP_ATOMIC);
 170         return RX_DROP_UNUSABLE;
 171 }
 172
 173
 174 static int tkip_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 175 {
 176         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 177         struct ieee80211_key *key = tx->key;
 178         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 179         unsigned int hdrlen;
 180         int len, tail;
 181         u8 *pos;
 182
 183         if (info->control.hw_key &&
 184             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 185                 /* hwaccel - with no need for software-generated IV */
 186                 return 0;
 187         }
 188
 189         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 190         len = skb->len - hdrlen;
 191
 192         if (info->control.hw_key)
 193                 tail = 0;
 194         else
 195                 tail = TKIP_ICV_LEN;
 196
 197         if (WARN_ON(skb_tailroom(skb) < tail ||
 198                     skb_headroom(skb) < TKIP_IV_LEN))
 199                 return -1;
 200
 201         pos = skb_push(skb, TKIP_IV_LEN);
 202         memmove(pos, pos + TKIP_IV_LEN, hdrlen);
 203         pos += hdrlen;
 204
 205         /* Increase IV for the frame */
 206         key->u.tkip.tx.iv16++;
 207         if (key->u.tkip.tx.iv16 == 0)
 208                 key->u.tkip.tx.iv32++;
 209
 210         pos = ieee80211_tkip_add_iv(pos, key, key->u.tkip.tx.iv16);
 211
 212         /* hwaccel - with software IV */
 213         if (info->control.hw_key)
 214                 return 0;
 215
 216         /* Add room for ICV */
 217         skb_put(skb, TKIP_ICV_LEN);
 218
 219         hdr = (struct ieee80211_hdr *) skb->data;
 220         return ieee80211_tkip_encrypt_data(tx->local->wep_tx_tfm,
 221                                            key, pos, len, hdr->addr2);
 222 }
 223
 224
 225 ieee80211_tx_result
 226 ieee80211_crypto_tkip_encrypt(struct ieee80211_tx_data *tx)
 227 {
 228         struct sk_buff *skb = tx->skb;
 229
 230         ieee80211_tx_set_protected(tx);
 231
 232         do {
 233                 if (tkip_encrypt_skb(tx, skb) < 0)
 234                         return TX_DROP;
 235         } while ((skb = skb->next));
 236
 237         return TX_CONTINUE;
 238 }
 239
 240
 241 ieee80211_rx_result
 242 ieee80211_crypto_tkip_decrypt(struct ieee80211_rx_data *rx)
 243 {
 244         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
 245         int hdrlen, res, hwaccel = 0;
 246         struct ieee80211_key *key = rx->key;
 247         struct sk_buff *skb = rx->skb;
 248         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 249         int queue = rx->queue;
 250
 251         /* otherwise, TKIP is vulnerable to TID 0 vs. non-QoS replays */
 252         if (rx->queue == NUM_RX_DATA_QUEUES - 1)
 253                 queue = 0;
 254
 255         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 256
 257         if (!ieee80211_is_data(hdr->frame_control))
 258                 return RX_CONTINUE;
 259
 260         if (!rx->sta || skb->len - hdrlen < 12)
 261                 return RX_DROP_UNUSABLE;
 262
 263         /*
 264          * Let TKIP code verify IV, but skip decryption.
 265          * In the case where hardware checks the IV as well,
 266          * we don't even get here, see ieee80211_rx_h_decrypt()
 267          */
 268         if (status->flag & RX_FLAG_DECRYPTED)
 269                 hwaccel = 1;
 270
 271         res = ieee80211_tkip_decrypt_data(rx->local->wep_rx_tfm,
 272                                           key, skb->data + hdrlen,
 273                                           skb->len - hdrlen, rx->sta->sta.addr,
 274                                           hdr->addr1, hwaccel, queue,
 275                                           &rx->tkip_iv32,
 276                                           &rx->tkip_iv16);
 277         if (res != TKIP_DECRYPT_OK)
 278                 return RX_DROP_UNUSABLE;
 279
 280         /* Trim ICV */
 281         skb_trim(skb, skb->len - TKIP_ICV_LEN);
 282
 283         /* Remove IV */
 284         memmove(skb->data + TKIP_IV_LEN, skb->data, hdrlen);
 285         skb_pull(skb, TKIP_IV_LEN);
 286
 287         return RX_CONTINUE;
 288 }
 289
 290
 291 static void ccmp_special_blocks(struct sk_buff *skb, u8 *pn, u8 *scratch,
 292                                 int encrypted)
 293 {
 294         __le16 mask_fc;
 295         int a4_included, mgmt;
 296         u8 qos_tid;
 297         u8 *b_0, *aad;
 298         u16 data_len, len_a;
 299         unsigned int hdrlen;
 300         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 301
 302         b_0 = scratch + 3 * AES_BLOCK_LEN;
 303         aad = scratch + 4 * AES_BLOCK_LEN;
 304
 305         /*
 306          * Mask FC: zero subtype b4 b5 b6 (if not mgmt)
 307          * Retry, PwrMgt, MoreData; set Protected
 308          */
 309         mgmt = ieee80211_is_mgmt(hdr->frame_control);
 310         mask_fc = hdr->frame_control;
 311         mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY |
 312                                 IEEE80211_FCTL_PM | IEEE80211_FCTL_MOREDATA);
 313         if (!mgmt)
 314                 mask_fc &= ~cpu_to_le16(0x0070);
 315         mask_fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 316
 317         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 318         len_a = hdrlen - 2;
 319         a4_included = ieee80211_has_a4(hdr->frame_control);
 320
 321         if (ieee80211_is_data_qos(hdr->frame_control))
 322                 qos_tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
 323         else
 324                 qos_tid = 0;
 325
 326         data_len = skb->len - hdrlen - CCMP_HDR_LEN;
 327         if (encrypted)
 328                 data_len -= CCMP_MIC_LEN;
 329
 330         /* First block, b_0 */
 331         b_0[0] = 0x59; /* flags: Adata: 1, M: 011, L: 001 */
 332         /* Nonce: Nonce Flags | A2 | PN
 333          * Nonce Flags: Priority (b0..b3) | Management (b4) | Reserved (b5..b7)
 334          */
 335         b_0[1] = qos_tid | (mgmt << 4);
 336         memcpy(&b_0[2], hdr->addr2, ETH_ALEN);
 337         memcpy(&b_0[8], pn, CCMP_PN_LEN);
 338         /* l(m) */
 339         put_unaligned_be16(data_len, &b_0[14]);
 340
 341         /* AAD (extra authenticate-only data) / masked 802.11 header
 342          * FC | A1 | A2 | A3 | SC | [A4] | [QC] */
 343         put_unaligned_be16(len_a, &aad[0]);
 344         put_unaligned(mask_fc, (__le16 *)&aad[2]);
 345         memcpy(&aad[4], &hdr->addr1, 3 * ETH_ALEN);
 346
 347         /* Mask Seq#, leave Frag# */
 348         aad[22] = *((u8 *) &hdr->seq_ctrl) & 0x0f;
 349         aad[23] = 0;
 350
 351         if (a4_included) {
 352                 memcpy(&aad[24], hdr->addr4, ETH_ALEN);
 353                 aad[30] = qos_tid;
 354                 aad[31] = 0;
 355         } else {
 356                 memset(&aad[24], 0, ETH_ALEN + IEEE80211_QOS_CTL_LEN);
 357                 aad[24] = qos_tid;
 358         }
 359 }
 360
 361
 362 static inline void ccmp_pn2hdr(u8 *hdr, u8 *pn, int key_id)
 363 {
 364         hdr[0] = pn[5];
 365         hdr[1] = pn[4];
 366         hdr[2] = 0;
 367         hdr[3] = 0x20 | (key_id << 6);
 368         hdr[4] = pn[3];
 369         hdr[5] = pn[2];
 370         hdr[6] = pn[1];
 371         hdr[7] = pn[0];
 372 }
 373
 374
 375 static inline void ccmp_hdr2pn(u8 *pn, u8 *hdr)
 376 {
 377         pn[0] = hdr[7];
 378         pn[1] = hdr[6];
 379         pn[2] = hdr[5];
 380         pn[3] = hdr[4];
 381         pn[4] = hdr[1];
 382         pn[5] = hdr[0];
 383 }
 384
 385
 386 static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 387 {
 388         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 389         struct ieee80211_key *key = tx->key;
 390         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 391         int hdrlen, len, tail;
 392         u8 *pos, *pn;
 393         int i;
 394
 395         if (info->control.hw_key &&
 396             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 397                 /*
 398                  * hwaccel has no need for preallocated room for CCMP
 399                  * header or MIC fields
 400                  */
 401                 return 0;
 402         }
 403
 404         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 405         len = skb->len - hdrlen;
 406
 407         if (info->control.hw_key)
 408                 tail = 0;
 409         else
 410                 tail = CCMP_MIC_LEN;
 411
 412         if (WARN_ON(skb_tailroom(skb) < tail ||
 413                     skb_headroom(skb) < CCMP_HDR_LEN))
 414                 return -1;
 415
 416         pos = skb_push(skb, CCMP_HDR_LEN);
 417         memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
 418         hdr = (struct ieee80211_hdr *) pos;
 419         pos += hdrlen;
 420
 421         /* PN = PN + 1 */
 422         pn = key->u.ccmp.tx_pn;
 423
 424         for (i = CCMP_PN_LEN - 1; i >= 0; i--) {
 425                 pn[i]++;
 426                 if (pn[i])
 427                         break;
 428         }
 429
 430         ccmp_pn2hdr(pos, pn, key->conf.keyidx);
 431
 432         /* hwaccel - with software CCMP header */
 433         if (info->control.hw_key)
 434                 return 0;
 435
 436         pos += CCMP_HDR_LEN;
 437         ccmp_special_blocks(skb, pn, key->u.ccmp.tx_crypto_buf, 0);
 438         ieee80211_aes_ccm_encrypt(key->u.ccmp.tfm, key->u.ccmp.tx_crypto_buf, pos, len,
 439                                   pos, skb_put(skb, CCMP_MIC_LEN));
 440
 441         return 0;
 442 }
 443
 444
 445 ieee80211_tx_result
 446 ieee80211_crypto_ccmp_encrypt(struct ieee80211_tx_data *tx)
 447 {
 448         struct sk_buff *skb = tx->skb;
 449
 450         ieee80211_tx_set_protected(tx);
 451
 452         do {
 453                 if (ccmp_encrypt_skb(tx, skb) < 0)
 454                         return TX_DROP;
 455         } while ((skb = skb->next));
 456
 457         return TX_CONTINUE;
 458 }
 459
 460
 461 ieee80211_rx_result
 462 ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
 463 {
 464         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 465         int hdrlen;
 466         struct ieee80211_key *key = rx->key;
 467         struct sk_buff *skb = rx->skb;
 468         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 469         u8 pn[CCMP_PN_LEN];
 470         int data_len;
 471         int queue;
 472
 473         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 474
 475         if (!ieee80211_is_data(hdr->frame_control) &&
 476             !ieee80211_is_robust_mgmt_frame(hdr))
 477                 return RX_CONTINUE;
 478
 479         data_len = skb->len - hdrlen - CCMP_HDR_LEN - CCMP_MIC_LEN;
 480         if (!rx->sta || data_len < 0)
 481                 return RX_DROP_UNUSABLE;
 482
 483         ccmp_hdr2pn(pn, skb->data + hdrlen);
 484
 485         queue = ieee80211_is_mgmt(hdr->frame_control) ?
 486                 NUM_RX_DATA_QUEUES : rx->queue;
 487
 488         if (memcmp(pn, key->u.ccmp.rx_pn[queue], CCMP_PN_LEN) <= 0) {
 489                 key->u.ccmp.replays++;
 490                 return RX_DROP_UNUSABLE;
 491         }
 492
 493         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 494                 /* hardware didn't decrypt/verify MIC */
 495                 ccmp_special_blocks(skb, pn, key->u.ccmp.rx_crypto_buf, 1);
 496
 497                 if (ieee80211_aes_ccm_decrypt(
 498                             key->u.ccmp.tfm, key->u.ccmp.rx_crypto_buf,
 499                             skb->data + hdrlen + CCMP_HDR_LEN, data_len,
 500                             skb->data + skb->len - CCMP_MIC_LEN,
 501                             skb->data + hdrlen + CCMP_HDR_LEN))
 502                         return RX_DROP_UNUSABLE;
 503         }
 504
 505         memcpy(key->u.ccmp.rx_pn[queue], pn, CCMP_PN_LEN);
 506
 507         /* Remove CCMP header and MIC */
 508         skb_trim(skb, skb->len - CCMP_MIC_LEN);
 509         memmove(skb->data + CCMP_HDR_LEN, skb->data, hdrlen);
 510         skb_pull(skb, CCMP_HDR_LEN);
 511
 512         return RX_CONTINUE;
 513 }
 514
 515
 516 static void bip_aad(struct sk_buff *skb, u8 *aad)
 517 {
 518         /* BIP AAD: FC(masked) || A1 || A2 || A3 */
 519
 520         /* FC type/subtype */
 521         aad[0] = skb->data[0];
 522         /* Mask FC Retry, PwrMgt, MoreData flags to zero */
 523         aad[1] = skb->data[1] & ~(BIT(4) | BIT(5) | BIT(6));
 524         /* A1 || A2 || A3 */
 525         memcpy(aad + 2, skb->data + 4, 3 * ETH_ALEN);
 526 }
 527
 528
 529 static inline void bip_ipn_swap(u8 *d, const u8 *s)
 530 {
 531         *d++ = s[5];
 532         *d++ = s[4];
 533         *d++ = s[3];
 534         *d++ = s[2];
 535         *d++ = s[1];
 536         *d = s[0];
 537 }
 538
 539
 540 ieee80211_tx_result
 541 ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
 542 {
 543         struct sk_buff *skb = tx->skb;
 544         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 545         struct ieee80211_key *key = tx->key;
 546         struct ieee80211_mmie *mmie;
 547         u8 *pn, aad[20];
 548         int i;
 549
 550         if (info->control.hw_key)
 551                 return 0;
 552
 553         if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
 554                 return TX_DROP;
 555
 556         mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
 557         mmie->element_id = WLAN_EID_MMIE;
 558         mmie->length = sizeof(*mmie) - 2;
 559         mmie->key_id = cpu_to_le16(key->conf.keyidx);
 560
 561         /* PN = PN + 1 */
 562         pn = key->u.aes_cmac.tx_pn;
 563
 564         for (i = sizeof(key->u.aes_cmac.tx_pn) - 1; i >= 0; i--) {
 565                 pn[i]++;
 566                 if (pn[i])
 567                         break;
 568         }
 569         bip_ipn_swap(mmie->sequence_number, pn);
 570
 571         bip_aad(skb, aad);
 572
 573         /*
 574          * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
 575          */
 576         ieee80211_aes_cmac(key->u.aes_cmac.tfm, key->u.aes_cmac.tx_crypto_buf,
 577                            aad, skb->data + 24, skb->len - 24, mmie->mic);
 578
 579         return TX_CONTINUE;
 580 }
 581
 582
 583 ieee80211_rx_result
 584 ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 585 {
 586         struct sk_buff *skb = rx->skb;
 587         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 588         struct ieee80211_key *key = rx->key;
 589         struct ieee80211_mmie *mmie;
 590         u8 aad[20], mic[8], ipn[6];
 591         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 592
 593         if (!ieee80211_is_mgmt(hdr->frame_control))
 594                 return RX_CONTINUE;
 595
 596         if (skb->len < 24 + sizeof(*mmie))
 597                 return RX_DROP_UNUSABLE;
 598
 599         mmie = (struct ieee80211_mmie *)
 600                 (skb->data + skb->len - sizeof(*mmie));
 601         if (mmie->element_id != WLAN_EID_MMIE ||
 602             mmie->length != sizeof(*mmie) - 2)
 603                 return RX_DROP_UNUSABLE; /* Invalid MMIE */
 604
 605         bip_ipn_swap(ipn, mmie->sequence_number);
 606
 607         if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 608                 key->u.aes_cmac.replays++;
 609                 return RX_DROP_UNUSABLE;
 610         }
 611
 612         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 613                 /* hardware didn't decrypt/verify MIC */
 614                 bip_aad(skb, aad);
 615                 ieee80211_aes_cmac(key->u.aes_cmac.tfm,
 616                                    key->u.aes_cmac.rx_crypto_buf, aad,
 617                                    skb->data + 24, skb->len - 24, mic);
 618                 if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
 619                         key->u.aes_cmac.icverrors++;
 620                         return RX_DROP_UNUSABLE;
 621                 }
 622         }
 623
 624         memcpy(key->u.aes_cmac.rx_pn, ipn, 6);
 625
 626         /* Remove MMIE */
 627         skb_trim(skb, skb->len - sizeof(*mmie));
 628
 629         return RX_CONTINUE;
 630 }