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, key_offset;
  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 authenticator;
  36         int tail;
  37
  38         hdr = (struct ieee80211_hdr *)skb->data;
  39         if (!tx->key || tx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
  40             skb->len < 24 || !ieee80211_is_data_present(hdr->frame_control))
  41                 return TX_CONTINUE;
  42
  43         hdrlen = ieee80211_hdrlen(hdr->frame_control);
  44         if (skb->len < hdrlen)
  45                 return TX_DROP;
  46
  47         data = skb->data + hdrlen;
  48         data_len = skb->len - hdrlen;
  49
  50         if (info->control.hw_key &&
  51             !(tx->flags & IEEE80211_TX_FRAGMENTED) &&
  52             !(tx->key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC)) {
  53                 /* hwaccel - with no need for SW-generated MMIC */
  54                 return TX_CONTINUE;
  55         }
  56
  57         tail = MICHAEL_MIC_LEN;
  58         if (!info->control.hw_key)
  59                 tail += TKIP_ICV_LEN;
  60
  61         if (WARN_ON(skb_tailroom(skb) < tail ||
  62                     skb_headroom(skb) < TKIP_IV_LEN))
  63                 return TX_DROP;
  64
  65 #if 0
  66         authenticator = fc & IEEE80211_FCTL_FROMDS; /* FIX */
  67 #else
  68         authenticator = 1;
  69 #endif
  70         key_offset = authenticator ?
  71                 NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY :
  72                 NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY;
  73         key = &tx->key->conf.key[key_offset];
  74         mic = skb_put(skb, MICHAEL_MIC_LEN);
  75         michael_mic(key, hdr, data, data_len, mic);
  76
  77         return TX_CONTINUE;
  78 }
  79
  80
  81 ieee80211_rx_result
  82 ieee80211_rx_h_michael_mic_verify(struct ieee80211_rx_data *rx)
  83 {
  84         u8 *data, *key = NULL, key_offset;
  85         size_t data_len;
  86         unsigned int hdrlen;
  87         u8 mic[MICHAEL_MIC_LEN];
  88         struct sk_buff *skb = rx->skb;
  89         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
  90         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
  91         int authenticator = 1, wpa_test = 0;
  92
  93         /* No way to verify the MIC if the hardware stripped it */
  94         if (status->flag & RX_FLAG_MMIC_STRIPPED)
  95                 return RX_CONTINUE;
  96
  97         if (!rx->key || rx->key->conf.cipher != WLAN_CIPHER_SUITE_TKIP ||
  98             !ieee80211_has_protected(hdr->frame_control) ||
  99             !ieee80211_is_data_present(hdr->frame_control))
 100                 return RX_CONTINUE;
 101
 102         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 103         if (skb->len < hdrlen + MICHAEL_MIC_LEN)
 104                 return RX_DROP_UNUSABLE;
 105
 106         data = skb->data + hdrlen;
 107         data_len = skb->len - hdrlen - MICHAEL_MIC_LEN;
 108
 109 #if 0
 110         authenticator = fc & IEEE80211_FCTL_TODS; /* FIX */
 111 #else
 112         authenticator = 1;
 113 #endif
 114         key_offset = authenticator ?
 115                 NL80211_TKIP_DATA_OFFSET_RX_MIC_KEY :
 116                 NL80211_TKIP_DATA_OFFSET_TX_MIC_KEY;
 117         key = &rx->key->conf.key[key_offset];
 118         michael_mic(key, hdr, data, data_len, mic);
 119         if (memcmp(mic, data + data_len, MICHAEL_MIC_LEN) != 0 || wpa_test) {
 120                 if (!(status->rx_flags & IEEE80211_RX_RA_MATCH))
 121                         return RX_DROP_UNUSABLE;
 122
 123                 mac80211_ev_michael_mic_failure(rx->sdata, rx->key->conf.keyidx,
 124                                                 (void *) skb->data, NULL,
 125                                                 GFP_ATOMIC);
 126                 return RX_DROP_UNUSABLE;
 127         }
 128
 129         /* remove Michael MIC from payload */
 130         skb_trim(skb, skb->len - MICHAEL_MIC_LEN);
 131
 132         /* update IV in key information to be able to detect replays */
 133         rx->key->u.tkip.rx[rx->queue].iv32 = rx->tkip_iv32;
 134         rx->key->u.tkip.rx[rx->queue].iv16 = rx->tkip_iv16;
 135
 136         return RX_CONTINUE;
 137 }
 138
 139
 140 static int tkip_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 141 {
 142         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 143         struct ieee80211_key *key = tx->key;
 144         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 145         unsigned int hdrlen;
 146         int len, tail;
 147         u8 *pos;
 148
 149         if (info->control.hw_key &&
 150             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 151                 /* hwaccel - with no need for software-generated IV */
 152                 return 0;
 153         }
 154
 155         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 156         len = skb->len - hdrlen;
 157
 158         if (info->control.hw_key)
 159                 tail = 0;
 160         else
 161                 tail = TKIP_ICV_LEN;
 162
 163         if (WARN_ON(skb_tailroom(skb) < tail ||
 164                     skb_headroom(skb) < TKIP_IV_LEN))
 165                 return -1;
 166
 167         pos = skb_push(skb, TKIP_IV_LEN);
 168         memmove(pos, pos + TKIP_IV_LEN, hdrlen);
 169         pos += hdrlen;
 170
 171         /* Increase IV for the frame */
 172         key->u.tkip.tx.iv16++;
 173         if (key->u.tkip.tx.iv16 == 0)
 174                 key->u.tkip.tx.iv32++;
 175
 176         pos = ieee80211_tkip_add_iv(pos, key, key->u.tkip.tx.iv16);
 177
 178         /* hwaccel - with software IV */
 179         if (info->control.hw_key)
 180                 return 0;
 181
 182         /* Add room for ICV */
 183         skb_put(skb, TKIP_ICV_LEN);
 184
 185         hdr = (struct ieee80211_hdr *) skb->data;
 186         return ieee80211_tkip_encrypt_data(tx->local->wep_tx_tfm,
 187                                            key, pos, len, hdr->addr2);
 188 }
 189
 190
 191 ieee80211_tx_result
 192 ieee80211_crypto_tkip_encrypt(struct ieee80211_tx_data *tx)
 193 {
 194         struct sk_buff *skb = tx->skb;
 195
 196         ieee80211_tx_set_protected(tx);
 197
 198         do {
 199                 if (tkip_encrypt_skb(tx, skb) < 0)
 200                         return TX_DROP;
 201         } while ((skb = skb->next));
 202
 203         return TX_CONTINUE;
 204 }
 205
 206
 207 ieee80211_rx_result
 208 ieee80211_crypto_tkip_decrypt(struct ieee80211_rx_data *rx)
 209 {
 210         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) rx->skb->data;
 211         int hdrlen, res, hwaccel = 0, wpa_test = 0;
 212         struct ieee80211_key *key = rx->key;
 213         struct sk_buff *skb = rx->skb;
 214         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 215
 216         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 217
 218         if (!ieee80211_is_data(hdr->frame_control))
 219                 return RX_CONTINUE;
 220
 221         if (!rx->sta || skb->len - hdrlen < 12)
 222                 return RX_DROP_UNUSABLE;
 223
 224         /*
 225          * Let TKIP code verify IV, but skip decryption.
 226          * In the case where hardware checks the IV as well,
 227          * we don't even get here, see ieee80211_rx_h_decrypt()
 228          */
 229         if (status->flag & RX_FLAG_DECRYPTED)
 230                 hwaccel = 1;
 231
 232         res = ieee80211_tkip_decrypt_data(rx->local->wep_rx_tfm,
 233                                           key, skb->data + hdrlen,
 234                                           skb->len - hdrlen, rx->sta->sta.addr,
 235                                           hdr->addr1, hwaccel, rx->queue,
 236                                           &rx->tkip_iv32,
 237                                           &rx->tkip_iv16);
 238         if (res != TKIP_DECRYPT_OK || wpa_test)
 239                 return RX_DROP_UNUSABLE;
 240
 241         /* Trim ICV */
 242         skb_trim(skb, skb->len - TKIP_ICV_LEN);
 243
 244         /* Remove IV */
 245         memmove(skb->data + TKIP_IV_LEN, skb->data, hdrlen);
 246         skb_pull(skb, TKIP_IV_LEN);
 247
 248         return RX_CONTINUE;
 249 }
 250
 251
 252 static void ccmp_special_blocks(struct sk_buff *skb, u8 *pn, u8 *scratch,
 253                                 int encrypted)
 254 {
 255         __le16 mask_fc;
 256         int a4_included, mgmt;
 257         u8 qos_tid;
 258         u8 *b_0, *aad;
 259         u16 data_len, len_a;
 260         unsigned int hdrlen;
 261         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 262
 263         b_0 = scratch + 3 * AES_BLOCK_LEN;
 264         aad = scratch + 4 * AES_BLOCK_LEN;
 265
 266         /*
 267          * Mask FC: zero subtype b4 b5 b6 (if not mgmt)
 268          * Retry, PwrMgt, MoreData; set Protected
 269          */
 270         mgmt = ieee80211_is_mgmt(hdr->frame_control);
 271         mask_fc = hdr->frame_control;
 272         mask_fc &= ~cpu_to_le16(IEEE80211_FCTL_RETRY |
 273                                 IEEE80211_FCTL_PM | IEEE80211_FCTL_MOREDATA);
 274         if (!mgmt)
 275                 mask_fc &= ~cpu_to_le16(0x0070);
 276         mask_fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
 277
 278         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 279         len_a = hdrlen - 2;
 280         a4_included = ieee80211_has_a4(hdr->frame_control);
 281
 282         if (ieee80211_is_data_qos(hdr->frame_control))
 283                 qos_tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;
 284         else
 285                 qos_tid = 0;
 286
 287         data_len = skb->len - hdrlen - CCMP_HDR_LEN;
 288         if (encrypted)
 289                 data_len -= CCMP_MIC_LEN;
 290
 291         /* First block, b_0 */
 292         b_0[0] = 0x59; /* flags: Adata: 1, M: 011, L: 001 */
 293         /* Nonce: Nonce Flags | A2 | PN
 294          * Nonce Flags: Priority (b0..b3) | Management (b4) | Reserved (b5..b7)
 295          */
 296         b_0[1] = qos_tid | (mgmt << 4);
 297         memcpy(&b_0[2], hdr->addr2, ETH_ALEN);
 298         memcpy(&b_0[8], pn, CCMP_PN_LEN);
 299         /* l(m) */
 300         put_unaligned_be16(data_len, &b_0[14]);
 301
 302         /* AAD (extra authenticate-only data) / masked 802.11 header
 303          * FC | A1 | A2 | A3 | SC | [A4] | [QC] */
 304         put_unaligned_be16(len_a, &aad[0]);
 305         put_unaligned(mask_fc, (__le16 *)&aad[2]);
 306         memcpy(&aad[4], &hdr->addr1, 3 * ETH_ALEN);
 307
 308         /* Mask Seq#, leave Frag# */
 309         aad[22] = *((u8 *) &hdr->seq_ctrl) & 0x0f;
 310         aad[23] = 0;
 311
 312         if (a4_included) {
 313                 memcpy(&aad[24], hdr->addr4, ETH_ALEN);
 314                 aad[30] = qos_tid;
 315                 aad[31] = 0;
 316         } else {
 317                 memset(&aad[24], 0, ETH_ALEN + IEEE80211_QOS_CTL_LEN);
 318                 aad[24] = qos_tid;
 319         }
 320 }
 321
 322
 323 static inline void ccmp_pn2hdr(u8 *hdr, u8 *pn, int key_id)
 324 {
 325         hdr[0] = pn[5];
 326         hdr[1] = pn[4];
 327         hdr[2] = 0;
 328         hdr[3] = 0x20 | (key_id << 6);
 329         hdr[4] = pn[3];
 330         hdr[5] = pn[2];
 331         hdr[6] = pn[1];
 332         hdr[7] = pn[0];
 333 }
 334
 335
 336 static inline void ccmp_hdr2pn(u8 *pn, u8 *hdr)
 337 {
 338         pn[0] = hdr[7];
 339         pn[1] = hdr[6];
 340         pn[2] = hdr[5];
 341         pn[3] = hdr[4];
 342         pn[4] = hdr[1];
 343         pn[5] = hdr[0];
 344 }
 345
 346
 347 static int ccmp_encrypt_skb(struct ieee80211_tx_data *tx, struct sk_buff *skb)
 348 {
 349         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 350         struct ieee80211_key *key = tx->key;
 351         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 352         int hdrlen, len, tail;
 353         u8 *pos, *pn;
 354         int i;
 355
 356         if (info->control.hw_key &&
 357             !(info->control.hw_key->flags & IEEE80211_KEY_FLAG_GENERATE_IV)) {
 358                 /*
 359                  * hwaccel has no need for preallocated room for CCMP
 360                  * header or MIC fields
 361                  */
 362                 return 0;
 363         }
 364
 365         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 366         len = skb->len - hdrlen;
 367
 368         if (info->control.hw_key)
 369                 tail = 0;
 370         else
 371                 tail = CCMP_MIC_LEN;
 372
 373         if (WARN_ON(skb_tailroom(skb) < tail ||
 374                     skb_headroom(skb) < CCMP_HDR_LEN))
 375                 return -1;
 376
 377         pos = skb_push(skb, CCMP_HDR_LEN);
 378         memmove(pos, pos + CCMP_HDR_LEN, hdrlen);
 379         hdr = (struct ieee80211_hdr *) pos;
 380         pos += hdrlen;
 381
 382         /* PN = PN + 1 */
 383         pn = key->u.ccmp.tx_pn;
 384
 385         for (i = CCMP_PN_LEN - 1; i >= 0; i--) {
 386                 pn[i]++;
 387                 if (pn[i])
 388                         break;
 389         }
 390
 391         ccmp_pn2hdr(pos, pn, key->conf.keyidx);
 392
 393         /* hwaccel - with software CCMP header */
 394         if (info->control.hw_key)
 395                 return 0;
 396
 397         pos += CCMP_HDR_LEN;
 398         ccmp_special_blocks(skb, pn, key->u.ccmp.tx_crypto_buf, 0);
 399         ieee80211_aes_ccm_encrypt(key->u.ccmp.tfm, key->u.ccmp.tx_crypto_buf, pos, len,
 400                                   pos, skb_put(skb, CCMP_MIC_LEN));
 401
 402         return 0;
 403 }
 404
 405
 406 ieee80211_tx_result
 407 ieee80211_crypto_ccmp_encrypt(struct ieee80211_tx_data *tx)
 408 {
 409         struct sk_buff *skb = tx->skb;
 410
 411         ieee80211_tx_set_protected(tx);
 412
 413         do {
 414                 if (ccmp_encrypt_skb(tx, skb) < 0)
 415                         return TX_DROP;
 416         } while ((skb = skb->next));
 417
 418         return TX_CONTINUE;
 419 }
 420
 421
 422 ieee80211_rx_result
 423 ieee80211_crypto_ccmp_decrypt(struct ieee80211_rx_data *rx)
 424 {
 425         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 426         int hdrlen;
 427         struct ieee80211_key *key = rx->key;
 428         struct sk_buff *skb = rx->skb;
 429         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 430         u8 pn[CCMP_PN_LEN];
 431         int data_len;
 432         int queue;
 433
 434         hdrlen = ieee80211_hdrlen(hdr->frame_control);
 435
 436         if (!ieee80211_is_data(hdr->frame_control) &&
 437             !ieee80211_is_robust_mgmt_frame(hdr))
 438                 return RX_CONTINUE;
 439
 440         data_len = skb->len - hdrlen - CCMP_HDR_LEN - CCMP_MIC_LEN;
 441         if (!rx->sta || data_len < 0)
 442                 return RX_DROP_UNUSABLE;
 443
 444         ccmp_hdr2pn(pn, skb->data + hdrlen);
 445
 446         queue = ieee80211_is_mgmt(hdr->frame_control) ?
 447                 NUM_RX_DATA_QUEUES : rx->queue;
 448
 449         if (memcmp(pn, key->u.ccmp.rx_pn[queue], CCMP_PN_LEN) <= 0) {
 450                 key->u.ccmp.replays++;
 451                 return RX_DROP_UNUSABLE;
 452         }
 453
 454         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 455                 /* hardware didn't decrypt/verify MIC */
 456                 ccmp_special_blocks(skb, pn, key->u.ccmp.rx_crypto_buf, 1);
 457
 458                 if (ieee80211_aes_ccm_decrypt(
 459                             key->u.ccmp.tfm, key->u.ccmp.rx_crypto_buf,
 460                             skb->data + hdrlen + CCMP_HDR_LEN, data_len,
 461                             skb->data + skb->len - CCMP_MIC_LEN,
 462                             skb->data + hdrlen + CCMP_HDR_LEN))
 463                         return RX_DROP_UNUSABLE;
 464         }
 465
 466         memcpy(key->u.ccmp.rx_pn[queue], pn, CCMP_PN_LEN);
 467
 468         /* Remove CCMP header and MIC */
 469         skb_trim(skb, skb->len - CCMP_MIC_LEN);
 470         memmove(skb->data + CCMP_HDR_LEN, skb->data, hdrlen);
 471         skb_pull(skb, CCMP_HDR_LEN);
 472
 473         return RX_CONTINUE;
 474 }
 475
 476
 477 static void bip_aad(struct sk_buff *skb, u8 *aad)
 478 {
 479         /* BIP AAD: FC(masked) || A1 || A2 || A3 */
 480
 481         /* FC type/subtype */
 482         aad[0] = skb->data[0];
 483         /* Mask FC Retry, PwrMgt, MoreData flags to zero */
 484         aad[1] = skb->data[1] & ~(BIT(4) | BIT(5) | BIT(6));
 485         /* A1 || A2 || A3 */
 486         memcpy(aad + 2, skb->data + 4, 3 * ETH_ALEN);
 487 }
 488
 489
 490 static inline void bip_ipn_swap(u8 *d, const u8 *s)
 491 {
 492         *d++ = s[5];
 493         *d++ = s[4];
 494         *d++ = s[3];
 495         *d++ = s[2];
 496         *d++ = s[1];
 497         *d = s[0];
 498 }
 499
 500
 501 ieee80211_tx_result
 502 ieee80211_crypto_aes_cmac_encrypt(struct ieee80211_tx_data *tx)
 503 {
 504         struct sk_buff *skb = tx->skb;
 505         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 506         struct ieee80211_key *key = tx->key;
 507         struct ieee80211_mmie *mmie;
 508         u8 *pn, aad[20];
 509         int i;
 510
 511         if (info->control.hw_key)
 512                 return 0;
 513
 514         if (WARN_ON(skb_tailroom(skb) < sizeof(*mmie)))
 515                 return TX_DROP;
 516
 517         mmie = (struct ieee80211_mmie *) skb_put(skb, sizeof(*mmie));
 518         mmie->element_id = WLAN_EID_MMIE;
 519         mmie->length = sizeof(*mmie) - 2;
 520         mmie->key_id = cpu_to_le16(key->conf.keyidx);
 521
 522         /* PN = PN + 1 */
 523         pn = key->u.aes_cmac.tx_pn;
 524
 525         for (i = sizeof(key->u.aes_cmac.tx_pn) - 1; i >= 0; i--) {
 526                 pn[i]++;
 527                 if (pn[i])
 528                         break;
 529         }
 530         bip_ipn_swap(mmie->sequence_number, pn);
 531
 532         bip_aad(skb, aad);
 533
 534         /*
 535          * MIC = AES-128-CMAC(IGTK, AAD || Management Frame Body || MMIE, 64)
 536          */
 537         ieee80211_aes_cmac(key->u.aes_cmac.tfm, key->u.aes_cmac.tx_crypto_buf,
 538                            aad, skb->data + 24, skb->len - 24, mmie->mic);
 539
 540         return TX_CONTINUE;
 541 }
 542
 543
 544 ieee80211_rx_result
 545 ieee80211_crypto_aes_cmac_decrypt(struct ieee80211_rx_data *rx)
 546 {
 547         struct sk_buff *skb = rx->skb;
 548         struct ieee80211_rx_status *status = IEEE80211_SKB_RXCB(skb);
 549         struct ieee80211_key *key = rx->key;
 550         struct ieee80211_mmie *mmie;
 551         u8 aad[20], mic[8], ipn[6];
 552         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 553
 554         if (!ieee80211_is_mgmt(hdr->frame_control))
 555                 return RX_CONTINUE;
 556
 557         if (skb->len < 24 + sizeof(*mmie))
 558                 return RX_DROP_UNUSABLE;
 559
 560         mmie = (struct ieee80211_mmie *)
 561                 (skb->data + skb->len - sizeof(*mmie));
 562         if (mmie->element_id != WLAN_EID_MMIE ||
 563             mmie->length != sizeof(*mmie) - 2)
 564                 return RX_DROP_UNUSABLE; /* Invalid MMIE */
 565
 566         bip_ipn_swap(ipn, mmie->sequence_number);
 567
 568         if (memcmp(ipn, key->u.aes_cmac.rx_pn, 6) <= 0) {
 569                 key->u.aes_cmac.replays++;
 570                 return RX_DROP_UNUSABLE;
 571         }
 572
 573         if (!(status->flag & RX_FLAG_DECRYPTED)) {
 574                 /* hardware didn't decrypt/verify MIC */
 575                 bip_aad(skb, aad);
 576                 ieee80211_aes_cmac(key->u.aes_cmac.tfm,
 577                                    key->u.aes_cmac.rx_crypto_buf, aad,
 578                                    skb->data + 24, skb->len - 24, mic);
 579                 if (memcmp(mic, mmie->mic, sizeof(mmie->mic)) != 0) {
 580                         key->u.aes_cmac.icverrors++;
 581                         return RX_DROP_UNUSABLE;
 582                 }
 583         }
 584
 585         memcpy(key->u.aes_cmac.rx_pn, ipn, 6);
 586
 587         /* Remove MMIE */
 588         skb_trim(skb, skb->len - sizeof(*mmie));
 589
 590         return RX_CONTINUE;
 591 }