net/mac80211/fils_aead.c

   1 /*
   2  * FILS AEAD for (Re)Association Request/Response frames
   3  * Copyright 2016, Qualcomm Atheros, Inc.
   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 <crypto/aes.h>
  11 #include <crypto/algapi.h>
  12 #include <crypto/skcipher.h>
  13
  14 #include "ieee80211_i.h"
  15 #include "aes_cmac.h"
  16 #include "fils_aead.h"
  17
  18 static int aes_s2v(struct crypto_cipher *tfm,
  19                    size_t num_elem, const u8 *addr[], size_t len[], u8 *v)
  20 {
  21         u8 d[AES_BLOCK_SIZE], tmp[AES_BLOCK_SIZE];
  22         size_t i;
  23         const u8 *data[2];
  24         size_t data_len[2], data_elems;
  25
  26         /* D = AES-CMAC(K, <zero>) */
  27         memset(tmp, 0, AES_BLOCK_SIZE);
  28         data[0] = tmp;
  29         data_len[0] = AES_BLOCK_SIZE;
  30         aes_cmac_vector(tfm, 1, data, data_len, d, AES_BLOCK_SIZE);
  31
  32         for (i = 0; i < num_elem - 1; i++) {
  33                 /* D = dbl(D) xor AES_CMAC(K, Si) */
  34                 gf_mulx(d); /* dbl */
  35                 aes_cmac_vector(tfm, 1, &addr[i], &len[i], tmp,
  36                                 AES_BLOCK_SIZE);
  37                 crypto_xor(d, tmp, AES_BLOCK_SIZE);
  38         }
  39
  40         if (len[i] >= AES_BLOCK_SIZE) {
  41                 /* len(Sn) >= 128 */
  42                 size_t j;
  43                 const u8 *pos;
  44
  45                 /* T = Sn xorend D */
  46
  47                 /* Use a temporary buffer to perform xorend on Sn (addr[i]) to
  48                  * avoid modifying the const input argument.
  49                  */
  50                 data[0] = addr[i];
  51                 data_len[0] = len[i] - AES_BLOCK_SIZE;
  52                 pos = addr[i] + data_len[0];
  53                 for (j = 0; j < AES_BLOCK_SIZE; j++)
  54                         tmp[j] = pos[j] ^ d[j];
  55                 data[1] = tmp;
  56                 data_len[1] = AES_BLOCK_SIZE;
  57                 data_elems = 2;
  58         } else {
  59                 /* len(Sn) < 128 */
  60                 /* T = dbl(D) xor pad(Sn) */
  61                 gf_mulx(d); /* dbl */
  62                 memset(tmp, 0, AES_BLOCK_SIZE);
  63                 memcpy(tmp, addr[i], len[i]);
  64                 tmp[len[i]] = 0x80;
  65                 crypto_xor(d, tmp, AES_BLOCK_SIZE);
  66                 data[0] = d;
  67                 data_len[0] = sizeof(d);
  68                 data_elems = 1;
  69         }
  70         /* V = AES-CMAC(K, T) */
  71         aes_cmac_vector(tfm, data_elems, data, data_len, v, AES_BLOCK_SIZE);
  72
  73         return 0;
  74 }
  75
  76 /* Note: addr[] and len[] needs to have one extra slot at the end. */
  77 static int aes_siv_encrypt(const u8 *key, size_t key_len,
  78                            const u8 *plain, size_t plain_len,
  79                            size_t num_elem, const u8 *addr[],
  80                            size_t len[], u8 *out)
  81 {
  82         u8 v[AES_BLOCK_SIZE];
  83         struct crypto_cipher *tfm;
  84         struct crypto_skcipher *tfm2;
  85         struct skcipher_request *req;
  86         int res;
  87         struct scatterlist src[1], dst[1];
  88         u8 *tmp;
  89
  90         key_len /= 2; /* S2V key || CTR key */
  91
  92         addr[num_elem] = plain;
  93         len[num_elem] = plain_len;
  94         num_elem++;
  95
  96         /* S2V */
  97
  98         tfm = crypto_alloc_cipher("aes", 0, 0);
  99         if (IS_ERR(tfm))
 100                 return PTR_ERR(tfm);
 101         /* K1 for S2V */
 102         res = crypto_cipher_setkey(tfm, key, key_len);
 103         if (!res)
 104                 res = aes_s2v(tfm, num_elem, addr, len, v);
 105         crypto_free_cipher(tfm);
 106         if (res)
 107                 return res;
 108
 109         /* Use a temporary buffer of the plaintext to handle need for
 110          * overwriting this during AES-CTR.
 111          */
 112         tmp = kmemdup(plain, plain_len, GFP_KERNEL);
 113         if (!tmp)
 114                 return -ENOMEM;
 115
 116         /* IV for CTR before encrypted data */
 117         memcpy(out, v, AES_BLOCK_SIZE);
 118
 119         /* Synthetic IV to be used as the initial counter in CTR:
 120          * Q = V bitand (1^64 || 0^1 || 1^31 || 0^1 || 1^31)
 121          */
 122         v[8] &= 0x7f;
 123         v[12] &= 0x7f;
 124
 125         /* CTR */
 126
 127         tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, 0);
 128         if (IS_ERR(tfm2)) {
 129                 kfree(tmp);
 130                 return PTR_ERR(tfm2);
 131         }
 132         /* K2 for CTR */
 133         res = crypto_skcipher_setkey(tfm2, key + key_len, key_len);
 134         if (res)
 135                 goto fail;
 136
 137         req = skcipher_request_alloc(tfm2, GFP_KERNEL);
 138         if (!req) {
 139                 res = -ENOMEM;
 140                 goto fail;
 141         }
 142
 143         sg_init_one(src, tmp, plain_len);
 144         sg_init_one(dst, out + AES_BLOCK_SIZE, plain_len);
 145         skcipher_request_set_crypt(req, src, dst, plain_len, v);
 146         res = crypto_skcipher_encrypt(req);
 147         skcipher_request_free(req);
 148 fail:
 149         kfree(tmp);
 150         crypto_free_skcipher(tfm2);
 151         return res;
 152 }
 153
 154 /* Note: addr[] and len[] needs to have one extra slot at the end. */
 155 static int aes_siv_decrypt(const u8 *key, size_t key_len,
 156                            const u8 *iv_crypt, size_t iv_c_len,
 157                            size_t num_elem, const u8 *addr[], size_t len[],
 158                            u8 *out)
 159 {
 160         struct crypto_cipher *tfm;
 161         struct crypto_skcipher *tfm2;
 162         struct skcipher_request *req;
 163         struct scatterlist src[1], dst[1];
 164         size_t crypt_len;
 165         int res;
 166         u8 frame_iv[AES_BLOCK_SIZE], iv[AES_BLOCK_SIZE];
 167         u8 check[AES_BLOCK_SIZE];
 168
 169         crypt_len = iv_c_len - AES_BLOCK_SIZE;
 170         key_len /= 2; /* S2V key || CTR key */
 171         addr[num_elem] = out;
 172         len[num_elem] = crypt_len;
 173         num_elem++;
 174
 175         memcpy(iv, iv_crypt, AES_BLOCK_SIZE);
 176         memcpy(frame_iv, iv_crypt, AES_BLOCK_SIZE);
 177
 178         /* Synthetic IV to be used as the initial counter in CTR:
 179          * Q = V bitand (1^64 || 0^1 || 1^31 || 0^1 || 1^31)
 180          */
 181         iv[8] &= 0x7f;
 182         iv[12] &= 0x7f;
 183
 184         /* CTR */
 185
 186         tfm2 = crypto_alloc_skcipher("ctr(aes)", 0, 0);
 187         if (IS_ERR(tfm2))
 188                 return PTR_ERR(tfm2);
 189         /* K2 for CTR */
 190         res = crypto_skcipher_setkey(tfm2, key + key_len, key_len);
 191         if (res) {
 192                 crypto_free_skcipher(tfm2);
 193                 return res;
 194         }
 195
 196         req = skcipher_request_alloc(tfm2, GFP_KERNEL);
 197         if (!req) {
 198                 crypto_free_skcipher(tfm2);
 199                 return -ENOMEM;
 200         }
 201
 202         sg_init_one(src, iv_crypt + AES_BLOCK_SIZE, crypt_len);
 203         sg_init_one(dst, out, crypt_len);
 204         skcipher_request_set_crypt(req, src, dst, crypt_len, iv);
 205         res = crypto_skcipher_decrypt(req);
 206         skcipher_request_free(req);
 207         crypto_free_skcipher(tfm2);
 208         if (res)
 209                 return res;
 210
 211         /* S2V */
 212
 213         tfm = crypto_alloc_cipher("aes", 0, 0);
 214         if (IS_ERR(tfm))
 215                 return PTR_ERR(tfm);
 216         /* K1 for S2V */
 217         res = crypto_cipher_setkey(tfm, key, key_len);
 218         if (!res)
 219                 res = aes_s2v(tfm, num_elem, addr, len, check);
 220         crypto_free_cipher(tfm);
 221         if (res)
 222                 return res;
 223         if (memcmp(check, frame_iv, AES_BLOCK_SIZE) != 0)
 224                 return -EINVAL;
 225         return 0;
 226 }
 227
 228 int fils_encrypt_assoc_req(struct sk_buff *skb,
 229                            struct ieee80211_mgd_assoc_data *assoc_data)
 230 {
 231         struct ieee80211_mgmt *mgmt = (void *)skb->data;
 232         u8 *capab, *ies, *encr;
 233         const u8 *addr[5 + 1], *session;
 234         size_t len[5 + 1];
 235         size_t crypt_len;
 236
 237         if (ieee80211_is_reassoc_req(mgmt->frame_control)) {
 238                 capab = (u8 *)&mgmt->u.reassoc_req.capab_info;
 239                 ies = mgmt->u.reassoc_req.variable;
 240         } else {
 241                 capab = (u8 *)&mgmt->u.assoc_req.capab_info;
 242                 ies = mgmt->u.assoc_req.variable;
 243         }
 244
 245         session = cfg80211_find_ext_ie(WLAN_EID_EXT_FILS_SESSION,
 246                                        ies, skb->data + skb->len - ies);
 247         if (!session || session[1] != 1 + 8)
 248                 return -EINVAL;
 249         /* encrypt after FILS Session element */
 250         encr = (u8 *)session + 2 + 1 + 8;
 251
 252         /* AES-SIV AAD vectors */
 253
 254         /* The STA's MAC address */
 255         addr[0] = mgmt->sa;
 256         len[0] = ETH_ALEN;
 257         /* The AP's BSSID */
 258         addr[1] = mgmt->da;
 259         len[1] = ETH_ALEN;
 260         /* The STA's nonce */
 261         addr[2] = assoc_data->fils_nonces;
 262         len[2] = FILS_NONCE_LEN;
 263         /* The AP's nonce */
 264         addr[3] = &assoc_data->fils_nonces[FILS_NONCE_LEN];
 265         len[3] = FILS_NONCE_LEN;
 266         /* The (Re)Association Request frame from the Capability Information
 267          * field to the FILS Session element (both inclusive).
 268          */
 269         addr[4] = capab;
 270         len[4] = encr - capab;
 271
 272         crypt_len = skb->data + skb->len - encr;
 273         skb_put(skb, AES_BLOCK_SIZE);
 274         return aes_siv_encrypt(assoc_data->fils_kek, assoc_data->fils_kek_len,
 275                                encr, crypt_len, 5, addr, len, encr);
 276 }
 277
 278 int fils_decrypt_assoc_resp(struct ieee80211_sub_if_data *sdata,
 279                             u8 *frame, size_t *frame_len,
 280                             struct ieee80211_mgd_assoc_data *assoc_data)
 281 {
 282         struct ieee80211_mgmt *mgmt = (void *)frame;
 283         u8 *capab, *ies, *encr;
 284         const u8 *addr[5 + 1], *session;
 285         size_t len[5 + 1];
 286         int res;
 287         size_t crypt_len;
 288
 289         if (*frame_len < 24 + 6)
 290                 return -EINVAL;
 291
 292         capab = (u8 *)&mgmt->u.assoc_resp.capab_info;
 293         ies = mgmt->u.assoc_resp.variable;
 294         session = cfg80211_find_ext_ie(WLAN_EID_EXT_FILS_SESSION,
 295                                        ies, frame + *frame_len - ies);
 296         if (!session || session[1] != 1 + 8) {
 297                 mlme_dbg(sdata,
 298                          "No (valid) FILS Session element in (Re)Association Response frame from %pM",
 299                          mgmt->sa);
 300                 return -EINVAL;
 301         }
 302         /* decrypt after FILS Session element */
 303         encr = (u8 *)session + 2 + 1 + 8;
 304
 305         /* AES-SIV AAD vectors */
 306
 307         /* The AP's BSSID */
 308         addr[0] = mgmt->sa;
 309         len[0] = ETH_ALEN;
 310         /* The STA's MAC address */
 311         addr[1] = mgmt->da;
 312         len[1] = ETH_ALEN;
 313         /* The AP's nonce */
 314         addr[2] = &assoc_data->fils_nonces[FILS_NONCE_LEN];
 315         len[2] = FILS_NONCE_LEN;
 316         /* The STA's nonce */
 317         addr[3] = assoc_data->fils_nonces;
 318         len[3] = FILS_NONCE_LEN;
 319         /* The (Re)Association Response frame from the Capability Information
 320          * field to the FILS Session element (both inclusive).
 321          */
 322         addr[4] = capab;
 323         len[4] = encr - capab;
 324
 325         crypt_len = frame + *frame_len - encr;
 326         if (crypt_len < AES_BLOCK_SIZE) {
 327                 mlme_dbg(sdata,
 328                          "Not enough room for AES-SIV data after FILS Session element in (Re)Association Response frame from %pM",
 329                          mgmt->sa);
 330                 return -EINVAL;
 331         }
 332         res = aes_siv_decrypt(assoc_data->fils_kek, assoc_data->fils_kek_len,
 333                               encr, crypt_len, 5, addr, len, encr);
 334         if (res != 0) {
 335                 mlme_dbg(sdata,
 336                          "AES-SIV decryption of (Re)Association Response frame from %pM failed",
 337                          mgmt->sa);
 338                 return res;
 339         }
 340         *frame_len -= AES_BLOCK_SIZE;
 341         return 0;
 342 }