net/wireless/lib80211_crypt_wep.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * lib80211 crypt: host-based WEP encryption implementation for lib80211
   4  *
   5  * Copyright (c) 2002-2004, Jouni Malinen <j@w1.fi>
   6  * Copyright (c) 2008, John W. Linville <linville@tuxdriver.com>
   7  */
   8
   9 #include <linux/err.h>
  10 #include <linux/fips.h>
  11 #include <linux/module.h>
  12 #include <linux/init.h>
  13 #include <linux/slab.h>
  14 #include <linux/random.h>
  15 #include <linux/scatterlist.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/mm.h>
  18 #include <asm/string.h>
  19
  20 #include <net/lib80211.h>
  21
  22 #include <crypto/arc4.h>
  23 #include <linux/crc32.h>
  24
  25 MODULE_AUTHOR("Jouni Malinen");
  26 MODULE_DESCRIPTION("lib80211 crypt: WEP");
  27 MODULE_LICENSE("GPL");
  28
  29 struct lib80211_wep_data {
  30         u32 iv;
  31 #define WEP_KEY_LEN 13
  32         u8 key[WEP_KEY_LEN + 1];
  33         u8 key_len;
  34         u8 key_idx;
  35         struct arc4_ctx tx_ctx;
  36         struct arc4_ctx rx_ctx;
  37 };
  38
  39 static void *lib80211_wep_init(int keyidx)
  40 {
  41         struct lib80211_wep_data *priv;
  42
  43         if (fips_enabled)
  44                 return NULL;
  45
  46         priv = kzalloc(sizeof(*priv), GFP_ATOMIC);
  47         if (priv == NULL)
  48                 return NULL;
  49         priv->key_idx = keyidx;
  50
  51         /* start WEP IV from a random value */
  52         get_random_bytes(&priv->iv, 4);
  53
  54         return priv;
  55 }
  56
  57 static void lib80211_wep_deinit(void *priv)
  58 {
  59         kfree_sensitive(priv);
  60 }
  61
  62 /* Add WEP IV/key info to a frame that has at least 4 bytes of headroom */
  63 static int lib80211_wep_build_iv(struct sk_buff *skb, int hdr_len,
  64                                u8 *key, int keylen, void *priv)
  65 {
  66         struct lib80211_wep_data *wep = priv;
  67         u32 klen;
  68         u8 *pos;
  69
  70         if (skb_headroom(skb) < 4 || skb->len < hdr_len)
  71                 return -1;
  72
  73         pos = skb_push(skb, 4);
  74         memmove(pos, pos + 4, hdr_len);
  75         pos += hdr_len;
  76
  77         klen = 3 + wep->key_len;
  78
  79         wep->iv++;
  80
  81         /* Fluhrer, Mantin, and Shamir have reported weaknesses in the key
  82          * scheduling algorithm of RC4. At least IVs (KeyByte + 3, 0xff, N)
  83          * can be used to speedup attacks, so avoid using them. */
  84         if ((wep->iv & 0xff00) == 0xff00) {
  85                 u8 B = (wep->iv >> 16) & 0xff;
  86                 if (B >= 3 && B < klen)
  87                         wep->iv += 0x0100;
  88         }
  89
  90         /* Prepend 24-bit IV to RC4 key and TX frame */
  91         *pos++ = (wep->iv >> 16) & 0xff;
  92         *pos++ = (wep->iv >> 8) & 0xff;
  93         *pos++ = wep->iv & 0xff;
  94         *pos++ = wep->key_idx << 6;
  95
  96         return 0;
  97 }
  98
  99 /* Perform WEP encryption on given skb that has at least 4 bytes of headroom
 100  * for IV and 4 bytes of tailroom for ICV. Both IV and ICV will be transmitted,
 101  * so the payload length increases with 8 bytes.
 102  *
 103  * WEP frame payload: IV + TX key idx, RC4(data), ICV = RC4(CRC32(data))
 104  */
 105 static int lib80211_wep_encrypt(struct sk_buff *skb, int hdr_len, void *priv)
 106 {
 107         struct lib80211_wep_data *wep = priv;
 108         u32 crc, klen, len;
 109         u8 *pos, *icv;
 110         u8 key[WEP_KEY_LEN + 3];
 111
 112         /* other checks are in lib80211_wep_build_iv */
 113         if (skb_tailroom(skb) < 4)
 114                 return -1;
 115
 116         /* add the IV to the frame */
 117         if (lib80211_wep_build_iv(skb, hdr_len, NULL, 0, priv))
 118                 return -1;
 119
 120         /* Copy the IV into the first 3 bytes of the key */
 121         skb_copy_from_linear_data_offset(skb, hdr_len, key, 3);
 122
 123         /* Copy rest of the WEP key (the secret part) */
 124         memcpy(key + 3, wep->key, wep->key_len);
 125
 126         len = skb->len - hdr_len - 4;
 127         pos = skb->data + hdr_len + 4;
 128         klen = 3 + wep->key_len;
 129
 130         /* Append little-endian CRC32 over only the data and encrypt it to produce ICV */
 131         crc = ~crc32_le(~0, pos, len);
 132         icv = skb_put(skb, 4);
 133         icv[0] = crc;
 134         icv[1] = crc >> 8;
 135         icv[2] = crc >> 16;
 136         icv[3] = crc >> 24;
 137
 138         arc4_setkey(&wep->tx_ctx, key, klen);
 139         arc4_crypt(&wep->tx_ctx, pos, pos, len + 4);
 140
 141         return 0;
 142 }
 143
 144 /* Perform WEP decryption on given buffer. Buffer includes whole WEP part of
 145  * the frame: IV (4 bytes), encrypted payload (including SNAP header),
 146  * ICV (4 bytes). len includes both IV and ICV.
 147  *
 148  * Returns 0 if frame was decrypted successfully and ICV was correct and -1 on
 149  * failure. If frame is OK, IV and ICV will be removed.
 150  */
 151 static int lib80211_wep_decrypt(struct sk_buff *skb, int hdr_len, void *priv)
 152 {
 153         struct lib80211_wep_data *wep = priv;
 154         u32 crc, klen, plen;
 155         u8 key[WEP_KEY_LEN + 3];
 156         u8 keyidx, *pos, icv[4];
 157
 158         if (skb->len < hdr_len + 8)
 159                 return -1;
 160
 161         pos = skb->data + hdr_len;
 162         key[0] = *pos++;
 163         key[1] = *pos++;
 164         key[2] = *pos++;
 165         keyidx = *pos++ >> 6;
 166         if (keyidx != wep->key_idx)
 167                 return -1;
 168
 169         klen = 3 + wep->key_len;
 170
 171         /* Copy rest of the WEP key (the secret part) */
 172         memcpy(key + 3, wep->key, wep->key_len);
 173
 174         /* Apply RC4 to data and compute CRC32 over decrypted data */
 175         plen = skb->len - hdr_len - 8;
 176
 177         arc4_setkey(&wep->rx_ctx, key, klen);
 178         arc4_crypt(&wep->rx_ctx, pos, pos, plen + 4);
 179
 180         crc = ~crc32_le(~0, pos, plen);
 181         icv[0] = crc;
 182         icv[1] = crc >> 8;
 183         icv[2] = crc >> 16;
 184         icv[3] = crc >> 24;
 185         if (memcmp(icv, pos + plen, 4) != 0) {
 186                 /* ICV mismatch - drop frame */
 187                 return -2;
 188         }
 189
 190         /* Remove IV and ICV */
 191         memmove(skb->data + 4, skb->data, hdr_len);
 192         skb_pull(skb, 4);
 193         skb_trim(skb, skb->len - 4);
 194
 195         return 0;
 196 }
 197
 198 static int lib80211_wep_set_key(void *key, int len, u8 * seq, void *priv)
 199 {
 200         struct lib80211_wep_data *wep = priv;
 201
 202         if (len < 0 || len > WEP_KEY_LEN)
 203                 return -1;
 204
 205         memcpy(wep->key, key, len);
 206         wep->key_len = len;
 207
 208         return 0;
 209 }
 210
 211 static int lib80211_wep_get_key(void *key, int len, u8 * seq, void *priv)
 212 {
 213         struct lib80211_wep_data *wep = priv;
 214
 215         if (len < wep->key_len)
 216                 return -1;
 217
 218         memcpy(key, wep->key, wep->key_len);
 219
 220         return wep->key_len;
 221 }
 222
 223 static void lib80211_wep_print_stats(struct seq_file *m, void *priv)
 224 {
 225         struct lib80211_wep_data *wep = priv;
 226         seq_printf(m, "key[%d] alg=WEP len=%d\n", wep->key_idx, wep->key_len);
 227 }
 228
 229 static struct lib80211_crypto_ops lib80211_crypt_wep = {
 230         .name = "WEP",
 231         .init = lib80211_wep_init,
 232         .deinit = lib80211_wep_deinit,
 233         .encrypt_mpdu = lib80211_wep_encrypt,
 234         .decrypt_mpdu = lib80211_wep_decrypt,
 235         .encrypt_msdu = NULL,
 236         .decrypt_msdu = NULL,
 237         .set_key = lib80211_wep_set_key,
 238         .get_key = lib80211_wep_get_key,
 239         .print_stats = lib80211_wep_print_stats,
 240         .extra_mpdu_prefix_len = 4,     /* IV */
 241         .extra_mpdu_postfix_len = 4,    /* ICV */
 242         .owner = THIS_MODULE,
 243 };
 244
 245 static int __init lib80211_crypto_wep_init(void)
 246 {
 247         return lib80211_register_crypto_ops(&lib80211_crypt_wep);
 248 }
 249
 250 static void __exit lib80211_crypto_wep_exit(void)
 251 {
 252         lib80211_unregister_crypto_ops(&lib80211_crypt_wep);
 253 }
 254
 255 module_init(lib80211_crypto_wep_init);
 256 module_exit(lib80211_crypto_wep_exit);