libipw_crypto_wep.c

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