wusb: switch to cbcmac transform

The wusb code takes a very peculiar approach at implementing CBC-MAC,
by using plain CBC into a scratch buffer, and taking the output IV
as the MAC.

We can clean up this code substantially by switching to the cbcmac
shash, as exposed by the CCM template. To ensure that the module is
loaded on demand, add the cbcmac template name as a module alias.

Signed-off-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Ard Biesheuvel

crypto/ccm.c

@@ -1009,3 +1009,4 @@ MODULE_DESCRIPTION("Counter with CBC MAC");
 MODULE_ALIAS_CRYPTO("ccm_base");
 MODULE_ALIAS_CRYPTO("rfc4309");
 MODULE_ALIAS_CRYPTO("ccm");
+MODULE_ALIAS_CRYPTO("cbcmac");

drivers/usb/wusbcore/Kconfig

@@ -5,11 +5,9 @@
 config USB_WUSB
 	tristate "Enable Wireless USB extensions"
 	depends on UWB
-        select CRYPTO
-        select CRYPTO_BLKCIPHER
-        select CRYPTO_CBC
-        select CRYPTO_MANAGER
-        select CRYPTO_AES
+	select CRYPTO
+	select CRYPTO_AES
+	select CRYPTO_CCM
 	help
 	  Enable the host-side support for Wireless USB.
 

drivers/usb/wusbcore/crypto.c

@@ -31,6 +31,9 @@
  *             funneled through AES are...16 bytes in size!
  */
 
+#include <crypto/aes.h>
+#include <crypto/algapi.h>
+#include <crypto/hash.h>
 #include <crypto/skcipher.h>
 #include <linux/crypto.h>
 #include <linux/module.h>
@@ -109,16 +112,6 @@ struct aes_ccm_a {
 	__be16 counter;	/* Value of x */
 } __attribute__((packed));
 
-static void bytewise_xor(void *_bo, const void *_bi1, const void *_bi2,
-			 size_t size)
-{
-	u8 *bo = _bo;
-	const u8 *bi1 = _bi1, *bi2 = _bi2;
-	size_t itr;
-	for (itr = 0; itr < size; itr++)
-		bo[itr] = bi1[itr] ^ bi2[itr];
-}
-
 /* Scratch space for MAC calculations. */
 struct wusb_mac_scratch {
 	struct aes_ccm_b0 b0;
@@ -150,8 +143,7 @@ struct wusb_mac_scratch {
  * @a: ASCII string, 14 bytes long (I guess zero padded if needed;
  *     we use exactly 14 bytes).
  *
- * @b: data stream to be processed; cannot be a global or const local
- *     (will confuse the scatterlists)
+ * @b: data stream to be processed
  *
  * @blen: size of b...
  *
@@ -160,16 +152,10 @@ struct wusb_mac_scratch {
  * @key. We bytewise xor B0 with B1 (1) and AES-crypt that. Then we
  * take the payload and divide it in blocks (16 bytes), xor them with
  * the previous crypto result (16 bytes) and crypt it, repeat the next
- * block with the output of the previous one, rinse wash (I guess this
- * is what AES CBC mode means...but I truly have no idea). So we use
- * the CBC(AES) blkcipher, that does precisely that. The IV (Initial
+ * block with the output of the previous one, rinse wash. So we use
+ * the CBC-MAC(AES) shash, that does precisely that. The IV (Initial
  * Vector) is 16 bytes and is set to zero, so
  *
- * See rfc3610. Linux crypto has a CBC implementation, but the
- * documentation is scarce, to say the least, and the example code is
- * so intricated that is difficult to understand how things work. Most
- * of this is guess work -- bite me.
- *
  * (1) Created as 6.5 says, again, using as l(a) 'Blen + 14', and
  *     using the 14 bytes of @a to fill up
  *     b1.{mac_header,e0,security_reserved,padding}.
@@ -189,44 +175,24 @@ struct wusb_mac_scratch {
  * NOTE: blen is not aligned to a block size, we'll pad zeros, that's
  *       what sg[4] is for. Maybe there is a smarter way to do this.
  */
-static int wusb_ccm_mac(struct crypto_sync_skcipher *tfm_cbc,
-			struct crypto_cipher *tfm_aes,
+static int wusb_ccm_mac(struct crypto_shash *tfm_cbcmac,
 			struct wusb_mac_scratch *scratch,
 			void *mic,
 			const struct aes_ccm_nonce *n,
 			const struct aes_ccm_label *a, const void *b,
 			size_t blen)
 {
-	int result = 0;
-	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm_cbc);
-	struct scatterlist sg[4], sg_dst;
-	void *dst_buf;
-	size_t dst_size;
-	u8 *iv;
-	size_t zero_padding;
+	SHASH_DESC_ON_STACK(desc, tfm_cbcmac);
+	u8 iv[AES_BLOCK_SIZE];
 
 	/*
 	 * These checks should be compile time optimized out
 	 * ensure @a fills b1's mac_header and following fields
 	 */
-	WARN_ON(sizeof(*a) != sizeof(scratch->b1) - sizeof(scratch->b1.la));
-	WARN_ON(sizeof(scratch->b0) != sizeof(struct aes_ccm_block));
-	WARN_ON(sizeof(scratch->b1) != sizeof(struct aes_ccm_block));
-	WARN_ON(sizeof(scratch->ax) != sizeof(struct aes_ccm_block));
-
-	result = -ENOMEM;
-	zero_padding = blen % sizeof(struct aes_ccm_block);
-	if (zero_padding)
-		zero_padding = sizeof(struct aes_ccm_block) - zero_padding;
-	dst_size = blen + sizeof(scratch->b0) + sizeof(scratch->b1) +
-		zero_padding;
-	dst_buf = kzalloc(dst_size, GFP_KERNEL);
-	if (!dst_buf)
-		goto error_dst_buf;
-
-	iv = kzalloc(crypto_sync_skcipher_ivsize(tfm_cbc), GFP_KERNEL);
-	if (!iv)
-		goto error_iv;
+	BUILD_BUG_ON(sizeof(*a) != sizeof(scratch->b1) - sizeof(scratch->b1.la));
+	BUILD_BUG_ON(sizeof(scratch->b0) != sizeof(struct aes_ccm_block));
+	BUILD_BUG_ON(sizeof(scratch->b1) != sizeof(struct aes_ccm_block));
+	BUILD_BUG_ON(sizeof(scratch->ax) != sizeof(struct aes_ccm_block));
 
 	/* Setup B0 */
 	scratch->b0.flags = 0x59;	/* Format B0 */
@@ -243,46 +209,28 @@ static int wusb_ccm_mac(struct crypto_sync_skcipher *tfm_cbc,
 	scratch->b1.la = cpu_to_be16(blen + 14);
 	memcpy(&scratch->b1.mac_header, a, sizeof(*a));
 
-	sg_init_table(sg, ARRAY_SIZE(sg));
-	sg_set_buf(&sg[0], &scratch->b0, sizeof(scratch->b0));
-	sg_set_buf(&sg[1], &scratch->b1, sizeof(scratch->b1));
-	sg_set_buf(&sg[2], b, blen);
-	/* 0 if well behaved :) */
-	sg_set_page(&sg[3], ZERO_PAGE(0), zero_padding, 0);
-	sg_init_one(&sg_dst, dst_buf, dst_size);
-
-	skcipher_request_set_sync_tfm(req, tfm_cbc);
-	skcipher_request_set_callback(req, 0, NULL, NULL);
-	skcipher_request_set_crypt(req, sg, &sg_dst, dst_size, iv);
-	result = crypto_skcipher_encrypt(req);
-	skcipher_request_zero(req);
-	if (result < 0) {
-		printk(KERN_ERR "E: can't compute CBC-MAC tag (MIC): %d\n",
-		       result);
-		goto error_cbc_crypt;
-	}
+	desc->tfm = tfm_cbcmac;
+	crypto_shash_init(desc);
+	crypto_shash_update(desc, (u8 *)&scratch->b0, sizeof(scratch->b0) +
+						      sizeof(scratch->b1));
+	crypto_shash_finup(desc, b, blen, iv);
 
 	/* Now we crypt the MIC Tag (*iv) with Ax -- values per WUSB1.0[6.5]
 	 * The procedure is to AES crypt the A0 block and XOR the MIC
 	 * Tag against it; we only do the first 8 bytes and place it
 	 * directly in the destination buffer.
-	 *
-	 * POS Crypto API: size is assumed to be AES's block size.
-	 * Thanks for documenting it -- tip taken from airo.c
 	 */
 	scratch->ax.flags = 0x01;		/* as per WUSB 1.0 spec */
 	scratch->ax.ccm_nonce = *n;
 	scratch->ax.counter = 0;
-	crypto_cipher_encrypt_one(tfm_aes, (void *)&scratch->ax,
-				  (void *)&scratch->ax);
-	bytewise_xor(mic, &scratch->ax, iv, 8);
-	result = 8;
-error_cbc_crypt:
-	kfree(iv);
-error_iv:
-	kfree(dst_buf);
-error_dst_buf:
-	return result;
+
+	/* reuse the CBC-MAC transform to perform the single block encryption */
+	crypto_shash_digest(desc, (u8 *)&scratch->ax, sizeof(scratch->ax),
+			    (u8 *)&scratch->ax);
+
+	crypto_xor_cpy(mic, (u8 *)&scratch->ax, iv, 8);
+
+	return 8;
 }
 
 /*
@@ -298,61 +246,39 @@ ssize_t wusb_prf(void *out, size_t out_size,
 {
 	ssize_t result, bytes = 0, bitr;
 	struct aes_ccm_nonce n = *_n;
-	struct crypto_sync_skcipher *tfm_cbc;
-	struct crypto_cipher *tfm_aes;
-	struct wusb_mac_scratch *scratch;
+	struct crypto_shash *tfm_cbcmac;
+	struct wusb_mac_scratch scratch;
 	u64 sfn = 0;
 	__le64 sfn_le;
 
-	tfm_cbc = crypto_alloc_sync_skcipher("cbc(aes)", 0, 0);
-	if (IS_ERR(tfm_cbc)) {
-		result = PTR_ERR(tfm_cbc);
-		printk(KERN_ERR "E: can't load CBC(AES): %d\n", (int)result);
-		goto error_alloc_cbc;
-	}
-	result = crypto_sync_skcipher_setkey(tfm_cbc, key, 16);
-	if (result < 0) {
-		printk(KERN_ERR "E: can't set CBC key: %d\n", (int)result);
-		goto error_setkey_cbc;
+	tfm_cbcmac = crypto_alloc_shash("cbcmac(aes)", 0, 0);
+	if (IS_ERR(tfm_cbcmac)) {
+		result = PTR_ERR(tfm_cbcmac);
+		printk(KERN_ERR "E: can't load CBCMAC-AES: %d\n", (int)result);
+		goto error_alloc_cbcmac;
 	}
 
-	tfm_aes = crypto_alloc_cipher("aes", 0, 0);
-	if (IS_ERR(tfm_aes)) {
-		result = PTR_ERR(tfm_aes);
-		printk(KERN_ERR "E: can't load AES: %d\n", (int)result);
-		goto error_alloc_aes;
-	}
-	result = crypto_cipher_setkey(tfm_aes, key, 16);
+	result = crypto_shash_setkey(tfm_cbcmac, key, AES_BLOCK_SIZE);
 	if (result < 0) {
-		printk(KERN_ERR "E: can't set AES key: %d\n", (int)result);
-		goto error_setkey_aes;
-	}
-	scratch = kmalloc(sizeof(*scratch), GFP_KERNEL);
-	if (!scratch) {
-		result = -ENOMEM;
-		goto error_alloc_scratch;
+		printk(KERN_ERR "E: can't set CBCMAC-AES key: %d\n", (int)result);
+		goto error_setkey_cbcmac;
 	}
 
 	for (bitr = 0; bitr < (len + 63) / 64; bitr++) {
 		sfn_le = cpu_to_le64(sfn++);
 		memcpy(&n.sfn, &sfn_le, sizeof(n.sfn));	/* n.sfn++... */
-		result = wusb_ccm_mac(tfm_cbc, tfm_aes, scratch, out + bytes,
+		result = wusb_ccm_mac(tfm_cbcmac, &scratch, out + bytes,
 				      &n, a, b, blen);
 		if (result < 0)
 			goto error_ccm_mac;
 		bytes += result;
 	}
 	result = bytes;
 
-	kfree(scratch);
-error_alloc_scratch:
 error_ccm_mac:
-error_setkey_aes:
-	crypto_free_cipher(tfm_aes);
-error_alloc_aes:
-error_setkey_cbc:
-	crypto_free_sync_skcipher(tfm_cbc);
-error_alloc_cbc:
+error_setkey_cbcmac:
+	crypto_free_shash(tfm_cbcmac);
+error_alloc_cbcmac:
 	return result;
 }
 
@@ -377,12 +303,8 @@ static int wusb_oob_mic_verify(void)
 {
 	int result;
 	u8 mic[8];
-	/* WUSB1.0[A.2] test vectors
-	 *
-	 * Need to keep it in the local stack as GCC 4.1.3something
-	 * messes up and generates noise.
-	 */
-	struct usb_handshake stv_hsmic_hs = {
+	/* WUSB1.0[A.2] test vectors */
+	static const struct usb_handshake stv_hsmic_hs = {
 		.bMessageNumber = 2,
 		.bStatus 	= 00,
 		.tTKID 		= { 0x76, 0x98, 0x01 },
@@ -457,11 +379,8 @@ static int wusb_key_derive_verify(void)
 {
 	int result = 0;
 	struct wusb_keydvt_out keydvt_out;
-	/* These come from WUSB1.0[A.1] + 2006/12 errata
-	 * NOTE: can't make this const or global -- somehow it seems
-	 *       the scatterlists for crypto get confused and we get
-	 *       bad data. There is no doc on this... */
-	struct wusb_keydvt_in stv_keydvt_in_a1 = {
+	/* These come from WUSB1.0[A.1] + 2006/12 errata */
+	static const struct wusb_keydvt_in stv_keydvt_in_a1 = {
 		.hnonce = {
 			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
 			0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f