6lowpan: lowpan_uncompress_addr with address_mode

This patch drops the pre and postcount calculation from the
lowpan_uncompress_addr function.We use instead a switch/case
over address_mode value. The original implementation has several
bugs in this function and it was hard to decrypt how it works.
To make it maintainable and fix these bugs this patch basically
reimplements lowpan_uncompress_addr from scratch.

A list of bugs we found in the current implementation:

1) Properly support uncompression of short-address based IPv6 addresses
   (instead of basically copying garbage)

2) Fix use and uncompression of long-addresses based IPv6 addresses

3) Add missing ff:fe00 in the case of SAM/DAM = 2 and M = 0

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Werner Almesberger <werner@almesberger.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -67,30 +67,6 @@ static const u8 lowpan_ttl_values[] = {0, 1, 64, 255};
 
 static LIST_HEAD(lowpan_devices);
 
-/*
- * Uncompression of linklocal:
- *   0 -> 16 bytes from packet
- *   1 -> 2  bytes from prefix - bunch of zeroes and 8 from packet
- *   2 -> 2  bytes from prefix - zeroes + 2 from packet
- *   3 -> 2  bytes from prefix - infer 8 bytes from lladdr
- *
- *  NOTE: => the uncompress function does change 0xf to 0x10
- *  NOTE: 0x00 => no-autoconfig => unspecified
- */
-static const u8 lowpan_unc_llconf[] = {0x0f, 0x28, 0x22, 0x20};
-
-/*
- * Uncompression of ctx-based:
- *   0 -> 0 bits  from packet [unspecified / reserved]
- *   1 -> 8 bytes from prefix - bunch of zeroes and 8 from packet
- *   2 -> 8 bytes from prefix - zeroes + 2 from packet
- *   3 -> 8 bytes from prefix - infer 8 bytes from lladdr
- */
-static const u8 lowpan_unc_ctxconf[] = {0x00, 0x88, 0x82, 0x80};
-
-/* Link local prefix */
-static const u8 lowpan_llprefix[] = {0xfe, 0x80};
-
 /* private device info */
 struct lowpan_dev_info {
 	struct net_device	*real_dev; /* real WPAN device ptr */
@@ -182,51 +158,86 @@ lowpan_compress_addr_64(u8 **hc06_ptr, u8 shift, const struct in6_addr *ipaddr,
 	return rol8(val, shift);
 }
 
-static void
-lowpan_uip_ds6_set_addr_iid(struct in6_addr *ipaddr, unsigned char *lladdr)
-{
-	memcpy(&ipaddr->s6_addr[8], lladdr, IEEE802154_ADDR_LEN);
-	/* second bit-flip (Universe/Local) is done according RFC2464 */
-	ipaddr->s6_addr[8] ^= 0x02;
-}
-
 /*
- * Uncompress addresses based on a prefix and a postfix with zeroes in
- * between. If the postfix is zero in length it will use the link address
- * to configure the IP address (autoconf style).
- * pref_post_count takes a byte where the first nibble specify prefix count
- * and the second postfix count (NOTE: 15/0xf => 16 bytes copy).
+ * Uncompress address function for source and
+ * destination address(non-multicast).
+ *
+ * address_mode is sam value or dam value.
  */
 static int
-lowpan_uncompress_addr(struct sk_buff *skb, struct in6_addr *ipaddr,
-	u8 const *prefix, u8 pref_post_count, unsigned char *lladdr)
+lowpan_uncompress_addr(struct sk_buff *skb,
+		struct in6_addr *ipaddr,
+		const u8 address_mode,
+		const struct ieee802154_addr *lladdr)
 {
-	u8 prefcount = pref_post_count >> 4;
-	u8 postcount = pref_post_count & 0x0f;
-
-	/* full nibble 15 => 16 */
-	prefcount = (prefcount == 15 ? 16 : prefcount);
-	postcount = (postcount == 15 ? 16 : postcount);
-
-	if (lladdr)
-		lowpan_raw_dump_inline(__func__, "linklocal address",
-						lladdr,	IEEE802154_ADDR_LEN);
-	if (prefcount > 0)
-		memcpy(ipaddr, prefix, prefcount);
-
-	if (postcount > 0) {
-		memcpy(&ipaddr->s6_addr[16 - postcount], skb->data, postcount);
-		skb_pull(skb, postcount);
-	} else if (prefcount > 0) {
-		if (lladdr == NULL)
+	bool fail;
+
+	switch (address_mode) {
+	case LOWPAN_IPHC_ADDR_00:
+		/* for global link addresses */
+		fail = lowpan_fetch_skb(skb, ipaddr->s6_addr, 16);
+		break;
+	case LOWPAN_IPHC_ADDR_01:
+		/* fe:80::XXXX:XXXX:XXXX:XXXX */
+		ipaddr->s6_addr[0] = 0xFE;
+		ipaddr->s6_addr[1] = 0x80;
+		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[8], 8);
+		break;
+	case LOWPAN_IPHC_ADDR_02:
+		/* fe:80::ff:fe00:XXXX */
+		ipaddr->s6_addr[0] = 0xFE;
+		ipaddr->s6_addr[1] = 0x80;
+		ipaddr->s6_addr[11] = 0xFF;
+		ipaddr->s6_addr[12] = 0xFE;
+		fail = lowpan_fetch_skb(skb, &ipaddr->s6_addr[14], 2);
+		break;
+	case LOWPAN_IPHC_ADDR_03:
+		fail = false;
+		switch (lladdr->addr_type) {
+		case IEEE802154_ADDR_LONG:
+			/* fe:80::XXXX:XXXX:XXXX:XXXX
+			 *        \_________________/
+			 *              hwaddr
+			 */
+			ipaddr->s6_addr[0] = 0xFE;
+			ipaddr->s6_addr[1] = 0x80;
+			memcpy(&ipaddr->s6_addr[8], lladdr->hwaddr,
+					IEEE802154_ADDR_LEN);
+			/* second bit-flip (Universe/Local)
+			 * is done according RFC2464
+			 */
+			ipaddr->s6_addr[8] ^= 0x02;
+			break;
+		case IEEE802154_ADDR_SHORT:
+			/* fe:80::ff:fe00:XXXX
+			 *		  \__/
+			 *	       short_addr
+			 *
+			 * Universe/Local bit is zero.
+			 */
+			ipaddr->s6_addr[0] = 0xFE;
+			ipaddr->s6_addr[1] = 0x80;
+			ipaddr->s6_addr[11] = 0xFF;
+			ipaddr->s6_addr[12] = 0xFE;
+			ipaddr->s6_addr16[7] = htons(lladdr->short_addr);
+			break;
+		default:
+			pr_debug("Invalid addr_type set\n");
 			return -EINVAL;
+		}
+		break;
+	default:
+		pr_debug("Invalid address mode value: 0x%x\n", address_mode);
+		return -EINVAL;
+	}
 
-		/* no IID based configuration if no prefix and no data */
-		lowpan_uip_ds6_set_addr_iid(ipaddr, lladdr);
+	if (fail) {
+		pr_debug("Failed to fetch skb data\n");
+		return -EIO;
 	}
 
-	pr_debug("uncompressing %d + %d => ", prefcount, postcount);
-	lowpan_raw_dump_inline(NULL, NULL, ipaddr->s6_addr, 16);
+	lowpan_raw_dump_inline(NULL, "Reconstructed ipv6 addr is:\n",
+			ipaddr->s6_addr, 16);
 
 	return 0;
 }
@@ -775,7 +786,7 @@ lowpan_process_data(struct sk_buff *skb)
 {
 	struct ipv6hdr hdr = {};
 	u8 tmp, iphc0, iphc1, num_context = 0;
-	u8 *_saddr, *_daddr;
+	const struct ieee802154_addr *_saddr, *_daddr;
 	int err;
 
 	lowpan_raw_dump_table(__func__, "raw skb data dump", skb->data,
@@ -878,8 +889,8 @@ lowpan_process_data(struct sk_buff *skb)
 	if (lowpan_fetch_skb_u8(skb, &iphc1))
 		goto drop;
 
-	_saddr = mac_cb(skb)->sa.hwaddr;
-	_daddr = mac_cb(skb)->da.hwaddr;
+	_saddr = &mac_cb(skb)->sa;
+	_daddr = &mac_cb(skb)->da;
 
 	pr_debug("iphc0 = %02x, iphc1 = %02x\n", iphc0, iphc1);
 
@@ -961,8 +972,7 @@ lowpan_process_data(struct sk_buff *skb)
 
 	/* Source address uncompression */
 	pr_debug("source address stateless compression\n");
-	err = lowpan_uncompress_addr(skb, &hdr.saddr, lowpan_llprefix,
-				lowpan_unc_llconf[tmp], skb->data);
+	err = lowpan_uncompress_addr(skb, &hdr.saddr, tmp, _saddr);
 	if (err)
 		goto drop;
 
@@ -982,8 +992,7 @@ lowpan_process_data(struct sk_buff *skb)
 		}
 	} else {
 		pr_debug("dest: stateless compression\n");
-		err = lowpan_uncompress_addr(skb, &hdr.daddr, lowpan_llprefix,
-				lowpan_unc_llconf[tmp], skb->data);
+		err = lowpan_uncompress_addr(skb, &hdr.daddr, tmp, _daddr);
 		if (err)
 			goto drop;
 	}

net/ieee802154/6lowpan.h

@@ -193,10 +193,12 @@
 /* Values of fields within the IPHC encoding second byte */
 #define LOWPAN_IPHC_CID		0x80
 
+#define LOWPAN_IPHC_ADDR_00	0x00
+#define LOWPAN_IPHC_ADDR_01	0x01
+#define LOWPAN_IPHC_ADDR_02	0x02
+#define LOWPAN_IPHC_ADDR_03	0x03
+
 #define LOWPAN_IPHC_SAC		0x40
-#define LOWPAN_IPHC_SAM_00	0x00
-#define LOWPAN_IPHC_SAM_01	0x10
-#define LOWPAN_IPHC_SAM_10	0x20
 #define LOWPAN_IPHC_SAM		0x30
 
 #define LOWPAN_IPHC_SAM_BIT	4