xfrm: merge dstopt and routing hdroff functions

Both functions are very similar, so merge them into one.

The nexthdr is passed as argument to break the loop in the
ROUTING case, this is the only header type where slightly different
rules apply.

While at it, the merged function is realigned with
ip6_find_1stfragopt().  That function received bug fixes for an infinite
loop, but neither dstopt nor rh parsing functions (copy-pasted from
ip6_find_1stfragopt) were changed.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_output.c

@@ -78,24 +78,30 @@ static int xfrm4_transport_output(struct xfrm_state *x, struct sk_buff *skb)
 }
 
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
-static int mip6_destopt_offset(struct xfrm_state *x, struct sk_buff *skb,
-			       u8 **nexthdr)
+static int mip6_rthdr_offset(struct sk_buff *skb, u8 **nexthdr, int type)
 {
-	u16 offset = sizeof(struct ipv6hdr);
-	struct ipv6_opt_hdr *exthdr =
-				   (struct ipv6_opt_hdr *)(ipv6_hdr(skb) + 1);
 	const unsigned char *nh = skb_network_header(skb);
-	unsigned int packet_len = skb_tail_pointer(skb) -
-		skb_network_header(skb);
+	unsigned int offset = sizeof(struct ipv6hdr);
+	unsigned int packet_len;
 	int found_rhdr = 0;
 
+	packet_len = skb_tail_pointer(skb) - nh;
 	*nexthdr = &ipv6_hdr(skb)->nexthdr;
 
-	while (offset + 1 <= packet_len) {
+	while (offset <= packet_len) {
+		struct ipv6_opt_hdr *exthdr;
+
 		switch (**nexthdr) {
 		case NEXTHDR_HOP:
 			break;
 		case NEXTHDR_ROUTING:
+			if (type == IPPROTO_ROUTING && offset + 3 <= packet_len) {
+				struct ipv6_rt_hdr *rt;
+
+				rt = (struct ipv6_rt_hdr *)(nh + offset);
+				if (rt->type != 0)
+					return offset;
+			}
 			found_rhdr = 1;
 			break;
 		case NEXTHDR_DEST:
@@ -116,59 +122,18 @@ static int mip6_destopt_offset(struct xfrm_state *x, struct sk_buff *skb,
 			return offset;
 		}
 
+		if (offset + sizeof(struct ipv6_opt_hdr) > packet_len)
+			return -EINVAL;
+
+		exthdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) +
+						 offset);
 		offset += ipv6_optlen(exthdr);
+		if (offset > IPV6_MAXPLEN)
+			return -EINVAL;
 		*nexthdr = &exthdr->nexthdr;
-		exthdr = (struct ipv6_opt_hdr *)(nh + offset);
 	}
 
-	return offset;
-}
-
-static int mip6_rthdr_offset(struct xfrm_state *x, struct sk_buff *skb,
-			     u8 **nexthdr)
-{
-	u16 offset = sizeof(struct ipv6hdr);
-	struct ipv6_opt_hdr *exthdr =
-				   (struct ipv6_opt_hdr *)(ipv6_hdr(skb) + 1);
-	const unsigned char *nh = skb_network_header(skb);
-	unsigned int packet_len = skb_tail_pointer(skb) -
-		skb_network_header(skb);
-	int found_rhdr = 0;
-
-	*nexthdr = &ipv6_hdr(skb)->nexthdr;
-
-	while (offset + 1 <= packet_len) {
-		switch (**nexthdr) {
-		case NEXTHDR_HOP:
-			break;
-		case NEXTHDR_ROUTING:
-			if (offset + 3 <= packet_len) {
-				struct ipv6_rt_hdr *rt;
-
-				rt = (struct ipv6_rt_hdr *)(nh + offset);
-				if (rt->type != 0)
-					return offset;
-			}
-			found_rhdr = 1;
-			break;
-		case NEXTHDR_DEST:
-			if (ipv6_find_tlv(skb, offset, IPV6_TLV_HAO) >= 0)
-				return offset;
-
-			if (found_rhdr)
-				return offset;
-
-			break;
-		default:
-			return offset;
-		}
-
-		offset += ipv6_optlen(exthdr);
-		*nexthdr = &exthdr->nexthdr;
-		exthdr = (struct ipv6_opt_hdr *)(nh + offset);
-	}
-
-	return offset;
+	return -EINVAL;
 }
 #endif
 
@@ -177,9 +142,8 @@ static int xfrm6_hdr_offset(struct xfrm_state *x, struct sk_buff *skb, u8 **prev
 	switch (x->type->proto) {
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
 	case IPPROTO_DSTOPTS:
-		return mip6_destopt_offset(x, skb, prevhdr);
 	case IPPROTO_ROUTING:
-		return mip6_rthdr_offset(x, skb, prevhdr);
+		return mip6_rthdr_offset(skb, prevhdr, x->type->proto);
 #endif
 	default:
 		break;