Subject: Re: minimum ICMPv6 message size vs. RPL's DIS

From: Werner Almesberger <[email-masked]>
Date: Thu, 25 Jul 2013 07:30:49 -0300

Hannes Frederic Sowa wrote:
> Hmm, maybe we should update the icmp header to something like

That would be quite clean. Is it okay to introduce new names
like that in a uapi/ header (uapi/linux/icmpv6.h) ?

> Hmm, there is a bug in this function, _hdr must not be a pointer.

Oh, I didn't even notice that. Very good catch !

So on 32 bit system, it would actually work even with "short"
ICMPv6 messages. Two wrongs sometimes do make a right :-)

I've attached a revised patch that, according to quick testing,
still works and doesn't break anything else.

Thanks,
- Werner

---------------------------------- cut here -----------------------------------

diff --git a/include/uapi/linux/icmpv6.h b/include/uapi/linux/icmpv6.h
index e0133c7..11eb5ff 100644
--- a/include/uapi/linux/icmpv6.h
+++ b/include/uapi/linux/icmpv6.h
@@ -5,11 +5,15 @@
 #include <asm/byteorder.h>
 
 struct icmp6hdr {
-
-	__u8		icmp6_type;
-	__u8		icmp6_code;
-	__sum16		icmp6_cksum;
-
+	struct icmp6hdr_head {
+		__u8		type;
+		__u8		code;
+		__sum16		cksum;
+	} icmpv6_head;
+
+#define	icmp6_type	icmpv6_head.type
+#define	icmp6_code	icmpv6_head.code
+#define	icmp6_cksum	icmpv6_head.cksum
 
 	union {
 		__be32			un_data32[1];
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index c45f7a5..99ab06f 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -108,14 +108,14 @@ found:
  */
 static int icmpv6_filter(const struct sock *sk, const struct sk_buff *skb)
 {
-	struct icmp6hdr *_hdr;
-	const struct icmp6hdr *hdr;
+	struct icmp6hdr_head _head;
+	const struct icmp6hdr_head *head;
 
-	hdr = skb_header_pointer(skb, skb_transport_offset(skb),
-				 sizeof(_hdr), &_hdr);
-	if (hdr) {
+	head = skb_header_pointer(skb, skb_transport_offset(skb),
+				  sizeof(_head), &_head);
+	if (head) {
 		const __u32 *data = &raw6_sk(sk)->filter.data[0];
-		unsigned int type = hdr->icmp6_type;
+		unsigned int type = head->type;
 
 		return (data[type >> 5] & (1U << (type & 31))) != 0;
 	}