ipv6: do not use skb_header_pointer() in icmpv6_filter()

Prefer pskb_may_pull() to avoid a stack canary in raw6_local_deliver().

Note: skb->head can change, hence we reload ip6h pointer in
ipv6_raw_deliver()

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-86 (-86)
Function                                     old     new   delta
raw6_local_deliver                           780     694     -86
Total: Before=24889784, After=24889698, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260205211909.4115285-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/ipv6/raw.c

@@ -90,23 +90,24 @@ EXPORT_SYMBOL_GPL(raw_v6_match);
  *	0 - deliver
  *	1 - block
  */
-static int icmpv6_filter(const struct sock *sk, const struct sk_buff *skb)
+static int icmpv6_filter(const struct sock *sk, struct sk_buff *skb)
 {
-	struct icmp6hdr _hdr;
 	const struct icmp6hdr *hdr;
+	const __u32 *data;
+	unsigned int type;
 
 	/* We require only the four bytes of the ICMPv6 header, not any
 	 * additional bytes of message body in "struct icmp6hdr".
 	 */
-	hdr = skb_header_pointer(skb, skb_transport_offset(skb),
-				 ICMPV6_HDRLEN, &_hdr);
-	if (hdr) {
-		const __u32 *data = &raw6_sk(sk)->filter.data[0];
-		unsigned int type = hdr->icmp6_type;
+	if (!pskb_may_pull(skb, ICMPV6_HDRLEN))
+		return 1;
 
-		return (data[type >> 5] & (1U << (type & 31))) != 0;
-	}
-	return 1;
+	hdr = (struct icmp6hdr *)skb->data;
+	type = hdr->icmp6_type;
+
+	data = &raw6_sk(sk)->filter.data[0];
+
+	return (data[type >> 5] & (1U << (type & 31))) != 0;
 }
 
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
@@ -141,23 +142,21 @@ EXPORT_SYMBOL(rawv6_mh_filter_unregister);
 static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 {
 	struct net *net = dev_net(skb->dev);
-	const struct in6_addr *saddr;
-	const struct in6_addr *daddr;
+	const struct ipv6hdr *ip6h;
 	struct hlist_head *hlist;
-	struct sock *sk;
 	bool delivered = false;
+	struct sock *sk;
 	__u8 hash;
 
-	saddr = &ipv6_hdr(skb)->saddr;
-	daddr = saddr + 1;
+	ip6h = ipv6_hdr(skb);
 
 	hash = raw_hashfunc(net, nexthdr);
 	hlist = &raw_v6_hashinfo.ht[hash];
 	rcu_read_lock();
 	sk_for_each_rcu(sk, hlist) {
 		int filtered;
 
-		if (!raw_v6_match(net, sk, nexthdr, daddr, saddr,
+		if (!raw_v6_match(net, sk, nexthdr, &ip6h->daddr, &ip6h->saddr,
 				  inet6_iif(skb), inet6_sdif(skb)))
 			continue;
 
@@ -171,6 +170,7 @@ static bool ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
 		switch (nexthdr) {
 		case IPPROTO_ICMPV6:
 			filtered = icmpv6_filter(sk, skb);
+			ip6h = ipv6_hdr(skb);
 			break;
 
 #if IS_ENABLED(CONFIG_IPV6_MIP6)