bonding: fix ICMPv6 header handling when receiving IPv6 messages

Currently, we get icmp6hdr via function icmp6_hdr(), which needs the skb
transport header to be set first. But there is no rule to ask driver set
transport header before netif_receive_skb() and bond_handle_frame(). So
we will not able to get correct icmp6hdr on some drivers.

Fix this by using skb_header_pointer to get the IPv6 and ICMPV6 headers.

Reported-by: Liang Li <liali@redhat.com>
Fixes: 4e24be0 ("bonding: add new parameter ns_targets")
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Link: https://lore.kernel.org/r/20221118034353.1736727-1-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/bonding/bond_main.c

@@ -3231,16 +3231,23 @@ static int bond_na_rcv(const struct sk_buff *skb, struct bonding *bond,
 		       struct slave *slave)
 {
 	struct slave *curr_active_slave, *curr_arp_slave;
-	struct icmp6hdr *hdr = icmp6_hdr(skb);
 	struct in6_addr *saddr, *daddr;
+	struct {
+		struct ipv6hdr ip6;
+		struct icmp6hdr icmp6;
+	} *combined, _combined;
 
 	if (skb->pkt_type == PACKET_OTHERHOST ||
-	    skb->pkt_type == PACKET_LOOPBACK ||
-	    hdr->icmp6_type != NDISC_NEIGHBOUR_ADVERTISEMENT)
+	    skb->pkt_type == PACKET_LOOPBACK)
+		goto out;
+
+	combined = skb_header_pointer(skb, 0, sizeof(_combined), &_combined);
+	if (!combined || combined->ip6.nexthdr != NEXTHDR_ICMP ||
+	    combined->icmp6.icmp6_type != NDISC_NEIGHBOUR_ADVERTISEMENT)
 		goto out;
 
-	saddr = &ipv6_hdr(skb)->saddr;
-	daddr = &ipv6_hdr(skb)->daddr;
+	saddr = &combined->ip6.saddr;
+	daddr = &combined->ip6.saddr;
 
 	slave_dbg(bond->dev, slave->dev, "%s: %s/%d av %d sv %d sip %pI6c tip %pI6c\n",
 		  __func__, slave->dev->name, bond_slave_state(slave),