[NETFILTER]: nf_conntrack: make l3proto->prepare() generic and renames it

The icmp[v6] l4proto modules parse headers in ICMP[v6] error to get tuple.
But they have to find the offset to transport protocol header before that.
Their processings are almost same as prepare() of l3proto modules.
This makes prepare() more generic to simplify icmp[v6] l4proto module
later.

Signed-off-by: Yasuyuki Kozakai <[e-mail]>
Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netfilter/ipv6/nf_conntrack_ipv6.h

···
 extern struct nf_conntrack_l4proto nf_conntrack_l4proto_udp6;
 extern struct nf_conntrack_l4proto nf_conntrack_l4proto_icmpv6;
 
-extern int nf_ct_ipv6_skip_exthdr(struct sk_buff *skb, int start,
+extern int nf_ct_ipv6_skip_exthdr(const struct sk_buff *skb, int start,
 				  u8 *nexthdrp, int len);
 
 extern int nf_ct_frag6_init(void);

include/net/netfilter/nf_conntrack_l3proto.h

···
 
 	/*
 	 * Called before tracking. 
-	 *	*dataoff: offset of protocol header (TCP, UDP,...) in *pskb
+	 *	*dataoff: offset of protocol header (TCP, UDP,...) in skb
 	 *	*protonum: protocol number
 	 */
-	int (*prepare)(struct sk_buff **pskb, unsigned int hooknum,
-		       unsigned int *dataoff, u_int8_t *protonum);
+	int (*get_l4proto)(const struct sk_buff *skb, unsigned int nhoff,
+			   unsigned int *dataoff, u_int8_t *protonum);
 
 	int (*tuple_to_nfattr)(struct sk_buff *skb,
 			       const struct nf_conntrack_tuple *t);

net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c

···
 	return skb;
 }
 
-static int
-ipv4_prepare(struct sk_buff **pskb, unsigned int hooknum, unsigned int *dataoff,
-	     u_int8_t *protonum)
+static int ipv4_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
+			    unsigned int *dataoff, u_int8_t *protonum)
 {
+	struct iphdr _iph, *iph;
+
+	iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
+	if (iph == NULL)
+		return -NF_DROP;
+
 	/* Never happen */
-	if (ip_hdr(*pskb)->frag_off & htons(IP_OFFSET)) {
+	if (iph->frag_off & htons(IP_OFFSET)) {
 		if (net_ratelimit()) {
-			printk(KERN_ERR "ipv4_prepare: Frag of proto %u (hook=%u)\n",
-			ip_hdr(*pskb)->protocol, hooknum);
+			printk(KERN_ERR "ipv4_get_l4proto: Frag of proto %u\n",
+			iph->protocol);
 		}
 		return -NF_DROP;
 	}
 
-	*dataoff = skb_network_offset(*pskb) + ip_hdrlen(*pskb);
-	*protonum = ip_hdr(*pskb)->protocol;
+	*dataoff = nhoff + (iph->ihl << 2);
+	*protonum = iph->protocol;
 
 	return NF_ACCEPT;
 }
···
 	.invert_tuple	 = ipv4_invert_tuple,
 	.print_tuple	 = ipv4_print_tuple,
 	.print_conntrack = ipv4_print_conntrack,
-	.prepare	 = ipv4_prepare,
+	.get_l4proto	 = ipv4_get_l4proto,
 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 	.tuple_to_nfattr = ipv4_tuple_to_nfattr,
 	.nfattr_to_tuple = ipv4_nfattr_to_tuple,

net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c

···
  *        - Note also special handling of AUTH header. Thanks to IPsec wizards.
  */
 
-int nf_ct_ipv6_skip_exthdr(struct sk_buff *skb, int start, u8 *nexthdrp,
+int nf_ct_ipv6_skip_exthdr(const struct sk_buff *skb, int start, u8 *nexthdrp,
 			   int len)
 {
 	u8 nexthdr = *nexthdrp;
···
 	return start;
 }
 
-static int
-ipv6_prepare(struct sk_buff **pskb, unsigned int hooknum, unsigned int *dataoff,
-	     u_int8_t *protonum)
+static int ipv6_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
+			    unsigned int *dataoff, u_int8_t *protonum)
 {
-	unsigned int extoff = (u8 *)(ipv6_hdr(*pskb) + 1) - (*pskb)->data;
-	unsigned char pnum = ipv6_hdr(*pskb)->nexthdr;
-	int protoff = nf_ct_ipv6_skip_exthdr(*pskb, extoff, &pnum,
-					     (*pskb)->len - extoff);
+	unsigned int extoff = nhoff + sizeof(struct ipv6hdr);
+	unsigned char pnum;
+	int protoff;
+
+	if (skb_copy_bits(skb, nhoff + offsetof(struct ipv6hdr, nexthdr),
+			  &pnum, sizeof(pnum)) != 0) {
+		pr_debug("ip6_conntrack_core: can't get nexthdr\n");
+		return -NF_ACCEPT;
+	}
+	protoff = nf_ct_ipv6_skip_exthdr(skb, extoff, &pnum, skb->len - extoff);
 	/*
-	 * (protoff == (*pskb)->len) mean that the packet doesn't have no data
+	 * (protoff == skb->len) mean that the packet doesn't have no data
 	 * except of IPv6 & ext headers. but it's tracked anyway. - YK
 	 */
-	if ((protoff < 0) || (protoff > (*pskb)->len)) {
+	if ((protoff < 0) || (protoff > skb->len)) {
 		pr_debug("ip6_conntrack_core: can't find proto in pkt\n");
 		return -NF_ACCEPT;
 	}
···
 	.invert_tuple		= ipv6_invert_tuple,
 	.print_tuple		= ipv6_print_tuple,
 	.print_conntrack	= ipv6_print_conntrack,
-	.prepare		= ipv6_prepare,
+	.get_l4proto		= ipv6_get_l4proto,
 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 	.tuple_to_nfattr	= ipv6_tuple_to_nfattr,
 	.nfattr_to_tuple	= ipv6_nfattr_to_tuple,

net/netfilter/nf_conntrack_core.c

···
 
 	/* rcu_read_lock()ed by nf_hook_slow */
 	l3proto = __nf_ct_l3proto_find((u_int16_t)pf);
-
-	if ((ret = l3proto->prepare(pskb, hooknum, &dataoff, &protonum)) <= 0) {
+	ret = l3proto->get_l4proto(*pskb, skb_network_offset(*pskb),
+				   &dataoff, &protonum);
+	if (ret <= 0) {
 		pr_debug("not prepared to track yet or error occured\n");
 		NF_CT_STAT_INC_ATOMIC(error);
 		NF_CT_STAT_INC_ATOMIC(invalid);

net/netfilter/nf_conntrack_l3proto_generic.c

···
 	return 0;
 }
 
-static int
-generic_prepare(struct sk_buff **pskb, unsigned int hooknum,
-		unsigned int *dataoff, u_int8_t *protonum)
+static int generic_get_l4proto(const struct sk_buff *skb, unsigned int nhoff,
+			       unsigned int *dataoff, u_int8_t *protonum)
 {
 	/* Never track !!! */
 	return -NF_ACCEPT;
···
 	.invert_tuple	 = generic_invert_tuple,
 	.print_tuple	 = generic_print_tuple,
 	.print_conntrack = generic_print_conntrack,
-	.prepare	 = generic_prepare,
+	.get_l4proto	 = generic_get_l4proto,
 };
 EXPORT_SYMBOL_GPL(nf_conntrack_l3proto_generic);