netfilter: use skb_ip_totlen and iph_totlen

There are also quite some places in netfilter that may process IPv4 TCP
GSO packets, we need to replace them too.

In length_mt(), we have to use u_int32_t/int to accept skb_ip_totlen()
return value, otherwise it may overflow and mismatch. This change will
also help us add selftest for IPv4 BIG TCP in the following patch.

Note that we don't need to replace the one in tcpmss_tg4(), as it will
return if there is data after tcphdr in tcpmss_mangle_packet(). The
same in mangle_contents() in nf_nat_helper.c, it returns false when
skb->len + extra > 65535 in enlarge_skb().

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/netfilter/nf_tables_ipv4.h

@@ -29,7 +29,7 @@ static inline int __nft_set_pktinfo_ipv4_validate(struct nft_pktinfo *pkt)
 	if (iph->ihl < 5 || iph->version != 4)
 		return -1;
 
-	len = ntohs(iph->tot_len);
+	len = iph_totlen(pkt->skb, iph);
 	thoff = iph->ihl * 4;
 	if (pkt->skb->len < len)
 		return -1;
@@ -64,7 +64,7 @@ static inline int nft_set_pktinfo_ipv4_ingress(struct nft_pktinfo *pkt)
 	if (iph->ihl < 5 || iph->version != 4)
 		goto inhdr_error;
 
-	len = ntohs(iph->tot_len);
+	len = iph_totlen(pkt->skb, iph);
 	thoff = iph->ihl * 4;
 	if (pkt->skb->len < len) {
 		__IP_INC_STATS(nft_net(pkt), IPSTATS_MIB_INTRUNCATEDPKTS);

net/netfilter/ipvs/ip_vs_xmit.c

@@ -994,7 +994,7 @@ ip_vs_prepare_tunneled_skb(struct sk_buff *skb, int skb_af,
 		old_dsfield = ipv4_get_dsfield(old_iph);
 		*ttl = old_iph->ttl;
 		if (payload_len)
-			*payload_len = ntohs(old_iph->tot_len);
+			*payload_len = skb_ip_totlen(skb);
 	}
 
 	/* Implement full-functionality option for ECN encapsulation */

net/netfilter/nf_log_syslog.c

@@ -322,7 +322,7 @@ dump_ipv4_packet(struct net *net, struct nf_log_buf *m,
 
 	/* Max length: 46 "LEN=65535 TOS=0xFF PREC=0xFF TTL=255 ID=65535 " */
 	nf_log_buf_add(m, "LEN=%u TOS=0x%02X PREC=0x%02X TTL=%u ID=%u ",
-		       ntohs(ih->tot_len), ih->tos & IPTOS_TOS_MASK,
+		       iph_totlen(skb, ih), ih->tos & IPTOS_TOS_MASK,
 		       ih->tos & IPTOS_PREC_MASK, ih->ttl, ntohs(ih->id));
 
 	/* Max length: 6 "CE DF MF " */

net/netfilter/xt_length.c

@@ -21,7 +21,7 @@ static bool
 length_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	const struct xt_length_info *info = par->matchinfo;
-	u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
+	u32 pktlen = skb_ip_totlen(skb);
 
 	return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
 }