[PATCH 5.15.y 1/5] net: add a couple of helpers for iph tot_len

[Sasha Levin <sashal@kernel.org>]

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit 058a8f7f73aae1cc22b53fcefec031b9e391b54d ]

This patch adds three APIs to replace the iph->tot_len setting
and getting in all places where IPv4 BIG TCP packets may reach,
they will be used in the following patches.

Note that iph_totlen() will be used when iph is not in linear
data of the skb.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 8a7ed561671a ("net/sched: act_ct: fix sk_buff leak when the header checks reject a packet")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/ip.h  | 21 +++++++++++++++++++++
 include/net/route.h |  3 ---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/linux/ip.h b/include/linux/ip.h
index 3d9c6750af627..d11c25f5030a0 100644
--- a/include/linux/ip.h
+++ b/include/linux/ip.h
@@ -35,4 +35,25 @@ static inline unsigned int ip_transport_len(const struct sk_buff *skb)
 {
 	return ntohs(ip_hdr(skb)->tot_len) - skb_network_header_len(skb);
 }
+
+static inline unsigned int iph_totlen(const struct sk_buff *skb, const struct iphdr *iph)
+{
+	u32 len = ntohs(iph->tot_len);
+
+	return (len || !skb_is_gso(skb) || !skb_is_gso_tcp(skb)) ?
+	       len : skb->len - skb_network_offset(skb);
+}
+
+static inline unsigned int skb_ip_totlen(const struct sk_buff *skb)
+{
+	return iph_totlen(skb, ip_hdr(skb));
+}
+
+/* IPv4 datagram length is stored into 16bit field (tot_len) */
+#define IP_MAX_MTU	0xFFFFU
+
+static inline void iph_set_totlen(struct iphdr *iph, unsigned int len)
+{
+	iph->tot_len = len <= IP_MAX_MTU ? htons(len) : 0;
+}
 #endif	/* _LINUX_IP_H */
diff --git a/include/net/route.h b/include/net/route.h
index 39be632a9822d..717579169d573 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -35,9 +35,6 @@
 #include <linux/cache.h>
 #include <linux/security.h>
 
-/* IPv4 datagram length is stored into 16bit field (tot_len) */
-#define IP_MAX_MTU	0xFFFFU
-
 #define RTO_ONLINK	0x01
 
 #define RT_CONN_FLAGS(sk)   (RT_TOS(inet_sk(sk)->tos) | sock_flag(sk, SOCK_LOCALROUTE))
-- 
2.53.0