inet: constify ip headers and in6_addr

Add const qualifiers to structs iphdr, ipv6hdr and in6_addr pointers
where possible, to make code intention more obvious.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

19 files changed, 57 insertions, 55 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 807d83c02ef6..cae75ef21fea 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1186,7 +1186,7 @@ EXPORT_SYMBOL(inet_sk_rebuild_header);
 
 static int inet_gso_send_check(struct sk_buff *skb)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	const struct net_protocol *ops;
 	int proto;
 	int ihl;
@@ -1293,7 +1293,7 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
 	const struct net_protocol *ops;
 	struct sk_buff **pp = NULL;
 	struct sk_buff *p;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	unsigned int hlen;
 	unsigned int off;
 	unsigned int id;
diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index 4286fd3cc0e2..c1f4154552fc 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -73,7 +73,7 @@ static inline struct scatterlist *ah_req_sg(struct crypto_ahash *ahash,
  * into IP header for icv calculation. Options are already checked
  * for validity, so paranoia is not required. */
 
-static int ip_clear_mutable_options(struct iphdr *iph, __be32 *daddr)
+static int ip_clear_mutable_options(const struct iphdr *iph, __be32 *daddr)
 {
 	unsigned char * optptr = (unsigned char*)(iph+1);
 	int  l = iph->ihl*4 - sizeof(struct iphdr);
@@ -396,7 +396,7 @@ out:
 static void ah4_err(struct sk_buff *skb, u32 info)
 {
 	struct net *net = dev_net(skb->dev);
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	struct ip_auth_hdr *ah = (struct ip_auth_hdr *)(skb->data+(iph->ihl<<2));
 	struct xfrm_state *x;
 
@@ -404,7 +404,8 @@ static void ah4_err(struct sk_buff *skb, u32 info)
 	    icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 		return;
 
-	x = xfrm_state_lookup(net, skb->mark, (xfrm_address_t *)&iph->daddr, ah->spi, IPPROTO_AH, AF_INET);
+	x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
+			      ah->spi, IPPROTO_AH, AF_INET);
 	if (!x)
 		return;
 	printk(KERN_DEBUG "pmtu discovery on SA AH/%08x/%08x\n",
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 03f994bcf7de..a5b413416da3 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -276,7 +276,7 @@ error:
 
 static int esp_input_done2(struct sk_buff *skb, int err)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	struct xfrm_state *x = xfrm_input_state(skb);
 	struct esp_data *esp = x->data;
 	struct crypto_aead *aead = esp->aead;
@@ -484,7 +484,7 @@ static u32 esp4_get_mtu(struct xfrm_state *x, int mtu)
 static void esp4_err(struct sk_buff *skb, u32 info)
 {
 	struct net *net = dev_net(skb->dev);
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	struct ip_esp_hdr *esph = (struct ip_esp_hdr *)(skb->data+(iph->ihl<<2));
 	struct xfrm_state *x;
 
@@ -492,7 +492,8 @@ static void esp4_err(struct sk_buff *skb, u32 info)
 	    icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
 		return;
 
-	x = xfrm_state_lookup(net, skb->mark, (xfrm_address_t *)&iph->daddr, esph->spi, IPPROTO_ESP, AF_INET);
+	x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
+			      esph->spi, IPPROTO_ESP, AF_INET);
 	if (!x)
 		return;
 	NETDEBUG(KERN_DEBUG "pmtu discovery on SA ESP/%08x/%08x\n",
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index e5f8a71d3a2a..74e35e5736e2 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -373,7 +373,7 @@ out_unlock:
 }
 
 static struct rtable *icmp_route_lookup(struct net *net, struct sk_buff *skb_in,
-					struct iphdr *iph,
+					const struct iphdr *iph,
 					__be32 saddr, u8 tos,
 					int type, int code,
 					struct icmp_bxm *param)
@@ -637,7 +637,7 @@ EXPORT_SYMBOL(icmp_send);
 
 static void icmp_unreach(struct sk_buff *skb)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	struct icmphdr *icmph;
 	int hash, protocol;
 	const struct net_protocol *ipprot;
@@ -656,7 +656,7 @@ static void icmp_unreach(struct sk_buff *skb)
 		goto out_err;
 
 	icmph = icmp_hdr(skb);
-	iph   = (struct iphdr *)skb->data;
+	iph   = (const struct iphdr *)skb->data;
 
 	if (iph->ihl < 5) /* Mangled header, drop. */
 		goto out_err;
@@ -729,7 +729,7 @@ static void icmp_unreach(struct sk_buff *skb)
 	if (!pskb_may_pull(skb, iph->ihl * 4 + 8))
 		goto out;
 
-	iph = (struct iphdr *)skb->data;
+	iph = (const struct iphdr *)skb->data;
 	protocol = iph->protocol;
 
 	/*
@@ -758,7 +758,7 @@ out_err:
 
 static void icmp_redirect(struct sk_buff *skb)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 
 	if (skb->len < sizeof(struct iphdr))
 		goto out_err;
@@ -769,7 +769,7 @@ static void icmp_redirect(struct sk_buff *skb)
 	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
 		goto out;
 
-	iph = (struct iphdr *)skb->data;
+	iph = (const struct iphdr *)skb->data;
 
 	switch (icmp_hdr(skb)->code & 7) {
 	case ICMP_REDIR_NET:
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 2ada17129fce..6ffe94ca5bc9 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -124,7 +124,7 @@ static int inet_csk_diag_fill(struct sock *sk,
 
 #if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
 	if (r->idiag_family == AF_INET6) {
-		struct ipv6_pinfo *np = inet6_sk(sk);
+		const struct ipv6_pinfo *np = inet6_sk(sk);
 
 		ipv6_addr_copy((struct in6_addr *)r->id.idiag_src,
 			       &np->rcv_saddr);
diff --git a/net/ipv4/inet_lro.c b/net/ipv4/inet_lro.c
index 47038cb6c138..85a0f75dae64 100644
--- a/net/ipv4/inet_lro.c
+++ b/net/ipv4/inet_lro.c
@@ -51,8 +51,8 @@ MODULE_DESCRIPTION("Large Receive Offload (ipv4 / tcp)");
  * Basic tcp checks whether packet is suitable for LRO
  */
 
-static int lro_tcp_ip_check(struct iphdr *iph, struct tcphdr *tcph,
-			    int len, struct net_lro_desc *lro_desc)
+static int lro_tcp_ip_check(const struct iphdr *iph, const struct tcphdr *tcph,
+			    int len, const struct net_lro_desc *lro_desc)
 {
         /* check ip header: don't aggregate padded frames */
 	if (ntohs(iph->tot_len) != len)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index da5941f18c3c..24efd353279a 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -462,7 +462,7 @@ static void ipgre_err(struct sk_buff *skb, u32 info)
    by themself???
  */
 
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	__be16	     *p = (__be16*)(skb->data+(iph->ihl<<2));
 	int grehlen = (iph->ihl<<2) + 4;
 	const int type = icmp_hdr(skb)->type;
@@ -534,7 +534,7 @@ out:
 	rcu_read_unlock();
 }
 
-static inline void ipgre_ecn_decapsulate(struct iphdr *iph, struct sk_buff *skb)
+static inline void ipgre_ecn_decapsulate(const struct iphdr *iph, struct sk_buff *skb)
 {
 	if (INET_ECN_is_ce(iph->tos)) {
 		if (skb->protocol == htons(ETH_P_IP)) {
@@ -546,19 +546,19 @@ static inline void ipgre_ecn_decapsulate(struct iphdr *iph, struct sk_buff *skb)
 }
 
 static inline u8
-ipgre_ecn_encapsulate(u8 tos, struct iphdr *old_iph, struct sk_buff *skb)
+ipgre_ecn_encapsulate(u8 tos, const struct iphdr *old_iph, struct sk_buff *skb)
 {
 	u8 inner = 0;
 	if (skb->protocol == htons(ETH_P_IP))
 		inner = old_iph->tos;
 	else if (skb->protocol == htons(ETH_P_IPV6))
-		inner = ipv6_get_dsfield((struct ipv6hdr *)old_iph);
+		inner = ipv6_get_dsfield((const struct ipv6hdr *)old_iph);
 	return INET_ECN_encapsulate(tos, inner);
 }
 
 static int ipgre_rcv(struct sk_buff *skb)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	u8     *h;
 	__be16    flags;
 	__sum16   csum = 0;
@@ -697,8 +697,8 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct pcpu_tstats *tstats;
-	struct iphdr  *old_iph = ip_hdr(skb);
-	struct iphdr  *tiph;
+	const struct iphdr  *old_iph = ip_hdr(skb);
+	const struct iphdr  *tiph;
 	u8     tos;
 	__be16 df;
 	struct rtable *rt;     			/* Route to the other host */
@@ -714,7 +714,7 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 
 	if (dev->header_ops && dev->type == ARPHRD_IPGRE) {
 		gre_hlen = 0;
-		tiph = (struct iphdr *)skb->data;
+		tiph = (const struct iphdr *)skb->data;
 	} else {
 		gre_hlen = tunnel->hlen;
 		tiph = &tunnel->parms.iph;
@@ -735,14 +735,14 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 		}
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 		else if (skb->protocol == htons(ETH_P_IPV6)) {
-			struct in6_addr *addr6;
+			const struct in6_addr *addr6;
 			int addr_type;
 			struct neighbour *neigh = skb_dst(skb)->neighbour;
 
 			if (neigh == NULL)
 				goto tx_error;
 
-			addr6 = (struct in6_addr *)&neigh->primary_key;
+			addr6 = (const struct in6_addr *)&neigh->primary_key;
 			addr_type = ipv6_addr_type(addr6);
 
 			if (addr_type == IPV6_ADDR_ANY) {
@@ -766,7 +766,7 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 		if (skb->protocol == htons(ETH_P_IP))
 			tos = old_iph->tos;
 		else if (skb->protocol == htons(ETH_P_IPV6))
-			tos = ipv6_get_dsfield((struct ipv6hdr *)old_iph);
+			tos = ipv6_get_dsfield((const struct ipv6hdr *)old_iph);
 	}
 
 	rt = ip_route_output_gre(dev_net(dev), dst, tiph->saddr,
@@ -881,7 +881,7 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
 			iph->ttl = old_iph->ttl;
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 		else if (skb->protocol == htons(ETH_P_IPV6))
-			iph->ttl = ((struct ipv6hdr *)old_iph)->hop_limit;
+			iph->ttl = ((const struct ipv6hdr *)old_iph)->hop_limit;
 #endif
 		else
 			iph->ttl = ip4_dst_hoplimit(&rt->dst);
@@ -927,7 +927,7 @@ static int ipgre_tunnel_bind_dev(struct net_device *dev)
 {
 	struct net_device *tdev = NULL;
 	struct ip_tunnel *tunnel;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	int hlen = LL_MAX_HEADER;
 	int mtu = ETH_DATA_LEN;
 	int addend = sizeof(struct iphdr) + 4;
@@ -1180,7 +1180,7 @@ static int ipgre_header(struct sk_buff *skb, struct net_device *dev,
 
 static int ipgre_header_parse(const struct sk_buff *skb, unsigned char *haddr)
 {
-	struct iphdr *iph = (struct iphdr *) skb_mac_header(skb);
+	const struct iphdr *iph = (const struct iphdr *) skb_mac_header(skb);
 	memcpy(haddr, &iph->saddr, 4);
 	return 4;
 }
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index d7b2b0987a3b..c8f48efc5fd3 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -268,7 +268,7 @@ int ip_local_deliver(struct sk_buff *skb)
 static inline int ip_rcv_options(struct sk_buff *skb)
 {
 	struct ip_options *opt;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	struct net_device *dev = skb->dev;
 
 	/* It looks as overkill, because not all
@@ -374,7 +374,7 @@ drop:
  */
 int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt, struct net_device *orig_dev)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	u32 len;
 
 	/* When the interface is in promisc. mode, drop all the crap
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 3948c86e59ca..9640900309bb 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -131,7 +131,7 @@ static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
 static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
 {
 	struct sockaddr_in sin;
-	struct iphdr *iph = ip_hdr(skb);
+	const struct iphdr *iph = ip_hdr(skb);
 	__be16 *ports = (__be16 *)skb_transport_header(skb);
 
 	if (skb_transport_offset(skb) + 4 > skb->len)
diff --git a/net/ipv4/ipcomp.c b/net/ipv4/ipcomp.c
index 629067571f02..c857f6f49b03 100644
--- a/net/ipv4/ipcomp.c
+++ b/net/ipv4/ipcomp.c
@@ -27,7 +27,7 @@ static void ipcomp4_err(struct sk_buff *skb, u32 info)
 {
 	struct net *net = dev_net(skb->dev);
 	__be32 spi;
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	struct ip_comp_hdr *ipch = (struct ip_comp_hdr *)(skb->data+(iph->ihl<<2));
 	struct xfrm_state *x;
 
@@ -36,7 +36,7 @@ static void ipcomp4_err(struct sk_buff *skb, u32 info)
 		return;
 
 	spi = htonl(ntohs(ipch->cpi));
-	x = xfrm_state_lookup(net, skb->mark, (xfrm_address_t *)&iph->daddr,
+	x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
 			      spi, IPPROTO_COMP, AF_INET);
 	if (!x)
 		return;
diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index bfc17c5914e7..ef16377ec73f 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -319,7 +319,7 @@ static int ipip_err(struct sk_buff *skb, u32 info)
    8 bytes of packet payload. It means, that precise relaying of
    ICMP in the real Internet is absolutely infeasible.
  */
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	const int type = icmp_hdr(skb)->type;
 	const int code = icmp_hdr(skb)->code;
 	struct ip_tunnel *t;
@@ -433,12 +433,12 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ip_tunnel *tunnel = netdev_priv(dev);
 	struct pcpu_tstats *tstats;
-	struct iphdr  *tiph = &tunnel->parms.iph;
+	const struct iphdr  *tiph = &tunnel->parms.iph;
 	u8     tos = tunnel->parms.iph.tos;
 	__be16 df = tiph->frag_off;
 	struct rtable *rt;     			/* Route to the other host */
 	struct net_device *tdev;		/* Device to other host */
-	struct iphdr  *old_iph = ip_hdr(skb);
+	const struct iphdr  *old_iph = ip_hdr(skb);
 	struct iphdr  *iph;			/* Our new IP header */
 	unsigned int max_headroom;		/* The extra header space needed */
 	__be32 dst = tiph->daddr;
@@ -572,7 +572,7 @@ static void ipip_tunnel_bind_dev(struct net_device *dev)
 {
 	struct net_device *tdev = NULL;
 	struct ip_tunnel *tunnel;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 
 	tunnel = netdev_priv(dev);
 	iph = &tunnel->parms.iph;
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 1f62eaeb6de4..c81b9b661d26 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1549,7 +1549,7 @@ static struct notifier_block ip_mr_notifier = {
 static void ip_encap(struct sk_buff *skb, __be32 saddr, __be32 daddr)
 {
 	struct iphdr *iph;
-	struct iphdr *old_iph = ip_hdr(skb);
+	const struct iphdr *old_iph = ip_hdr(skb);
 
 	skb_push(skb, sizeof(struct iphdr));
 	skb->transport_header = skb->network_header;
diff --git a/net/ipv4/netfilter/nf_nat_helper.c b/net/ipv4/netfilter/nf_nat_helper.c
index 31427fb57aa8..99cfa28b6d38 100644
--- a/net/ipv4/netfilter/nf_nat_helper.c
+++ b/net/ipv4/netfilter/nf_nat_helper.c
@@ -153,7 +153,7 @@ void nf_nat_set_seq_adjust(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 }
 EXPORT_SYMBOL_GPL(nf_nat_set_seq_adjust);
 
-static void nf_nat_csum(struct sk_buff *skb, struct iphdr *iph, void *data,
+static void nf_nat_csum(struct sk_buff *skb, const struct iphdr *iph, void *data,
 			int datalen, __sum16 *check, int oldlen)
 {
 	struct rtable *rt = skb_rtable(skb);
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index 2b50cc2da90a..abf14dbcb3b9 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -154,7 +154,7 @@ static __inline__ int icmp_filter(struct sock *sk, struct sk_buff *skb)
  * RFC 1122: SHOULD pass TOS value up to the transport layer.
  * -> It does. And not only TOS, but all IP header.
  */
-static int raw_v4_input(struct sk_buff *skb, struct iphdr *iph, int hash)
+static int raw_v4_input(struct sk_buff *skb, const struct iphdr *iph, int hash)
 {
 	struct sock *sk;
 	struct hlist_head *head;
@@ -247,7 +247,7 @@ static void raw_err(struct sock *sk, struct sk_buff *skb, u32 info)
 	}
 
 	if (inet->recverr) {
-		struct iphdr *iph = (struct iphdr *)skb->data;
+		const struct iphdr *iph = (const struct iphdr *)skb->data;
 		u8 *payload = skb->data + (iph->ihl << 2);
 
 		if (inet->hdrincl)
@@ -265,7 +265,7 @@ void raw_icmp_error(struct sk_buff *skb, int protocol, u32 info)
 {
 	int hash;
 	struct sock *raw_sk;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	struct net *net;
 
 	hash = protocol & (RAW_HTABLE_SIZE - 1);
@@ -273,7 +273,7 @@ void raw_icmp_error(struct sk_buff *skb, int protocol, u32 info)
 	read_lock(&raw_v4_hashinfo.lock);
 	raw_sk = sk_head(&raw_v4_hashinfo.ht[hash]);
 	if (raw_sk != NULL) {
-		iph = (struct iphdr *)skb->data;
+		iph = (const struct iphdr *)skb->data;
 		net = dev_net(skb->dev);
 
 		while ((raw_sk = __raw_v4_lookup(net, raw_sk, protocol,
@@ -281,7 +281,7 @@ void raw_icmp_error(struct sk_buff *skb, int protocol, u32 info)
 						skb->dev->ifindex)) != NULL) {
 			raw_err(raw_sk, skb, info);
 			raw_sk = sk_next(raw_sk);
-			iph = (struct iphdr *)skb->data;
+			iph = (const struct iphdr *)skb->data;
 		}
 	}
 	read_unlock(&raw_v4_hashinfo.lock);
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e9aee81de3e3..f4b7f806afd8 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1507,7 +1507,7 @@ static inline unsigned short guess_mtu(unsigned short old_mtu)
 	return 68;
 }
 
-unsigned short ip_rt_frag_needed(struct net *net, struct iphdr *iph,
+unsigned short ip_rt_frag_needed(struct net *net, const struct iphdr *iph,
 				 unsigned short new_mtu,
 				 struct net_device *dev)
 {
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index f7e6c2c2d2bb..edf18bd74b87 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -279,7 +279,7 @@ EXPORT_SYMBOL(tcp_v4_connect);
 /*
  * This routine does path mtu discovery as defined in RFC1191.
  */
-static void do_pmtu_discovery(struct sock *sk, struct iphdr *iph, u32 mtu)
+static void do_pmtu_discovery(struct sock *sk, const struct iphdr *iph, u32 mtu)
 {
 	struct dst_entry *dst;
 	struct inet_sock *inet = inet_sk(sk);
@@ -341,7 +341,7 @@ static void do_pmtu_discovery(struct sock *sk, struct iphdr *iph, u32 mtu)
 
 void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 {
-	struct iphdr *iph = (struct iphdr *)icmp_skb->data;
+	const struct iphdr *iph = (const struct iphdr *)icmp_skb->data;
 	struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2));
 	struct inet_connection_sock *icsk;
 	struct tcp_sock *tp;
@@ -2527,7 +2527,7 @@ void tcp4_proc_exit(void)
 
 struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 {
-	struct iphdr *iph = skb_gro_network_header(skb);
+	const struct iphdr *iph = skb_gro_network_header(skb);
 
 	switch (skb->ip_summed) {
 	case CHECKSUM_COMPLETE:
@@ -2548,7 +2548,7 @@ struct sk_buff **tcp4_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 
 int tcp4_gro_complete(struct sk_buff *skb)
 {
-	struct iphdr *iph = ip_hdr(skb);
+	const struct iphdr *iph = ip_hdr(skb);
 	struct tcphdr *th = tcp_hdr(skb);
 
 	th->check = ~tcp_v4_check(skb->len - skb_transport_offset(skb),
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index a15c8fb653af..bc0dab2593e0 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -578,7 +578,7 @@ found:
 void __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
 {
 	struct inet_sock *inet;
-	struct iphdr *iph = (struct iphdr *)skb->data;
+	const struct iphdr *iph = (const struct iphdr *)skb->data;
 	struct udphdr *uh = (struct udphdr *)(skb->data+(iph->ihl<<2));
 	const int type = icmp_hdr(skb)->type;
 	const int code = icmp_hdr(skb)->code;
diff --git a/net/ipv4/xfrm4_policy.c b/net/ipv4/xfrm4_policy.c
index d20a05e970d8..59b1340fb3bf 100644
--- a/net/ipv4/xfrm4_policy.c
+++ b/net/ipv4/xfrm4_policy.c
@@ -102,7 +102,7 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 static void
 _decode_session4(struct sk_buff *skb, struct flowi *fl, int reverse)
 {
-	struct iphdr *iph = ip_hdr(skb);
+	const struct iphdr *iph = ip_hdr(skb);
 	u8 *xprth = skb_network_header(skb) + iph->ihl * 4;
 	struct flowi4 *fl4 = &fl->u.ip4;
 
diff --git a/net/ipv4/xfrm4_state.c b/net/ipv4/xfrm4_state.c
index 1717c64628d1..ea983ae96ae6 100644
--- a/net/ipv4/xfrm4_state.c
+++ b/net/ipv4/xfrm4_state.c
@@ -55,7 +55,7 @@ xfrm4_init_temprop(struct xfrm_state *x, const struct xfrm_tmpl *tmpl,
 
 int xfrm4_extract_header(struct sk_buff *skb)
 {
-	struct iphdr *iph = ip_hdr(skb);
+	const struct iphdr *iph = ip_hdr(skb);
 
 	XFRM_MODE_SKB_CB(skb)->ihl = sizeof(*iph);
 	XFRM_MODE_SKB_CB(skb)->id = iph->id;