tcp: add const qualifiers where possible

Adding const qualifiers to pointers can ease code review, and spot some
bugs. It might allow compiler to optimize code further.

For example, is it legal to temporary write a null cksum into tcphdr
in tcp_md5_hash_header() ? I am afraid a sniffer could catch the
temporary null value...

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

2 files changed, 17 insertions, 16 deletions

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index ac838965ff34..5a0d6648bbbc 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -115,7 +115,7 @@ static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
 		& COOKIEMASK;
 }
 
-__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
+__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct tcphdr *th = tcp_hdr(skb);
@@ -137,7 +137,7 @@ __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
 				     jiffies / (HZ * 60), mssind);
 }
 
-static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
+static inline int cookie_check(const struct sk_buff *skb, __u32 cookie)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct tcphdr *th = tcp_hdr(skb);
@@ -152,7 +152,7 @@ static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 {
 	struct tcp_options_received tcp_opt;
-	u8 *hash_location;
+	const u8 *hash_location;
 	struct inet_request_sock *ireq;
 	struct inet6_request_sock *ireq6;
 	struct tcp_request_sock *treq;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 5357902c7978..da2ada881cfa 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -114,7 +114,7 @@ static __inline__ __sum16 tcp_v6_check(int len,
 	return csum_ipv6_magic(saddr, daddr, len, IPPROTO_TCP, base);
 }
 
-static __u32 tcp_v6_init_sequence(struct sk_buff *skb)
+static __u32 tcp_v6_init_sequence(const struct sk_buff *skb)
 {
 	return secure_tcpv6_sequence_number(ipv6_hdr(skb)->daddr.s6_addr32,
 					    ipv6_hdr(skb)->saddr.s6_addr32,
@@ -844,7 +844,7 @@ clear_hash_noput:
 
 static int tcp_v6_inbound_md5_hash (struct sock *sk, struct sk_buff *skb)
 {
-	__u8 *hash_location = NULL;
+	const __u8 *hash_location = NULL;
 	struct tcp_md5sig_key *hash_expected;
 	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 	struct tcphdr *th = tcp_hdr(skb);
@@ -980,7 +980,8 @@ static int tcp6_gro_complete(struct sk_buff *skb)
 static void tcp_v6_send_response(struct sk_buff *skb, u32 seq, u32 ack, u32 win,
 				 u32 ts, struct tcp_md5sig_key *key, int rst)
 {
-	struct tcphdr *th = tcp_hdr(skb), *t1;
+	const struct tcphdr *th = tcp_hdr(skb);
+	struct tcphdr *t1;
 	struct sk_buff *buff;
 	struct flowi6 fl6;
 	struct net *net = dev_net(skb_dst(skb)->dev);
@@ -1070,7 +1071,7 @@ static void tcp_v6_send_response(struct sk_buff *skb, u32 seq, u32 ack, u32 win,
 
 static void tcp_v6_send_reset(struct sock *sk, struct sk_buff *skb)
 {
-	struct tcphdr *th = tcp_hdr(skb);
+	const struct tcphdr *th = tcp_hdr(skb);
 	u32 seq = 0, ack_seq = 0;
 	struct tcp_md5sig_key *key = NULL;
 
@@ -1160,7 +1161,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 {
 	struct tcp_extend_values tmp_ext;
 	struct tcp_options_received tmp_opt;
-	u8 *hash_location;
+	const u8 *hash_location;
 	struct request_sock *req;
 	struct inet6_request_sock *treq;
 	struct ipv6_pinfo *np = inet6_sk(sk);
@@ -1688,7 +1689,7 @@ ipv6_pktoptions:
 
 static int tcp_v6_rcv(struct sk_buff *skb)
 {
-	struct tcphdr *th;
+	const struct tcphdr *th;
 	const struct ipv6hdr *hdr;
 	struct sock *sk;
 	int ret;
@@ -1856,8 +1857,8 @@ static struct inet_peer *tcp_v6_get_peer(struct sock *sk, bool *release_it)
 
 static void *tcp_v6_tw_get_peer(struct sock *sk)
 {
-	struct inet6_timewait_sock *tw6 = inet6_twsk(sk);
-	struct inet_timewait_sock *tw = inet_twsk(sk);
+	const struct inet6_timewait_sock *tw6 = inet6_twsk(sk);
+	const struct inet_timewait_sock *tw = inet_twsk(sk);
 
 	if (tw->tw_family == AF_INET)
 		return tcp_v4_tw_get_peer(sk);
@@ -2012,7 +2013,7 @@ static void tcp_v6_destroy_sock(struct sock *sk)
 #ifdef CONFIG_PROC_FS
 /* Proc filesystem TCPv6 sock list dumping. */
 static void get_openreq6(struct seq_file *seq,
-			 struct sock *sk, struct request_sock *req, int i, int uid)
+			 const struct sock *sk, struct request_sock *req, int i, int uid)
 {
 	int ttd = req->expires - jiffies;
 	const struct in6_addr *src = &inet6_rsk(req)->loc_addr;
@@ -2048,10 +2049,10 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
 	__u16 destp, srcp;
 	int timer_active;
 	unsigned long timer_expires;
-	struct inet_sock *inet = inet_sk(sp);
-	struct tcp_sock *tp = tcp_sk(sp);
+	const struct inet_sock *inet = inet_sk(sp);
+	const struct tcp_sock *tp = tcp_sk(sp);
 	const struct inet_connection_sock *icsk = inet_csk(sp);
-	struct ipv6_pinfo *np = inet6_sk(sp);
+	const struct ipv6_pinfo *np = inet6_sk(sp);
 
 	dest  = &np->daddr;
 	src   = &np->rcv_saddr;
@@ -2103,7 +2104,7 @@ static void get_timewait6_sock(struct seq_file *seq,
 {
 	const struct in6_addr *dest, *src;
 	__u16 destp, srcp;
-	struct inet6_timewait_sock *tw6 = inet6_twsk((struct sock *)tw);
+	const struct inet6_timewait_sock *tw6 = inet6_twsk((struct sock *)tw);
 	int ttd = tw->tw_ttd - jiffies;
 
 	if (ttd < 0)