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, 24 insertions, 21 deletions

diff --git a/include/net/secure_seq.h b/include/net/secure_seq.h
index d97f689..c2e542b 100644
--- a/include/net/secure_seq.h
+++ b/include/net/secure_seq.h
@@ -10,7 +10,7 @@ extern u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
 				      __be16 dport);
 extern __u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
 					__be16 sport, __be16 dport);
-extern __u32 secure_tcpv6_sequence_number(__be32 *saddr, __be32 *daddr,
+extern __u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
 					  __be16 sport, __be16 dport);
 extern u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
 				       __be16 sport, __be16 dport);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0113d30..3edef0b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -327,9 +327,9 @@ extern int tcp_sendpage(struct sock *sk, struct page *page, int offset,
 			size_t size, int flags);
 extern int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
 extern int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
-				 struct tcphdr *th, unsigned len);
+				 const struct tcphdr *th, unsigned int len);
 extern int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
-			       struct tcphdr *th, unsigned len);
+			       const struct tcphdr *th, unsigned int len);
 extern void tcp_rcv_space_adjust(struct sock *sk);
 extern void tcp_cleanup_rbuf(struct sock *sk, int copied);
 extern int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
@@ -401,10 +401,10 @@ extern void tcp_set_keepalive(struct sock *sk, int val);
 extern void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req);
 extern int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		       size_t len, int nonblock, int flags, int *addr_len);
-extern void tcp_parse_options(struct sk_buff *skb,
-			      struct tcp_options_received *opt_rx, u8 **hvpp,
+extern void tcp_parse_options(const struct sk_buff *skb,
+			      struct tcp_options_received *opt_rx, const u8 **hvpp,
 			      int estab);
-extern u8 *tcp_parse_md5sig_option(struct tcphdr *th);
+extern const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
 
 /*
  *	TCP v4 functions exported for the inet6 API
@@ -450,7 +450,7 @@ extern bool cookie_check_timestamp(struct tcp_options_received *opt, bool *);
 /* From net/ipv6/syncookies.c */
 extern struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
 #ifdef CONFIG_SYN_COOKIES
-extern __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb,
+extern __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb,
 				     __u16 *mss);
 #else
 static inline __u32 cookie_v6_init_sequence(struct sock *sk,
@@ -522,7 +522,7 @@ static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
 }
 
 /* tcp.c */
-extern void tcp_get_info(struct sock *, struct tcp_info *);
+extern void tcp_get_info(const struct sock *, struct tcp_info *);
 
 /* Read 'sendfile()'-style from a TCP socket */
 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
@@ -532,8 +532,8 @@ extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 
 extern void tcp_initialize_rcv_mss(struct sock *sk);
 
-extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);
-extern int tcp_mss_to_mtu(struct sock *sk, int mss);
+extern int tcp_mtu_to_mss(const struct sock *sk, int pmtu);
+extern int tcp_mss_to_mtu(const struct sock *sk, int mss);
 extern void tcp_mtup_init(struct sock *sk);
 extern void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt);
 
@@ -574,7 +574,7 @@ static inline void tcp_fast_path_check(struct sock *sk)
 /* Compute the actual rto_min value */
 static inline u32 tcp_rto_min(struct sock *sk)
 {
-	struct dst_entry *dst = __sk_dst_get(sk);
+	const struct dst_entry *dst = __sk_dst_get(sk);
 	u32 rto_min = TCP_RTO_MIN;
 
 	if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
@@ -820,6 +820,7 @@ static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
+
 	if ((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_CWR | TCPF_CA_Recovery))
 		return tp->snd_ssthresh;
 	else
@@ -832,7 +833,7 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 #define tcp_verify_left_out(tp)	WARN_ON(tcp_left_out(tp) > tp->packets_out)
 
 extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
-extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
+extern __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
 
 /* Slow start with delack produces 3 packets of burst, so that
  * it is safe "de facto".  This will be the default - same as
@@ -861,7 +862,7 @@ static inline void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss,
 
 static inline void tcp_check_probe_timer(struct sock *sk)
 {
-	struct tcp_sock *tp = tcp_sk(sk);
+	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	if (!tp->packets_out && !icsk->icsk_pending)
@@ -1209,10 +1210,10 @@ extern struct tcp_md5sig_pool	*tcp_get_md5sig_pool(void);
 extern void tcp_put_md5sig_pool(void);
 
 extern int tcp_md5_hash_header(struct tcp_md5sig_pool *, struct tcphdr *);
-extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, struct sk_buff *,
+extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
 				 unsigned header_len);
 extern int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
-			    struct tcp_md5sig_key *key);
+			    const struct tcp_md5sig_key *key);
 
 /* write queue abstraction */
 static inline void tcp_write_queue_purge(struct sock *sk)
@@ -1225,22 +1226,24 @@ static inline void tcp_write_queue_purge(struct sock *sk)
 	tcp_clear_all_retrans_hints(tcp_sk(sk));
 }
 
-static inline struct sk_buff *tcp_write_queue_head(struct sock *sk)
+static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
 {
 	return skb_peek(&sk->sk_write_queue);
 }
 
-static inline struct sk_buff *tcp_write_queue_tail(struct sock *sk)
+static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
 {
 	return skb_peek_tail(&sk->sk_write_queue);
 }
 
-static inline struct sk_buff *tcp_write_queue_next(struct sock *sk, struct sk_buff *skb)
+static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
+						   const struct sk_buff *skb)
 {
 	return skb_queue_next(&sk->sk_write_queue, skb);
 }
 
-static inline struct sk_buff *tcp_write_queue_prev(struct sock *sk, struct sk_buff *skb)
+static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
+						   const struct sk_buff *skb)
 {
 	return skb_queue_prev(&sk->sk_write_queue, skb);
 }
@@ -1254,7 +1257,7 @@ static inline struct sk_buff *tcp_write_queue_prev(struct sock *sk, struct sk_bu
 #define tcp_for_write_queue_from_safe(skb, tmp, sk)			\
 	skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
 
-static inline struct sk_buff *tcp_send_head(struct sock *sk)
+static inline struct sk_buff *tcp_send_head(const struct sock *sk)
 {
 	return sk->sk_send_head;
 }
@@ -1265,7 +1268,7 @@ static inline bool tcp_skb_is_last(const struct sock *sk,
 	return skb_queue_is_last(&sk->sk_write_queue, skb);
 }
 
-static inline void tcp_advance_send_head(struct sock *sk, struct sk_buff *skb)
+static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
 {
 	if (tcp_skb_is_last(sk, skb))
 		sk->sk_send_head = NULL;