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>

1 files changed, 56 insertions, 54 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 69a90b839984..52b5c2d0ecd0 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -206,7 +206,7 @@ static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 }
 
-static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
+static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
 {
         if (tcp_hdr(skb)->cwr)
                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
@@ -239,19 +239,19 @@ static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *s
         }
 }
 
-static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
+static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 {
         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
                 tp->ecn_flags &= ~TCP_ECN_OK;
 }
 
-static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
+static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 {
         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
                 tp->ecn_flags &= ~TCP_ECN_OK;
 }
 
-static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
+static inline int TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 {
         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
                 return 1;
@@ -315,7 +315,7 @@ static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
         return 0;
 }
 
-static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
+static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
@@ -429,7 +429,7 @@ static void tcp_clamp_window(struct sock *sk)
  */
 void tcp_initialize_rcv_mss(struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 
         hint = min(hint, tp->rcv_wnd / 2);
@@ -824,7 +824,7 @@ void tcp_update_metrics(struct sock *sk)
         }
 }
 
-__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
+__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 {
         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 
@@ -1216,7 +1216,7 @@ static void tcp_mark_lost_retrans(struct sock *sk)
                 tp->lost_retrans_low = new_low_seq;
 }
 
-static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
+static int tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
                            struct tcp_sack_block_wire *sp, int num_sacks,
                            u32 prior_snd_una)
 {
@@ -1310,7 +1310,7 @@ static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
         return in_sack;
 }
 
-static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
+static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
                           struct tcp_sacktag_state *state,
                           int dup_sack, int pcount)
 {
@@ -1465,13 +1465,13 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
 /* I wish gso_size would have a bit more sane initialization than
  * something-or-zero which complicates things
  */
-static int tcp_skb_seglen(struct sk_buff *skb)
+static int tcp_skb_seglen(const struct sk_buff *skb)
 {
         return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
 }
 
 /* Shifting pages past head area doesn't work */
-static int skb_can_shift(struct sk_buff *skb)
+static int skb_can_shift(const struct sk_buff *skb)
 {
         return !skb_headlen(skb) && skb_is_nonlinear(skb);
 }
@@ -1720,19 +1720,19 @@ static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
         return skb;
 }
 
-static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
+static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
 {
         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
 }
 
 static int
-tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
+tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
                         u32 prior_snd_una)
 {
         const struct inet_connection_sock *icsk = inet_csk(sk);
         struct tcp_sock *tp = tcp_sk(sk);
-        unsigned char *ptr = (skb_transport_header(ack_skb) +
-                              TCP_SKB_CB(ack_skb)->sacked);
+        const unsigned char *ptr = (skb_transport_header(ack_skb) +
+                                    TCP_SKB_CB(ack_skb)->sacked);
         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
         struct tcp_sack_block sp[TCP_NUM_SACKS];
         struct tcp_sack_block *cache;
@@ -2296,7 +2296,7 @@ static int tcp_check_sack_reneging(struct sock *sk, int flag)
         return 0;
 }
 
-static inline int tcp_fackets_out(struct tcp_sock *tp)
+static inline int tcp_fackets_out(const struct tcp_sock *tp)
 {
         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
 }
@@ -2316,19 +2316,20 @@ static inline int tcp_fackets_out(struct tcp_sock *tp)
  * they differ. Since neither occurs due to loss, TCP should really
  * ignore them.
  */
-static inline int tcp_dupack_heuristics(struct tcp_sock *tp)
+static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
 {
         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
 }
 
-static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
+static inline int tcp_skb_timedout(const struct sock *sk,
+                                   const struct sk_buff *skb)
 {
         return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
 }
 
-static inline int tcp_head_timedout(struct sock *sk)
+static inline int tcp_head_timedout(const struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
 
         return tp->packets_out &&
                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
@@ -2639,7 +2640,7 @@ static void tcp_cwnd_down(struct sock *sk, int flag)
 /* Nothing was retransmitted or returned timestamp is less
  * than timestamp of the first retransmission.
  */
-static inline int tcp_packet_delayed(struct tcp_sock *tp)
+static inline int tcp_packet_delayed(const struct tcp_sock *tp)
 {
         return !tp->retrans_stamp ||
                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
@@ -2700,7 +2701,7 @@ static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
         tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
-static inline int tcp_may_undo(struct tcp_sock *tp)
+static inline int tcp_may_undo(const struct tcp_sock *tp)
 {
         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
 }
@@ -2764,9 +2765,9 @@ static void tcp_try_undo_dsack(struct sock *sk)
  * that successive retransmissions of a segment must not advance
  * retrans_stamp under any conditions.
  */
-static int tcp_any_retrans_done(struct sock *sk)
+static int tcp_any_retrans_done(const struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
 
         if (tp->retrans_out)
@@ -3245,7 +3246,7 @@ static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
  */
 static void tcp_rearm_rto(struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
 
         if (!tp->packets_out) {
                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
@@ -3497,7 +3498,7 @@ static inline int tcp_may_update_window(const struct tcp_sock *tp,
  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
  */
-static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
+static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
                                  u32 ack_seq)
 {
         struct tcp_sock *tp = tcp_sk(sk);
@@ -3673,7 +3674,7 @@ static int tcp_process_frto(struct sock *sk, int flag)
 }
 
 /* This routine deals with incoming acks, but not outgoing ones. */
-static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
+static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 {
         struct inet_connection_sock *icsk = inet_csk(sk);
         struct tcp_sock *tp = tcp_sk(sk);
@@ -3810,14 +3811,14 @@ old_ack:
  * But, this can also be called on packets in the established flow when
  * the fast version below fails.
  */
-void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
-                       u8 **hvpp, int estab)
+void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
+                       const u8 **hvpp, int estab)
 {
-        unsigned char *ptr;
-        struct tcphdr *th = tcp_hdr(skb);
+        const unsigned char *ptr;
+        const struct tcphdr *th = tcp_hdr(skb);
         int length = (th->doff * 4) - sizeof(struct tcphdr);
 
-        ptr = (unsigned char *)(th + 1);
+        ptr = (const unsigned char *)(th + 1);
         opt_rx->saw_tstamp = 0;
 
         while (length > 0) {
@@ -3928,9 +3929,9 @@ void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
 }
 EXPORT_SYMBOL(tcp_parse_options);
 
-static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
+static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
 {
-        __be32 *ptr = (__be32 *)(th + 1);
+        const __be32 *ptr = (const __be32 *)(th + 1);
 
         if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
@@ -3947,8 +3948,9 @@ static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
 /* Fast parse options. This hopes to only see timestamps.
  * If it is wrong it falls back on tcp_parse_options().
  */
-static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
-                                  struct tcp_sock *tp, u8 **hvpp)
+static int tcp_fast_parse_options(const struct sk_buff *skb,
+                                  const struct tcphdr *th,
+                                  struct tcp_sock *tp, const u8 **hvpp)
 {
         /* In the spirit of fast parsing, compare doff directly to constant
          * values.  Because equality is used, short doff can be ignored here.
@@ -3969,10 +3971,10 @@ static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
 /*
  * Parse MD5 Signature option
  */
-u8 *tcp_parse_md5sig_option(struct tcphdr *th)
+const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
 {
-        int length = (th->doff << 2) - sizeof (*th);
-        u8 *ptr = (u8*)(th + 1);
+        int length = (th->doff << 2) - sizeof(*th);
+        const u8 *ptr = (const u8 *)(th + 1);
 
         /* If the TCP option is too short, we can short cut */
         if (length < TCPOLEN_MD5SIG)
@@ -4049,8 +4051,8 @@ static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
 
 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
-        struct tcphdr *th = tcp_hdr(skb);
+        const struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcphdr *th = tcp_hdr(skb);
         u32 seq = TCP_SKB_CB(skb)->seq;
         u32 ack = TCP_SKB_CB(skb)->ack_seq;
 
@@ -4089,7 +4091,7 @@ static inline int tcp_paws_discard(const struct sock *sk,
  * (borrowed from freebsd)
  */
 
-static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
+static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
 {
         return  !before(end_seq, tp->rcv_wup) &&
                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
@@ -4246,7 +4248,7 @@ static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
 }
 
-static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
+static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
@@ -4433,7 +4435,7 @@ static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
 
 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 {
-        struct tcphdr *th = tcp_hdr(skb);
+        const struct tcphdr *th = tcp_hdr(skb);
         struct tcp_sock *tp = tcp_sk(sk);
         int eaten = -1;
 
@@ -4917,9 +4919,9 @@ void tcp_cwnd_application_limited(struct sock *sk)
         tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
-static int tcp_should_expand_sndbuf(struct sock *sk)
+static int tcp_should_expand_sndbuf(const struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
 
         /* If the user specified a specific send buffer setting, do
          * not modify it.
@@ -5028,7 +5030,7 @@ static inline void tcp_ack_snd_check(struct sock *sk)
  *      either form (or just set the sysctl tcp_stdurg).
  */
 
-static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
+static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         u32 ptr = ntohs(th->urg_ptr);
@@ -5094,7 +5096,7 @@ static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
 }
 
 /* This is the 'fast' part of urgent handling. */
-static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
+static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
@@ -5215,9 +5217,9 @@ out:
  * play significant role here.
  */
 static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
-                              struct tcphdr *th, int syn_inerr)
+                              const struct tcphdr *th, int syn_inerr)
 {
-        u8 *hash_location;
+        const u8 *hash_location;
         struct tcp_sock *tp = tcp_sk(sk);
 
         /* RFC1323: H1. Apply PAWS check first. */
@@ -5298,7 +5300,7 @@ discard:
  *      tcp_data_queue when everything is OK.
  */
 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
-                        struct tcphdr *th, unsigned len)
+                        const struct tcphdr *th, unsigned int len)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         int res;
@@ -5509,9 +5511,9 @@ discard:
 EXPORT_SYMBOL(tcp_rcv_established);
 
 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
-                                         struct tcphdr *th, unsigned len)
+                                         const struct tcphdr *th, unsigned int len)
 {
-        u8 *hash_location;
+        const u8 *hash_location;
         struct inet_connection_sock *icsk = inet_csk(sk);
         struct tcp_sock *tp = tcp_sk(sk);
         struct tcp_cookie_values *cvp = tp->cookie_values;
@@ -5786,7 +5788,7 @@ reset_and_undo:
  */
 
 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
-                          struct tcphdr *th, unsigned len)
+                          const struct tcphdr *th, unsigned int len)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct inet_connection_sock *icsk = inet_csk(sk);