tcp: Add tcp_validate_incoming & put duplicated code there

Large block of code duplication removed.

Sadly, the return value thing is a bit tricky here but it
seems the most sensible way to return positive from validator
on success rather than negative.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 69 insertions, 78 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 67ccce2a96bd..e1b15d4e6171 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4691,6 +4691,67 @@ out:
 }
 #endif /* CONFIG_NET_DMA */
 
+/* Does PAWS and seqno based validation of an incoming segment, flags will
+ * play significant role here.
+ */
+static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
+                              struct tcphdr *th, int syn_inerr)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+
+        /* RFC1323: H1. Apply PAWS check first. */
+        if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
+            tcp_paws_discard(sk, skb)) {
+                if (!th->rst) {
+                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
+                        tcp_send_dupack(sk, skb);
+                        goto discard;
+                }
+                /* Reset is accepted even if it did not pass PAWS. */
+        }
+
+        /* Step 1: check sequence number */
+        if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
+                /* RFC793, page 37: "In all states except SYN-SENT, all reset
+                 * (RST) segments are validated by checking their SEQ-fields."
+                 * And page 69: "If an incoming segment is not acceptable,
+                 * an acknowledgment should be sent in reply (unless the RST
+                 * bit is set, if so drop the segment and return)".
+                 */
+                if (!th->rst)
+                        tcp_send_dupack(sk, skb);
+                goto discard;
+        }
+
+        /* Step 2: check RST bit */
+        if (th->rst) {
+                tcp_reset(sk);
+                goto discard;
+        }
+
+        /* ts_recent update must be made after we are sure that the packet
+         * is in window.
+         */
+        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
+        /* step 3: check security and precedence [ignored] */
+
+        /* step 4: Check for a SYN in window. */
+        if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+                if (syn_inerr)
+                        TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
+                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
+                tcp_reset(sk);
+                return -1;
+        }
+
+        return 1;
+
+discard:
+        __kfree_skb(skb);
+        return 0;
+}
+
 /*
  *      TCP receive function for the ESTABLISHED state.
  *
@@ -4718,6 +4779,7 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
                         struct tcphdr *th, unsigned len)
 {
         struct tcp_sock *tp = tcp_sk(sk);
+        int res;
 
         /*
          *      Header prediction.
@@ -4899,51 +4961,12 @@ slow_path:
                 goto csum_error;
 
         /*
-         * RFC1323: H1. Apply PAWS check first.
-         */
-        if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
-            tcp_paws_discard(sk, skb)) {
-                if (!th->rst) {
-                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
-                        tcp_send_dupack(sk, skb);
-                        goto discard;
-                }
-                /* Resets are accepted even if PAWS failed.
-
-                   ts_recent update must be made after we are sure
-                   that the packet is in window.
-                 */
-        }
-
-        /*
          *      Standard slow path.
          */
 
-        if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
-                /* RFC793, page 37: "In all states except SYN-SENT, all reset
-                 * (RST) segments are validated by checking their SEQ-fields."
-                 * And page 69: "If an incoming segment is not acceptable,
-                 * an acknowledgment should be sent in reply (unless the RST bit
-                 * is set, if so drop the segment and return)".
-                 */
-                if (!th->rst)
-                        tcp_send_dupack(sk, skb);
-                goto discard;
-        }
-
-        if (th->rst) {
-                tcp_reset(sk);
-                goto discard;
-        }
-
-        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
-        if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
-                TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
-                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
-                tcp_reset(sk);
-                return 1;
-        }
+        res = tcp_validate_incoming(sk, skb, th, 1);
+        if (res <= 0)
+                return -res;
 
 step5:
         if (th->ack)
@@ -5225,6 +5248,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
         struct tcp_sock *tp = tcp_sk(sk);
         struct inet_connection_sock *icsk = inet_csk(sk);
         int queued = 0;
+        int res;
 
         tp->rx_opt.saw_tstamp = 0;
 
@@ -5277,42 +5301,9 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                 return 0;
         }
 
-        if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
-            tcp_paws_discard(sk, skb)) {
-                if (!th->rst) {
-                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
-                        tcp_send_dupack(sk, skb);
-                        goto discard;
-                }
-                /* Reset is accepted even if it did not pass PAWS. */
-        }
-
-        /* step 1: check sequence number */
-        if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
-                if (!th->rst)
-                        tcp_send_dupack(sk, skb);
-                goto discard;
-        }
-
-        /* step 2: check RST bit */
-        if (th->rst) {
-                tcp_reset(sk);
-                goto discard;
-        }
-
-        tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
-        /* step 3: check security and precedence [ignored] */
-
-        /*      step 4:
-         *
-         *      Check for a SYN in window.
-         */
-        if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
-                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONSYN);
-                tcp_reset(sk);
-                return 1;
-        }
+        res = tcp_validate_incoming(sk, skb, th, 0);
+        if (res <= 0)
+                return -res;
 
         /* step 5: check the ACK field */
         if (th->ack) {