1 files changed, 36 insertions, 23 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 181fc8234a52..18f97ca76b00 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3552,6 +3552,24 @@ static bool tcp_process_frto(struct sock *sk, int flag)
         return false;
 }
 
+/* RFC 5961 7 [ACK Throttling] */
+static void tcp_send_challenge_ack(struct sock *sk)
+{
+        /* unprotected vars, we dont care of overwrites */
+        static u32 challenge_timestamp;
+        static unsigned int challenge_count;
+        u32 now = jiffies / HZ;
+
+        if (now != challenge_timestamp) {
+                challenge_timestamp = now;
+                challenge_count = 0;
+        }
+        if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
+                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+                tcp_send_ack(sk);
+        }
+}
+
 /* This routine deals with incoming acks, but not outgoing ones. */
 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 {
@@ -3571,8 +3589,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
         /* If the ack is older than previous acks
          * then we can probably ignore it.
          */
-        if (before(ack, prior_snd_una))
+        if (before(ack, prior_snd_una)) {
+                /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
+                if (before(ack, prior_snd_una - tp->max_window)) {
+                        tcp_send_challenge_ack(sk);
+                        return -1;
+                }
                 goto old_ack;
+        }
 
         /* If the ack includes data we haven't sent yet, discard
          * this segment (RFC793 Section 3.9).
@@ -5244,23 +5268,6 @@ out:
 }
 #endif /* CONFIG_NET_DMA */
 
-static void tcp_send_challenge_ack(struct sock *sk)
-{
-        /* unprotected vars, we dont care of overwrites */
-        static u32 challenge_timestamp;
-        static unsigned int challenge_count;
-        u32 now = jiffies / HZ;
-
-        if (now != challenge_timestamp) {
-                challenge_timestamp = now;
-                challenge_count = 0;
-        }
-        if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
-                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
-                tcp_send_ack(sk);
-        }
-}
-
 /* Does PAWS and seqno based validation of an incoming segment, flags will
  * play significant role here.
  */
@@ -5536,6 +5543,9 @@ slow_path:
         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
                 goto csum_error;
 
+        if (!th->ack && !th->rst)
+                goto discard;
+
         /*
          *      Standard slow path.
          */
@@ -5544,7 +5554,7 @@ slow_path:
                 return 0;
 
 step5:
-        if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
+        if (tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
                 goto discard;
 
         /* ts_recent update must be made after we are sure that the packet
@@ -5977,11 +5987,15 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                 if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
                         goto discard;
         }
+
+        if (!th->ack && !th->rst)
+                goto discard;
+
         if (!tcp_validate_incoming(sk, skb, th, 0))
                 return 0;
 
         /* step 5: check the ACK field */
-        if (th->ack) {
+        if (true) {
                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH) > 0;
 
                 switch (sk->sk_state) {
@@ -5992,7 +6006,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                                  */
                                 if (req) {
                                         tcp_synack_rtt_meas(sk, req);
-                                        tp->total_retrans = req->retrans;
+                                        tp->total_retrans = req->num_retrans;
 
                                         reqsk_fastopen_remove(sk, req, false);
                                 } else {
@@ -6131,8 +6145,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                         }
                         break;
                 }
-        } else
-                goto discard;
+        }
 
         /* ts_recent update must be made after we are sure that the packet
          * is in window.