1 files changed, 26 insertions, 19 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 181fc8234a52..a13692560e63 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.
  */
@@ -5992,7 +5999,7 @@ 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 {