1 files changed, 32 insertions, 22 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 94d4aff97523..f9f9e375d7de 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -87,7 +87,7 @@ int sysctl_tcp_adv_win_scale __read_mostly = 1;
 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
 
 /* rfc5961 challenge ack rate limiting */
-int sysctl_tcp_challenge_ack_limit = 100;
+int sysctl_tcp_challenge_ack_limit = 1000;
 
 int sysctl_tcp_stdurg __read_mostly;
 int sysctl_tcp_rfc1337 __read_mostly;
@@ -3424,6 +3424,23 @@ static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32
         return flag;
 }
 
+static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
+                                   u32 *last_oow_ack_time)
+{
+        if (*last_oow_ack_time) {
+                s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
+
+                if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
+                        NET_INC_STATS(net, mib_idx);
+                        return true;    /* rate-limited: don't send yet! */
+                }
+        }
+
+        *last_oow_ack_time = tcp_time_stamp;
+
+        return false;   /* not rate-limited: go ahead, send dupack now! */
+}
+
 /* Return true if we're currently rate-limiting out-of-window ACKs and
  * thus shouldn't send a dupack right now. We rate-limit dupacks in
  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
@@ -3437,21 +3454,9 @@ bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
         /* Data packets without SYNs are not likely part of an ACK loop. */
         if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
             !tcp_hdr(skb)->syn)
-                goto not_rate_limited;
-
-        if (*last_oow_ack_time) {
-                s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
-
-                if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
-                        NET_INC_STATS(net, mib_idx);
-                        return true;    /* rate-limited: don't send yet! */
-                }
-        }
-
-        *last_oow_ack_time = tcp_time_stamp;
+                return false;
 
-not_rate_limited:
-        return false;   /* not rate-limited: go ahead, send dupack now! */
+        return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
 }
 
 /* RFC 5961 7 [ACK Throttling] */
@@ -3461,21 +3466,26 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
         static u32 challenge_timestamp;
         static unsigned int challenge_count;
         struct tcp_sock *tp = tcp_sk(sk);
-        u32 now;
+        u32 count, now;
 
         /* First check our per-socket dupack rate limit. */
-        if (tcp_oow_rate_limited(sock_net(sk), skb,
-                                 LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
-                                 &tp->last_oow_ack_time))
+        if (__tcp_oow_rate_limited(sock_net(sk),
+                                   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
+                                   &tp->last_oow_ack_time))
                 return;
 
-        /* Then check the check host-wide RFC 5961 rate limit. */
+        /* Then check host-wide RFC 5961 rate limit. */
         now = jiffies / HZ;
         if (now != challenge_timestamp) {
+                u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;
+
                 challenge_timestamp = now;
-                challenge_count = 0;
+                WRITE_ONCE(challenge_count, half +
+                           prandom_u32_max(sysctl_tcp_challenge_ack_limit));
         }
-        if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
+        count = READ_ONCE(challenge_count);
+        if (count > 0) {
+                WRITE_ONCE(challenge_count, count - 1);
                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
                 tcp_send_ack(sk);
         }