1 files changed, 80 insertions, 33 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 6b017383119e..b40e05b9c451 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -88,6 +88,9 @@ int sysctl_tcp_app_win __read_mostly = 31;
 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_stdurg __read_mostly;
 int sysctl_tcp_rfc1337 __read_mostly;
 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
@@ -3037,13 +3040,14 @@ static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
  * tcp_xmit_retransmit_queue().
  */
 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
-				  int newly_acked_sacked, bool is_dupack,
+				  int prior_sacked, bool is_dupack,
 				  int flag)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
 				    (tcp_fackets_out(tp) > tp->reordering));
+	int newly_acked_sacked = 0;
 	int fast_rexmit = 0, mib_idx;
 
 	if (WARN_ON(!tp->packets_out && tp->sacked_out))
@@ -3103,6 +3107,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 				tcp_add_reno_sack(sk);
 		} else
 			do_lost = tcp_try_undo_partial(sk, pkts_acked);
+		newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
 		break;
 	case TCP_CA_Loss:
 		if (flag & FLAG_DATA_ACKED)
@@ -3124,6 +3129,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
 			if (is_dupack)
 				tcp_add_reno_sack(sk);
 		}
+		newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
 
 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
 			tcp_try_undo_dsack(sk);
@@ -3633,6 +3639,11 @@ static int tcp_process_frto(struct sock *sk, int flag)
 		}
 	} else {
 		if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
+			if (!tcp_packets_in_flight(tp)) {
+				tcp_enter_frto_loss(sk, 2, flag);
+				return true;
+			}
+
 			/* Prevent sending of new data. */
 			tp->snd_cwnd = min(tp->snd_cwnd,
 					   tcp_packets_in_flight(tp));
@@ -3681,6 +3692,24 @@ static int tcp_process_frto(struct sock *sk, int flag)
 	return 0;
 }
 
+/* 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)
 {
@@ -3695,14 +3724,19 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	int prior_packets;
 	int prior_sacked = tp->sacked_out;
 	int pkts_acked = 0;
-	int newly_acked_sacked = 0;
 	int frto_cwnd = 0;
 
 	/* 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).
@@ -3768,8 +3802,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
 
 	pkts_acked = prior_packets - tp->packets_out;
-	newly_acked_sacked = (prior_packets - prior_sacked) -
-			     (tp->packets_out - tp->sacked_out);
 
 	if (tp->frto_counter)
 		frto_cwnd = tcp_process_frto(sk, flag);
@@ -3783,7 +3815,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		    tcp_may_raise_cwnd(sk, flag))
 			tcp_cong_avoid(sk, ack, prior_in_flight);
 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
-		tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
 				      is_dupack, flag);
 	} else {
 		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
@@ -3798,7 +3830,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 no_queue:
 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
 	if (flag & FLAG_DSACKING_ACK)
-		tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
 				      is_dupack, flag);
 	/* If this ack opens up a zero window, clear backoff.  It was
 	 * being used to time the probes, and is probably far higher than
@@ -3818,8 +3850,7 @@ old_ack:
 	 */
 	if (TCP_SKB_CB(skb)->sacked) {
 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
-		newly_acked_sacked = tp->sacked_out - prior_sacked;
-		tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+		tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
 				      is_dupack, flag);
 	}
 
@@ -5271,8 +5302,8 @@ out:
 /* 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,
-			      const struct tcphdr *th, int syn_inerr)
+static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
+				  const struct tcphdr *th, int syn_inerr)
 {
 	const u8 *hash_location;
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -5297,38 +5328,48 @@ static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 		 * an acknowledgment should be sent in reply (unless the RST
 		 * bit is set, if so drop the segment and return)".
 		 */
-		if (!th->rst)
+		if (!th->rst) {
+			if (th->syn)
+				goto syn_challenge;
 			tcp_send_dupack(sk, skb);
+		}
 		goto discard;
 	}
 
 	/* Step 2: check RST bit */
 	if (th->rst) {
-		tcp_reset(sk);
+		/* RFC 5961 3.2 :
+		 * If sequence number exactly matches RCV.NXT, then
+		 *     RESET the connection
+		 * else
+		 *     Send a challenge ACK
+		 */
+		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
+			tcp_reset(sk);
+		else
+			tcp_send_challenge_ack(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)) {
+	/* step 4: Check for a SYN
+	 * RFC 5691 4.2 : Send a challenge ack
+	 */
+	if (th->syn) {
+syn_challenge:
 		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;
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
+		tcp_send_challenge_ack(sk);
+		goto discard;
 	}
 
-	return 1;
+	return true;
 
 discard:
 	__kfree_skb(skb);
-	return 0;
+	return false;
 }
 
 /*
@@ -5358,7 +5399,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
 			const struct tcphdr *th, unsigned int len)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	int res;
 
 	/*
 	 *	Header prediction.
@@ -5538,14 +5578,18 @@ slow_path:
 	 *	Standard slow path.
 	 */
 
-	res = tcp_validate_incoming(sk, skb, th, 1);
-	if (res <= 0)
-		return -res;
+	if (!tcp_validate_incoming(sk, skb, th, 1))
+		return 0;
 
 step5:
 	if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
 		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);
+
 	tcp_rcv_rtt_measure_ts(sk, skb);
 
 	/* Process urgent data. */
@@ -5850,7 +5894,6 @@ 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;
 
@@ -5905,9 +5948,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 		return 0;
 	}
 
-	res = tcp_validate_incoming(sk, skb, th, 0);
-	if (res <= 0)
-		return -res;
+	if (!tcp_validate_incoming(sk, skb, th, 0))
+		return 0;
 
 	/* step 5: check the ACK field */
 	if (th->ack) {
@@ -6018,6 +6060,11 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 	} else
 		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 6: check the URG bit */
 	tcp_urg(sk, skb, th);