5 files changed, 31 insertions, 9 deletions

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 49daaed89764..f687abb069fa 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -490,6 +490,7 @@ static struct xfrm_tunnel vti_ipip_handler __read_mostly = {
 	.priority	=	0,
 };
 
+#if IS_ENABLED(CONFIG_IPV6)
 static struct xfrm_tunnel vti_ipip6_handler __read_mostly = {
 	.handler	=	vti_rcv_tunnel,
 	.cb_handler	=	vti_rcv_cb,
@@ -497,6 +498,7 @@ static struct xfrm_tunnel vti_ipip6_handler __read_mostly = {
 	.priority	=	0,
 };
 #endif
+#endif
 
 static int __net_init vti_init_net(struct net *net)
 {
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 1074df726ec0..8d5e1695b9aa 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -293,6 +293,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TcpTimeoutRehash", LINUX_MIB_TCPTIMEOUTREHASH),
 	SNMP_MIB_ITEM("TcpDuplicateDataRehash", LINUX_MIB_TCPDUPLICATEDATAREHASH),
 	SNMP_MIB_ITEM("TCPDSACKRecvSegs", LINUX_MIB_TCPDSACKRECVSEGS),
+	SNMP_MIB_ITEM("TCPDSACKIgnoredDubious", LINUX_MIB_TCPDSACKIGNOREDDUBIOUS),
 	SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index f0794f0232ba..e03756631541 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -214,7 +214,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 		sock_rps_save_rxhash(child, skb);
 
 		if (rsk_drop_req(req)) {
-			refcount_set(&req->rsk_refcnt, 2);
+			reqsk_put(req);
 			return child;
 		}
 
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 31f3b858db81..2135ee7c806d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -970,7 +970,8 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
 	long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
 
 	if (IS_ENABLED(CONFIG_DEBUG_VM) &&
-	    WARN_ONCE(PageSlab(page), "page must not be a Slab one"))
+	    WARN_ONCE(!sendpage_ok(page),
+		      "page must not be a Slab one and have page_count > 0"))
 		return -EINVAL;
 
 	/* Wait for a connection to finish. One exception is TCP Fast Open
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 184ea556f50e..b1ce2054291d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -885,21 +885,34 @@ struct tcp_sacktag_state {
 	struct rate_sample *rate;
 };
 
-/* Take a notice that peer is sending D-SACKs */
+/* Take a notice that peer is sending D-SACKs. Skip update of data delivery
+ * and spurious retransmission information if this DSACK is unlikely caused by
+ * sender's action:
+ * - DSACKed sequence range is larger than maximum receiver's window.
+ * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
+ */
 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
 			  u32 end_seq, struct tcp_sacktag_state *state)
 {
 	u32 seq_len, dup_segs = 1;
 
-	if (before(start_seq, end_seq)) {
-		seq_len = end_seq - start_seq;
-		if (seq_len > tp->mss_cache)
-			dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
-	}
+	if (!before(start_seq, end_seq))
+		return 0;
+
+	seq_len = end_seq - start_seq;
+	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
+	if (seq_len > tp->max_window)
+		return 0;
+	if (seq_len > tp->mss_cache)
+		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
+
+	tp->dsack_dups += dup_segs;
+	/* Skip the DSACK if dup segs weren't retransmitted by sender */
+	if (tp->dsack_dups > tp->total_retrans)
+		return 0;
 
 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
 	tp->rack.dsack_seen = 1;
-	tp->dsack_dups += dup_segs;
 
 	state->flag |= FLAG_DSACKING_ACK;
 	/* A spurious retransmission is delivered */
@@ -1153,6 +1166,11 @@ static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
 	}
 
 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
+	if (!dup_segs) {	/* Skip dubious DSACK */
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
+		return false;
+	}
+
 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
 
 	/* D-SACK for already forgotten data... Do dumb counting. */