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Date:      Thu, 1 Jun 2017 14:58:26 +0000 (UTC)
From:      Michael Tuexen <tuexen@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org
Subject:   svn commit: r319431 - in stable/11/sys/netinet: . tcp_stacks
Message-ID:  <201706011458.v51EwQ3v082894@repo.freebsd.org>
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Author: tuexen
Date: Thu Jun  1 14:58:26 2017
New Revision: 319431
URL: https://svnweb.freebsd.org/changeset/base/319431

Log:
  When a SYN-ACK is received in SYN-SENT state, RFC 793 requires the
  validation of SEG.ACK as the first step. If the ACK is not acceptable,
  a RST segment should be sent and the segment should be dropped.
  Up to now, the segment was partially processed.
  This patch moves the check for the SEG.ACK validation up to the front
  as required.
  
  Reviewed by:		hiren, gnn
  Differential Revision:	https://reviews.freebsd.org/D10424

Modified:
  stable/11/sys/netinet/tcp_input.c
  stable/11/sys/netinet/tcp_stacks/fastpath.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/netinet/tcp_input.c
==============================================================================
--- stable/11/sys/netinet/tcp_input.c	Thu Jun  1 14:49:53 2017	(r319430)
+++ stable/11/sys/netinet/tcp_input.c	Thu Jun  1 14:58:26 2017	(r319431)
@@ -1607,6 +1607,16 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
 	}
 
 	/*
+	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
+	 * check SEQ.ACK first.
+	 */
+	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
+	    (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
+		rstreason = BANDLIM_UNLIMITED;
+		goto dropwithreset;
+	}
+
+	/*
 	 * Segment received on connection.
 	 * Reset idle time and keep-alive timer.
 	 * XXX: This should be done after segment
@@ -1984,7 +1994,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
 
 	/*
 	 * If the state is SYN_SENT:
-	 *	if seg contains an ACK, but not for our SYN, drop the input.
 	 *	if seg contains a RST, then drop the connection.
 	 *	if seg does not contain SYN, then drop it.
 	 * Otherwise this is an acceptable SYN segment
@@ -1997,12 +2006,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru
 	 *	continue processing rest of data/controls, beginning with URG
 	 */
 	case TCPS_SYN_SENT:
-		if ((thflags & TH_ACK) &&
-		    (SEQ_LEQ(th->th_ack, tp->iss) ||
-		     SEQ_GT(th->th_ack, tp->snd_max))) {
-			rstreason = BANDLIM_UNLIMITED;
-			goto dropwithreset;
-		}
 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 			TCP_PROBE5(connect__refused, NULL, tp,
 			    m, tp, th);

Modified: stable/11/sys/netinet/tcp_stacks/fastpath.c
==============================================================================
--- stable/11/sys/netinet/tcp_stacks/fastpath.c	Thu Jun  1 14:49:53 2017	(r319430)
+++ stable/11/sys/netinet/tcp_stacks/fastpath.c	Thu Jun  1 14:58:26 2017	(r319431)
@@ -485,7 +485,6 @@ tcp_do_slowpath(struct mbuf *m, struct tcphdr *th, str
 
 	/*
 	 * If the state is SYN_SENT:
-	 *	if seg contains an ACK, but not for our SYN, drop the input.
 	 *	if seg contains a RST, then drop the connection.
 	 *	if seg does not contain SYN, then drop it.
 	 * Otherwise this is an acceptable SYN segment
@@ -498,12 +497,6 @@ tcp_do_slowpath(struct mbuf *m, struct tcphdr *th, str
 	 *	continue processing rest of data/controls, beginning with URG
 	 */
 	case TCPS_SYN_SENT:
-		if ((thflags & TH_ACK) &&
-		    (SEQ_LEQ(th->th_ack, tp->iss) ||
-		     SEQ_GT(th->th_ack, tp->snd_max))) {
-			rstreason = BANDLIM_UNLIMITED;
-			goto dropwithreset;
-		}
 		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
 			TCP_PROBE5(connect__refused, NULL, tp, m, tp, th);
 			tp = tcp_drop(tp, ECONNREFUSED);
@@ -1744,6 +1737,20 @@ tcp_do_segment_fastslow(struct mbuf *m, struct tcphdr 
 		m_freem(m);
 		return;
 	}
+	
+	/*
+	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
+	 * check SEQ.ACK first.
+	 */
+	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
+	    (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
+		tcp_dropwithreset(m, th, tp, tlen, BANDLIM_UNLIMITED);
+		if (ti_locked == TI_RLOCKED) {
+			INP_INFO_RUNLOCK(&V_tcbinfo);
+		}
+		INP_WUNLOCK(tp->t_inpcb);
+		return;
+	}
 
 	tp->sackhint.last_sack_ack = 0;
 
@@ -2203,6 +2210,20 @@ tcp_do_segment_fastack(struct mbuf *m, struct tcphdr *
 		return;
 	}
 
+	/*
+	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
+	 * check SEQ.ACK first.
+	 */
+	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
+	    (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
+		tcp_dropwithreset(m, th, tp, tlen, BANDLIM_UNLIMITED);
+		if (ti_locked == TI_RLOCKED) {
+			INP_INFO_RUNLOCK(&V_tcbinfo);
+		}
+		INP_WUNLOCK(tp->t_inpcb);
+		return;
+	}
+	
 	tp->sackhint.last_sack_ack = 0;
 
 	/*

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