svn commit: r298408 - head/sys/netinet

[Jonathan T. Looney]

Author: jtl
Date: Thu Apr 21 15:06:53 2016
New Revision: 298408
URL: https://svnweb.freebsd.org/changeset/base/298408

Log:
  Prevent underflows in tp->snd_wnd if the remote side ACKs more than
  tp->snd_wnd. This can happen, for example, when the remote side responds to
  a window probe by ACKing the one byte it contains.
  
  Differential Revision:	https://reviews.freebsd.org/D5625
  Reviewed by:	hiren
  Obtained from:	Juniper Networks (earlier version)
  MFC after:	2 weeks
  Sponsored by:	Juniper Networks

Modified:
  head/sys/netinet/tcp_input.c

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c	Thu Apr 21 15:02:57 2016	(r298407)
+++ head/sys/netinet/tcp_input.c	Thu Apr 21 15:06:53 2016	(r298408)
@@ -2754,6 +2754,9 @@ process_ACK:
 		INP_WLOCK_ASSERT(tp->t_inpcb);
 
 		acked = BYTES_THIS_ACK(tp, th);
+		KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
+		    "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
+		    tp->snd_una, th->th_ack, tp, m));
 		TCPSTAT_INC(tcps_rcvackpack);
 		TCPSTAT_ADD(tcps_rcvackbyte, acked);
 
@@ -2823,13 +2826,19 @@ process_ACK:
 
 		SOCKBUF_LOCK(&so->so_snd);
 		if (acked > sbavail(&so->so_snd)) {
-			tp->snd_wnd -= sbavail(&so->so_snd);
+			if (tp->snd_wnd >= sbavail(&so->so_snd))
+				tp->snd_wnd -= sbavail(&so->so_snd);
+			else
+				tp->snd_wnd = 0;
 			mfree = sbcut_locked(&so->so_snd,
 			    (int)sbavail(&so->so_snd));
 			ourfinisacked = 1;
 		} else {
 			mfree = sbcut_locked(&so->so_snd, acked);
-			tp->snd_wnd -= acked;
+			if (tp->snd_wnd >= (u_long) acked)
+				tp->snd_wnd -= acked;
+			else
+				tp->snd_wnd = 0;
 			ourfinisacked = 0;
 		}
 		/* NB: sowwakeup_locked() does an implicit unlock. */