svn commit: r299147 - stable/9/sys/netinet

[Jonathan T. Looney]

Author: jtl
Date: Fri May  6 01:27:01 2016
New Revision: 299147
URL: https://svnweb.freebsd.org/changeset/base/299147

Log:
  MFC r298408:
    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.

Modified:
  stable/9/sys/netinet/tcp_input.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/netinet/tcp_input.c
==============================================================================
--- stable/9/sys/netinet/tcp_input.c	Fri May  6 01:26:58 2016	(r299146)
+++ stable/9/sys/netinet/tcp_input.c	Fri May  6 01:27:01 2016	(r299147)
@@ -2629,6 +2629,9 @@ 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);
 
@@ -2698,12 +2701,18 @@ process_ACK:
 
 		SOCKBUF_LOCK(&so->so_snd);
 		if (acked > so->so_snd.sb_cc) {
-			tp->snd_wnd -= so->so_snd.sb_cc;
+			if (tp->snd_wnd >= so->so_snd.sb_cc)
+				tp->snd_wnd -= so->so_snd.sb_cc;
+			else
+				tp->snd_wnd = 0;
 			sbdrop_locked(&so->so_snd, (int)so->so_snd.sb_cc);
 			ourfinisacked = 1;
 		} else {
 			sbdrop_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. */