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From: Andre Oppermann <andre@FreeBSD.org>
Date: Tue, 9 Apr 2013 20:52:26 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r249317 - head/sys/netinet
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Author: andre
Date: Tue Apr  9 20:52:26 2013
New Revision: 249317
URL: http://svnweb.freebsd.org/changeset/base/249317

Log:
  Fix a race condition on tcp listen socket teardown with pending
  connections in the accept queue and contiguous new incoming SYNs.
  
  Compared to the original submitters patch I've moved the test
  next to the SYN handling to have it together in a logical unit
  and reworded the comment explaining the issue.
  
  Submitted by:	Matt Miller <matt@matthewjmiller.net>
  Submitted by:	Juan Mojica <jmojica@gmail.com>
  Reviewed by:	Matt Miller (changes)
  Tested by:	pho
  MFC after:	1 week

Modified:
  head/sys/netinet/tcp_input.c

Modified: head/sys/netinet/tcp_input.c
==============================================================================
--- head/sys/netinet/tcp_input.c	Tue Apr  9 20:21:35 2013	(r249316)
+++ head/sys/netinet/tcp_input.c	Tue Apr  9 20:52:26 2013	(r249317)
@@ -1405,6 +1405,15 @@ relocked:
 		 */
 		INP_INFO_UNLOCK_ASSERT(&V_tcbinfo);
 		return;
+	} else if (tp->t_state == TCPS_LISTEN) {
+		/*
+		 * When a listen socket is torn down the SO_ACCEPTCONN
+		 * flag is removed first while connections are drained
+		 * from the accept queue in a unlock/lock cycle of the
+		 * ACCEPT_LOCK, opening a race condition allowing a SYN
+		 * attempt go through unhandled.
+		 */
+		goto dropunlock;
 	}
 
 #ifdef TCP_SIGNATURE