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From: "Bjoern A. Zeeb" <bz@FreeBSD.org>
Date: Fri, 31 Dec 2010 21:47:11 +0000 (UTC)
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Subject: svn commit: r216857 - head/sys/netinet
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Author: bz
Date: Fri Dec 31 21:47:11 2010
New Revision: 216857
URL: http://svn.freebsd.org/changeset/base/216857

Log:
  Try to catch a possible divide-by-zero as early as possible if "mtu" is 0
  (also test for negative MTUs if checking it anyway).
  An MTU of 0 is arguably a bug elsewhere, but this at least gives us some
  more debugging hints.
  
  Sponsored by:	ISPsystem (Early 2010)
  MFC after:	1 week

Modified:
  head/sys/netinet/ip_output.c

Modified: head/sys/netinet/ip_output.c
==============================================================================
--- head/sys/netinet/ip_output.c	Fri Dec 31 21:20:32 2010	(r216856)
+++ head/sys/netinet/ip_output.c	Fri Dec 31 21:47:11 2010	(r216857)
@@ -323,6 +323,9 @@ again:
 	} else {
 		mtu = ifp->if_mtu;
 	}
+	/* Catch a possible divide by zero later. */
+	KASSERT(mtu > 0, ("%s: mtu %d <= 0, rte=%p (rt_flags=0x%08x) ifp=%p",
+	    __func__, mtu, rte, (rte != NULL) ? rte->rt_flags : 0, ifp));
 	if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
 		m->m_flags |= M_MCAST;
 		/*