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Date:      Thu, 8 Nov 2018 21:58:52 +0000 (UTC)
From:      Glen Barber <gjb@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: r340268 - stable/11/sys/netinet
Message-ID:  <201811082158.wA8Lwqc7093191@repo.freebsd.org>

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Author: gjb
Date: Thu Nov  8 21:58:51 2018
New Revision: 340268
URL: https://svnweb.freebsd.org/changeset/base/340268

Log:
  MFC r340260 (emaste):
   Avoid buffer underwrite in icmp_error
  
   icmp_error allocates either an mbuf (with pkthdr) or a cluster depending
   on the size of data to be quoted in the ICMP reply, but the calculation
   failed to account for the additional padding that m_align may apply.
  
   Include the ip header in the size passed to m_align.  On 64-bit archs
   this will have the net effect of moving everything 4 bytes later in the
   mbuf or cluster.  This will result in slightly pessimal alignment for
   the ICMP data copy.
  
   Also add an assertion that we do not move m_data before the beginning of
   the mbuf or cluster.
  
  Approved by:	re (kib, insta-MFC)
  Security:	CVE-2018-17156
  Sponsored by:	The FreeBSD Foundation

Modified:
  stable/11/sys/netinet/ip_icmp.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/netinet/ip_icmp.c
==============================================================================
--- stable/11/sys/netinet/ip_icmp.c	Thu Nov  8 21:58:23 2018	(r340267)
+++ stable/11/sys/netinet/ip_icmp.c	Thu Nov  8 21:58:51 2018	(r340268)
@@ -310,7 +310,8 @@ stdreply:	icmpelen = max(8, min(V_icmp_quotelen, ntohs
 #endif
 	icmplen = min(icmplen, M_TRAILINGSPACE(m) -
 	    sizeof(struct ip) - ICMP_MINLEN);
-	m_align(m, ICMP_MINLEN + icmplen);
+	m_align(m, sizeof(struct ip) + ICMP_MINLEN + icmplen);
+	m->m_data += sizeof(struct ip);
 	m->m_len = ICMP_MINLEN + icmplen;
 
 	/* XXX MRT  make the outgoing packet use the same FIB
@@ -352,6 +353,8 @@ stdreply:	icmpelen = max(8, min(V_icmp_quotelen, ntohs
 	 * reply should bypass as well.
 	 */
 	m->m_flags |= n->m_flags & M_SKIP_FIREWALL;
+	KASSERT(M_LEADINGSPACE(m) >= sizeof(struct ip),
+	    ("insufficient space for ip header"));
 	m->m_data -= sizeof(struct ip);
 	m->m_len += sizeof(struct ip);
 	m->m_pkthdr.len = m->m_len;



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