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From: Pedro F. Giffuni <pfg@FreeBSD.org>
Date: Thu, 7 Aug 2014 16:40:24 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r269668 - vendor/resolver/dist/lib/libc/nameser
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Author: pfg
Date: Thu Aug  7 16:40:24 2014
New Revision: 269668
URL: http://svnweb.freebsd.org/changeset/base/269668

Log:
  Fix broken pointer overflow check ns_name_unpack()
  
  Many compilers may optimize away the overflow check `msg + l < msg',
  where `msg' is a pointer and `l' is an integer, because pointer
  overflow is undefined behavior in C.
  
  Use a safe precondition test `l >= eom - msg' instead.
  
  Reference:
  https://android-review.googlesource.com/#/c/50570/
  
  Obtained from:	NetBSD (CVS rev. 1.10)
  MFC after:	3 weeks

Modified:
  vendor/resolver/dist/lib/libc/nameser/ns_name.c

Modified: vendor/resolver/dist/lib/libc/nameser/ns_name.c
==============================================================================
--- vendor/resolver/dist/lib/libc/nameser/ns_name.c	Thu Aug  7 15:56:55 2014	(r269667)
+++ vendor/resolver/dist/lib/libc/nameser/ns_name.c	Thu Aug  7 16:40:24 2014	(r269668)
@@ -461,11 +461,12 @@ ns_name_unpack2(const u_char *msg, const
 			}
 			if (len < 0)
 				len = srcp - src + 1;
-			srcp = msg + (((n & 0x3f) << 8) | (*srcp & 0xff));
-			if (srcp < msg || srcp >= eom) {  /*%< Out of range. */
+			l = ((n & 0x3f) << 8) | (*srcp & 0xff);
+			if (l >= eom - msg) {  /*%< Out of range. */
 				errno = EMSGSIZE;
 				return (-1);
 			}
+			srcp = msg + l;
 			checked += 2;
 			/*
 			 * Check for loops in the compressed name;