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From: Jaakko Heinonen <jh@FreeBSD.org>
Date: Wed, 3 Mar 2010 15:43:27 +0000 (UTC)
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Subject: svn commit: r204636 - head/lib/libc/stdlib
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Author: jh
Date: Wed Mar  3 15:43:26 2010
New Revision: 204636
URL: http://svn.freebsd.org/changeset/base/204636

Log:
  In reallocf(3), free the memory only when size != 0. Otherwise, when the
  System V compatibility option (malloc "V" flag) is in effect a zero sized
  reallocf() could cause a double free.
  
  PR:		bin/141753
  Submitted by:	Dan Lukes

Modified:
  head/lib/libc/stdlib/reallocf.c

Modified: head/lib/libc/stdlib/reallocf.c
==============================================================================
--- head/lib/libc/stdlib/reallocf.c	Wed Mar  3 15:05:58 2010	(r204635)
+++ head/lib/libc/stdlib/reallocf.c	Wed Mar  3 15:43:26 2010	(r204636)
@@ -35,7 +35,14 @@ reallocf(void *ptr, size_t size)
 	void *nptr;
 
 	nptr = realloc(ptr, size);
-	if (!nptr && ptr)
+
+	/*
+	 * When the System V compatibility option (malloc "V" flag) is
+	 * in effect, realloc(ptr, 0) frees the memory and returns NULL.
+	 * So, to avoid double free, call free() only when size != 0.
+	 * realloc(ptr, 0) can't fail when ptr != NULL.
+	 */
+	if (!nptr && ptr && size != 0)
 		free(ptr);
 	return (nptr);
 }