diff --git a/CHANGES b/CHANGES
index e94951809e..736228a091 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,8 @@
+2547.	[bug]		openssl_link.c:mem_realloc() could reference an
+			out-of-range area of the source buffer.  New public
+			function isc_mem_reallocate() was introduced to address
+			this bug. [RT #19313]
+
 2546.	[func]		Add --enable-openssl-hash configure flag to use
 			OpenSSL (in place of internal routine) for hash
 			functions (MD5, SHA[12] and HMAC). [RT #18815]
diff --git a/lib/dns/openssl_link.c b/lib/dns/openssl_link.c
index a66be2cbed..41e9e2f512 100644
--- a/lib/dns/openssl_link.c
+++ b/lib/dns/openssl_link.c
@@ -31,7 +31,7 @@
 
 /*
  * Principal Author: Brian Wellington
- * $Id: openssl_link.c,v 1.24 2009/01/17 23:47:42 tbox Exp $
+ * $Id: openssl_link.c,v 1.25 2009/02/11 03:04:18 jinmei Exp $
  */
 #ifdef OPENSSL
 
@@ -148,18 +148,8 @@ mem_free(void *ptr) {
 
 static void *
 mem_realloc(void *ptr, size_t size) {
-	void *p;
-
 	INSIST(dst__memory_pool != NULL);
-	p = NULL;
-	if (size > 0U) {
-		p = mem_alloc(size);
-		if (p != NULL && ptr != NULL)
-			memcpy(p, ptr, size);
-	}
-	if (ptr != NULL)
-		mem_free(ptr);
-	return (p);
+	return (isc_mem_reallocate(dst__memory_pool, ptr, size));
 }
 
 isc_result_t
diff --git a/lib/isc/include/isc/mem.h b/lib/isc/include/isc/mem.h
index 8af12a1cd4..a114d3eb6a 100644
--- a/lib/isc/include/isc/mem.h
+++ b/lib/isc/include/isc/mem.h
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: mem.h,v 1.80 2009/01/17 23:47:43 tbox Exp $ */
+/* $Id: mem.h,v 1.81 2009/02/11 03:04:18 jinmei Exp $ */
 
 #ifndef ISC_MEM_H
 #define ISC_MEM_H 1
@@ -154,6 +154,7 @@ LIBISC_EXTERNAL_DATA extern unsigned int isc_mem_debugging;
 
 #define isc_mem_get(c, s)	isc__mem_get((c), (s) _ISC_MEM_FILELINE)
 #define isc_mem_allocate(c, s)	isc__mem_allocate((c), (s) _ISC_MEM_FILELINE)
+#define isc_mem_reallocate(c, p, s) isc__mem_reallocate((c), (p), (s) _ISC_MEM_FILELINE)
 #define isc_mem_strdup(c, p)	isc__mem_strdup((c), (p) _ISC_MEM_FILELINE)
 #define isc_mempool_get(c)	isc__mempool_get((c) _ISC_MEM_FILELINE)
 
@@ -612,6 +613,8 @@ void
 isc__mem_put(isc_mem_t *, void *, size_t _ISC_MEM_FLARG);
 void *
 isc__mem_allocate(isc_mem_t *, size_t _ISC_MEM_FLARG);
+void *
+isc__mem_reallocate(isc_mem_t *, void *, size_t _ISC_MEM_FLARG);
 void
 isc__mem_free(isc_mem_t *, void * _ISC_MEM_FLARG);
 char *
diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index a427099876..318bc7f8a2 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -15,7 +15,7 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: mem.c,v 1.147 2009/01/22 23:47:54 tbox Exp $ */
+/* $Id: mem.c,v 1.148 2009/02/11 03:04:18 jinmei Exp $ */
 
 /*! \file */
 
@@ -1365,6 +1365,40 @@ isc__mem_allocate(isc_mem_t *ctx, size_t size FLARG) {
 	return (si);
 }
 
+void *
+isc__mem_reallocate(isc_mem_t *ctx, void *ptr, size_t size FLARG) {
+	void *new_ptr = NULL;
+	size_t oldsize, copysize;
+
+	REQUIRE(VALID_CONTEXT(ctx));
+
+	/*
+	 * This function emulates the realloc(3) standard library function:
+	 * - if size > 0, allocate new memory; and if ptr is non NULL, copy
+	 *   as much of the old contents to the new buffer and free the old one.
+	 *   Note that when allocation fails the original pointer is intact;
+	 *   the caller must free it.
+	 * - if size is 0 and ptr is non NULL, simply free the given ptr.
+	 * - this function returns:
+	 *     pointer to the newly allocated memory, or
+	 *     NULL if allocation fails or doesn't happen.
+	 */
+	if (size > 0U) {
+		new_ptr = isc__mem_allocate(ctx, size FLARG_PASS);
+		if (new_ptr != NULL && ptr != NULL) {
+			oldsize = (((size_info *)ptr)[-1]).u.size;
+			INSIST(oldsize >= ALIGNMENT_SIZE);
+			oldsize -= ALIGNMENT_SIZE;
+			copysize = oldsize > size ? size : oldsize;
+			memcpy(new_ptr, ptr, copysize);
+			isc__mem_free(ctx, ptr FLARG_PASS);
+		}
+	} else if (ptr != NULL)
+		isc__mem_free(ctx, ptr FLARG_PASS);
+
+	return (new_ptr);
+}
+
 void
 isc__mem_free(isc_mem_t *ctx, void *ptr FLARG) {
 	size_info *si;