Reorder cleanup sequence in SSL_CTX_free() to leave ex_data for remove_cb().

Submitted by:
Reviewed by:
PR: 212

CHANGES

@@ -1914,6 +1914,12 @@ des-cbc           3624.96k     5258.21k     5530.91k     5624.30k     5628.26k
 
  Changes between 0.9.6g and 0.9.6h  [xx XXX xxxx]
 
+  *) Reorder cleanup sequence in SSL_CTX_free(): only remove the ex_data after
+     the cached sessions are flushed, as the remove_cb() might use ex_data
+     contents. Bug found by Sam Varshavchik <mrsam@courier-mta.com>
+     (see [openssl.org #212]).
+     [Geoff Thorpe, Lutz Jaenicke]
+
   *) Fix typo in OBJ_txt2obj which incorrectly passed the content
      length, instead of the encoding length to d2i_ASN1_OBJECT.
      [Steve Henson]

ssl/ssl_lib.c

@@ -1409,13 +1409,24 @@ void SSL_CTX_free(SSL_CTX *a)
 		abort(); /* ok */
 		}
 #endif
-	CRYPTO_free_ex_data(CRYPTO_EX_INDEX_SSL_CTX, a, &a->ex_data);
 
+	/*
+	 * Free internal session cache. However: the remove_cb() may reference
+	 * the ex_data of SSL_CTX, thus the ex_data store can only be removed
+	 * after the sessions were flushed.
+	 * As the ex_data handling routines might also touch the session cache,
+	 * the most secure solution seems to be: empty (flush) the cache, then
+	 * free ex_data, then finally free the cache.
+	 * (See ticket [openssl.org #212].)
+	 */
 	if (a->sessions != NULL)
-		{
 		SSL_CTX_flush_sessions(a,0);
+
+	CRYPTO_free_ex_data(CRYPTO_EX_INDEX_SSL_CTX, a, &a->ex_data);
+
+	if (a->sessions != NULL)
 		lh_free(a->sessions);
-		}
+
 	if (a->cert_store != NULL)
 		X509_STORE_free(a->cert_store);
 	if (a->cipher_list != NULL)