NSS: add `balloon' extension to when we might hit the F5 bug.

net/third_party/nss/ssl/ssl3ext.c

 /*
  * SSL3 Protocol
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /* TLS extension code moved here from ssl3ecc.c */
 
 #include "nssrenam.h"
@@ skipping 2279 matching lines @@
     } else if (maxBytes < extension_length) {
         PORT_Assert(0);
         return 0;
     }
 
     return extension_length;
 
 loser:
     return -1;
 }
+
+unsigned int
+ssl3_CalculatePaddingExtensionLength(unsigned int clientHelloLength)
+{
+    unsigned int recordLength = 1 /* handshake message type */ +
+                                3 /* handshake message length */ +
+                                clientHelloLength;
+    unsigned int extensionLength;
+
+    if (recordLength < 256 || recordLength >= 512) {
+        return 0;
+    }
+
+     extensionLength = 512 - recordLength;
+     /* Extensions take at least four bytes to encode. */
+     if (extensionLength < 4) {
+         extensionLength = 4;
+     }
+
+     return extensionLength;
+}
+
+/* ssl3_AppendPaddingExtension possibly adds an extension which ensures that a
+ * ClientHello record is either < 256 bytes or is >= 512 bytes. This ensures
+ * that we don't trigger bugs in F5 products. */
+unsigned int
+ssl3_AppendPaddingExtension(sslSocket *ss, unsigned int extensionLen,
+                            PRUint32 maxBytes)
+{
+    SECStatus rv;
+    unsigned int paddingLen = extensionLen - 4;
+    unsigned char padding[256];
+
+    if (extensionLen == 0) {
+        return 0;
+    }
+
+    if (extensionLen < 4 ||
+        extensionLen > maxBytes ||
+        paddingLen > sizeof(padding)) {
+        PORT_Assert(0);
+        return 0;
+    }
+
+    if (SECSuccess != ssl3_AppendHandshakeNumber(ss, ssl_padding_xtn, 2))

[wtc, 2013/11/08 20:10:06]

Nit: just curious why you use the SECSuccess != Foo() form. This style isn't
required in NSS.

[agl, 2013/11/08 20:33:23]

I've been reviewing code from thaidn this morning and he uses it a lot :)

+        return -1;
+    if (SECSuccess != ssl3_AppendHandshakeNumber(ss, paddingLen, 2))
+        return -1;
+    memset(padding, ' ', paddingLen);
+    if (SECSuccess != ssl3_AppendHandshake(ss, padding, paddingLen))
+        return -1;
+
+    return extensionLen;
+}