radclient and Message-Authenticator validation

[Jouni Malinen]

It looks like the Message-Authenticator validation done by radclient for
Disconnect-ACK/NAK and CoA-ACK/NAK messages does not match with the
mechanism described in RFC 5176. Message-Authenticator is generated
correctly for Disconnect-Request and CoA-Request, but I needed to modify
rad_verify() to get this matching with the code I'm writing for hostapd.

RFC 5176, 3.4:

      When a Message-Authenticator Attribute is included within a CoA-
      ACK, CoA-NAK, Disconnect-ACK, or Disconnect-NAK, it is calculated
      as follows:

         Message-Authenticator = HMAC-MD5 (Type, Identifier, Length,
         Request Authenticator, Attributes)

      When the HMAC-MD5 message integrity check is calculated, the
      Message-Authenticator Attribute MUST be considered to be sixteen
      octets of zero.  The Request Authenticator is taken from the
      corresponding CoA/Disconnect-Request.  The Message-Authenticator
      is calculated and inserted in the packet before the Response
      Authenticator is calculated.


It is that "The Request Authenticator is taken from the corresponding
CoA/Disconnect-Request" part that does not seem to be followed by the
current rad_verify() implementation. It clears the Authenticator field
to all zeros (which is the mechanism used for the Request message)
instead of using the Authenticator field from the Request message when
validating the ACK/NAK message. Is this a workaround for some deployed
NAS implementations or can this be fixed to match with RFC 5176?

The following change was enough to make this interoperate with my
hostapd implementation.


diff --git a/src/lib/radius.c b/src/lib/radius.c
index 7025573..dec3849 100644
--- a/src/lib/radius.c
+++ b/src/lib/radius.c
@@ -2619,11 +2619,7 @@ int rad_verify(RADIUS_PACKET *packet, RADIUS_PACKET *original,
 
 			case PW_ACCOUNTING_REQUEST:
 			case PW_DISCONNECT_REQUEST:
-			case PW_DISCONNECT_ACK:
-			case PW_DISCONNECT_NAK:
 			case PW_COA_REQUEST:
-			case PW_COA_ACK:
-			case PW_COA_NAK:
 			  	memset(packet->data + 4, 0, AUTH_VECTOR_LEN);
 				break;
 
@@ -2631,6 +2627,10 @@ int rad_verify(RADIUS_PACKET *packet, RADIUS_PACKET *original,
 			case PW_AUTHENTICATION_ACK:
 			case PW_AUTHENTICATION_REJECT:
 			case PW_ACCESS_CHALLENGE:
+			case PW_DISCONNECT_ACK:
+			case PW_DISCONNECT_NAK:
+			case PW_COA_ACK:
+			case PW_COA_NAK:
 				if (!original) {
 					fr_strerror_printf("ERROR: Cannot validate Message-Authenticator in response packet without a request packet.");
 					return -1;


-- 
Jouni Malinen                                            PGP id EFC895FA