Compensate for dodgy Win98/WinME MSCHAPv2 responses later in the code

path... after we've talked to any RADIUS servers involved, so that we
haven't touched the data before it gets to the server.

Make it clearer in the code that this compensation is done by setting
a flag to a value of zero, a flag which rfc2759 says *MUST* be zero.

While we're here, don't bother passing the peer challenge into
radius_Authenticate().  It's already part of the key we're passing in
(this becomes obvious now that I've structured that data...).

This ``fix'' doesn't help to authenticate Win98/WinME users in my test
environment as ports/net/freeradius seems to ignore the flag
completely anyway, but it may help with other RADIUS servers.

usr.sbin/ppp/chap.c

@@ -761,19 +761,13 @@ chap_Input(struct bundle *bundle, struct link *l, struct mbuf *bp)
           m_freem(bp);
           return NULL;
         }
-        if ((ans = malloc(alen + 2)) == NULL) {
+        if ((ans = malloc(alen + 1)) == NULL) {
           log_Printf(LogERROR, "Chap Input: Out of memory !\n");
           m_freem(bp);
           return NULL;
         }
         *ans = chap->auth.id;
         bp = mbuf_Read(bp, ans + 1, alen);
-        if (p->link.lcp.want_authtype == 0x81 && ans[alen] != '\0') {
-          log_Printf(LogWARN, "%s: Compensating for corrupt (Win98/WinME?) "
-                     "CHAP81 RESPONSE\n", l->name);
-          ans[alen] = '\0';
-        }
-        ans[alen+1] = '\0';
         bp = auth_ReadName(&chap->auth, bp, len);
 #ifndef NODES
         lanman = p->link.lcp.want_authtype == 0x80 &&
@@ -847,8 +841,11 @@ chap_Input(struct bundle *bundle, struct link *l, struct mbuf *bp)
         nlen = strlen(name);
 #ifndef NODES
         if (p->link.lcp.want_authtype == 0x81) {
-          chap->challenge.peer[0] = CHAP81_CHALLENGE_LEN;
-          memcpy(chap->challenge.peer + 1, ans + 1, CHAP81_CHALLENGE_LEN);
+          struct MSCHAPv2_resp *resp = (struct MSCHAPv2_resp *)(ans + 1);
+
+          chap->challenge.peer[0] = sizeof resp->PeerChallenge;
+          memcpy(chap->challenge.peer + 1, resp->PeerChallenge,
+                 sizeof resp->PeerChallenge);
         }
 #endif
 
@@ -857,16 +854,21 @@ chap_Input(struct bundle *bundle, struct link *l, struct mbuf *bp)
           if (!radius_Authenticate(&bundle->radius, &chap->auth,
                                    chap->auth.in.name, ans, alen + 1,
                                    chap->challenge.local + 1,
-                                   *chap->challenge.local,
-                                   chap->challenge.peer + 1,
-                                   *chap->challenge.peer))
+                                   *chap->challenge.local))
             chap_Failure(&chap->auth);
         } else
 #endif
         {
+          if (p->link.lcp.want_authtype == 0x81 && ans[alen] != '\0' &&
+              alen == sizeof(struct MSCHAPv2_resp)) {
+            struct MSCHAPv2_resp *resp = (struct MSCHAPv2_resp *)(ans + 1);
+
+            log_Printf(LogWARN, "%s: Compensating for corrupt (Win98/WinME?) "
+                       "CHAP81 RESPONSE\n", l->name);
+            resp->Flags = '\0';	/* rfc2759 says it *MUST* be zero */
+          }
           key = auth_GetSecret(bundle, name, nlen, p);
           if (key) {
-            char *myans;
 #ifndef NODES
             if (p->link.lcp.want_authtype == 0x80 &&
                 lanman && !IsEnabled(p->link.lcp.cfg.chap80lm)) {
@@ -887,8 +889,8 @@ chap_Input(struct bundle *bundle, struct link *l, struct mbuf *bp)
             } else
 #endif
             {
-              myans = chap_BuildAnswer(name, key, chap->auth.id,
-                                       chap->challenge.local,
+              char *myans = chap_BuildAnswer(name, key, chap->auth.id,
+                                             chap->challenge.local,
                                        p->link.lcp.want_authtype
 #ifndef NODES
                                        , chap->challenge.peer,

usr.sbin/ppp/chap.h

@@ -63,6 +63,13 @@ struct chap {
 #define auth2chap(a) \
   ((struct chap *)((char *)a - (int)&((struct chap *)0)->auth))
 
+struct MSCHAPv2_resp {		/* rfc2759 */
+  char PeerChallenge[16];
+  char Reserved[8];
+  char NTResponse[24];
+  char Flags;
+};
+
 extern void chap_Init(struct chap *, struct physical *);
 extern void chap_ReInit(struct chap *);
 extern struct mbuf *chap_Input(struct bundle *, struct link *, struct mbuf *);

usr.sbin/ppp/pap.c

@@ -266,7 +266,7 @@ pap_Input(struct bundle *bundle, struct link *l, struct mbuf *bp)
 #ifndef NORADIUS
       if (*bundle->radius.cfg.file) {
         if (!radius_Authenticate(&bundle->radius, authp, authp->in.name,
-                                 key, strlen(key), NULL, 0, NULL, 0))
+                                 key, strlen(key), NULL, 0))
           pap_Failure(authp);
       } else
 #endif

usr.sbin/ppp/radius.c

@@ -700,7 +700,7 @@ radius_put_physical_details(struct rad_handle *rad, struct physical *p)
 int
 radius_Authenticate(struct radius *r, struct authinfo *authp, const char *name,
                     const char *key, int klen, const char *nchallenge,
-                    int nclen, const char *pchallenge, int pclen)
+                    int nclen)
 {
   struct timeval tv;
   int got;
@@ -712,6 +712,7 @@ radius_Authenticate(struct radius *r, struct authinfo *authp, const char *name,
 #ifndef NODES
   struct mschap_response msresp;
   struct mschap2_response msresp2;
+  const struct MSCHAPv2_resp *keyv2;
 #endif
 
   if (!*r->cfg.file)
@@ -794,26 +795,21 @@ radius_Authenticate(struct radius *r, struct authinfo *authp, const char *name,
       break;
 
     case 0x81:
-      if (klen != 50) {
+      if (klen != sizeof(*keyv2) + 1) {
         log_Printf(LogERROR, "CHAP81: Unrecognised key length %d\n", klen);
         rad_close(r->cx.rad);
         return 0;
       }
 
-      if (pclen != sizeof msresp2.pchallenge) {
-        log_Printf(LogERROR, "CHAP81: Unrecognised peer challenge length %d\n",
-                   pclen);
-        rad_close(r->cx.rad);
-        return 0;
-      }
-
+      keyv2 = (const struct MSCHAPv2_resp *)(key + 1);
       rad_put_vendor_attr(r->cx.rad, RAD_VENDOR_MICROSOFT,
                           RAD_MICROSOFT_MS_CHAP_CHALLENGE, nchallenge, nclen);
       msresp2.ident = *key;
-      msresp2.flags = 0x00;
-      memcpy(msresp2.response, key + 25, 24);
+      msresp2.flags = keyv2->Flags;
+      memcpy(msresp2.response, keyv2->NTResponse, sizeof msresp2.response);
       memset(msresp2.reserved, '\0', sizeof msresp2.reserved);
-      memcpy(msresp2.pchallenge, pchallenge, pclen);
+      memcpy(msresp2.pchallenge, keyv2->PeerChallenge,
+             sizeof msresp2.pchallenge);
       rad_put_vendor_attr(r->cx.rad, RAD_VENDOR_MICROSOFT,
                           RAD_MICROSOFT_MS_CHAP2_RESPONSE, &msresp2,
                           sizeof msresp2);

usr.sbin/ppp/radius.h

@@ -85,7 +85,7 @@ extern void radius_Destroy(struct radius *);
 extern void radius_Show(struct radius *, struct prompt *);
 extern int radius_Authenticate(struct radius *, struct authinfo *,
                                const char *, const char *, int,
-                               const char *, int, const char *, int);
+                               const char *, int);
 extern void radius_Account(struct radius *, struct radacct *,
                            struct datalink *, int, struct in_addr *,
                            struct in_addr *, struct pppThroughput *);