Fix GSS-SPNEGO mechanism incompatible behavior

The GSS-SPNEGO mechanism has been designed and introduced by Microsoft for use
by Active Directory clients. It allows to negotiate an underlying
Security Mechanism like Krb5 or NTLMSSP.
However the implementaion in cyrus-sasl is broken and never correctly
interoperated with Microsoft servers or client. This patch fixes the
compatibility issue which is caused by incorrectly trying to negotiate
SSF layers explicitly instead of using the flags negotiated by GSSAPI
as required by the Microsoft implementation.

Signed-off-by: Simo Sorce <simo@redhat.com>

plugins/gssapi.c

@@ -620,10 +620,62 @@ static void gssapi_common_mech_free(void *global_context __attribute__((unused))
 #endif
 }
 
+/* The GSS-SPNEGO mechanism does not do SSF negotiation, instead it uses the
+ * flags negotiated by GSSAPI to determine If confidentiality or integrity are
+ * used. These flags are stored in text->qop transalated as layers by the
+ * caller */
+static int gssapi_spnego_ssf(context_t *text, const sasl_utils_t *utils,
+                             sasl_security_properties_t *props,
+                             sasl_out_params_t *oparams)
+{
+    OM_uint32 maj_stat = 0, min_stat = 0;
+    OM_uint32 max_input;
+
+    if (text->qop & LAYER_CONFIDENTIALITY) {
+        oparams->encode = &gssapi_privacy_encode;
+        oparams->decode = &gssapi_decode;
+        oparams->mech_ssf = K5_MAX_SSF;
+    } else if (text->qop & LAYER_INTEGRITY) {
+        oparams->encode = &gssapi_integrity_encode;
+        oparams->decode = &gssapi_decode;
+        oparams->mech_ssf = 1;
+    } else {
+        oparams->encode = NULL;
+        oparams->decode = NULL;
+        oparams->mech_ssf = 0;
+    }
+
+    if (oparams->mech_ssf) {
+        maj_stat = gss_wrap_size_limit(&min_stat,
+                                       text->gss_ctx,
+                                       1,
+                                       GSS_C_QOP_DEFAULT,
+                                       (OM_uint32)oparams->maxoutbuf,
+                                       &max_input);
+
+	if (max_input > oparams->maxoutbuf) {
+	    /* Heimdal appears to get this wrong */
+	    oparams->maxoutbuf -= (max_input - oparams->maxoutbuf);
+	} else {
+	    /* This code is actually correct */
+	    oparams->maxoutbuf = max_input;
+	}
+    }
+
+    text->state = SASL_GSSAPI_STATE_AUTHENTICATED;
+
+    /* used by layers */
+    _plug_decode_init(&text->decode_context, text->utils,
+		      (props->maxbufsize > 0xFFFFFF) ? 0xFFFFFF :
+                      props->maxbufsize);
+
+    return SASL_OK;
+}
+
 /*****************************  Server Section  *****************************/
 
 static int 
-gssapi_server_mech_new(void *glob_context __attribute__((unused)), 
+gssapi_server_mech_new(void *glob_context,
 		       sasl_server_params_t *params,
 		       const char *challenge __attribute__((unused)), 
 		       unsigned challen __attribute__((unused)),
@@ -645,6 +697,7 @@ gssapi_server_mech_new(void *glob_context __attribute__((unused)),
     text->state = SASL_GSSAPI_STATE_AUTHNEG;
 
     text->http_mode = (params->flags & SASL_NEED_HTTP);
+    text->mech_type = (gss_OID) glob_context;
 
     *conn_context = text;
 
@@ -658,7 +711,7 @@ gssapi_server_mech_authneg(context_t *text,
 			   unsigned clientinlen,
 			   const char **serverout,
 			   unsigned *serveroutlen,
-			   sasl_out_params_t *oparams __attribute__((unused)))
+			   sasl_out_params_t *oparams)
 {
     gss_buffer_t input_token, output_token;
     gss_buffer_desc real_input_token, real_output_token;
@@ -937,8 +990,9 @@ gssapi_server_mech_authneg(context_t *text,
 	/* HTTP doesn't do any ssf negotiation */
 	text->state = SASL_GSSAPI_STATE_AUTHENTICATED;
 	ret = SASL_OK;
-    }
-    else {
+    } else if (text->mech_type && text->mech_type == &gss_spnego_oid) {
+        ret = gssapi_spnego_ssf(text, params->utils, &params->props, oparams);
+    } else {
 	/* Switch to ssf negotiation */
 	text->state = SASL_GSSAPI_STATE_SSFCAP;
 	ret = SASL_CONTINUE;
@@ -1352,7 +1406,7 @@ static sasl_server_plug_t gssapi_server_plugins[] =
 	| SASL_FEAT_ALLOWS_PROXY
 	| SASL_FEAT_DONTUSE_USERPASSWD
 	| SASL_FEAT_SUPPORTS_HTTP,	/* features */
-	NULL,				/* glob_context */
+	&gss_spnego_oid,		/* glob_context */
 	&gssapi_server_mech_new,	/* mech_new */
 	&gssapi_server_mech_step,	/* mech_step */
 	&gssapi_common_mech_dispose,	/* mech_dispose */
@@ -1730,7 +1784,11 @@ static int gssapi_client_mech_step(void *conn_context,
 		text->state = SASL_GSSAPI_STATE_AUTHENTICATED;
 		oparams->doneflag = 1;
 		return SASL_OK;
-	    }
+	    } else if (text->mech_type && text->mech_type == &gss_spnego_oid) {
+		oparams->doneflag = 1;
+                return gssapi_spnego_ssf(text, params->utils, &params->props,
+                                         oparams);
+            }
 
 	    /* Switch to ssf negotiation */
 	    text->state = SASL_GSSAPI_STATE_SSFCAP;