Fix SPNEGO context import

The patches for CVE-2015-2695 did not implement a SPNEGO
gss_import_sec_context() function, under the erroneous belief that an
exported SPNEGO context would be tagged with the underlying context
mechanism.  Implement it now to allow SPNEGO contexts to be
successfully exported and imported after establishment.

(cherry picked from commit 222b09f)
(cherry picked from commit 8e10a78)

ticket: 8284
version_fixed: 1.13.3
status: resolved

src/lib/gssapi/spnego/spnego_mech.c

@@ -2253,12 +2253,33 @@ spnego_gss_import_sec_context(
 	const gss_buffer_t	interprocess_token,
 	gss_ctx_id_t		*context_handle)
 {
-	/*
-	 * Until we implement partial context exports, there are no SPNEGO
-	 * exported context tokens, only tokens for underlying mechs.  So just
-	 * return an error for now.
-	 */
-	return GSS_S_UNAVAILABLE;
+	OM_uint32 ret, tmpmin;
+	gss_ctx_id_t mctx;
+	spnego_gss_ctx_id_t sc;
+	int initiate, opened;
+
+	ret = gss_import_sec_context(minor_status, interprocess_token, &mctx);
+	if (ret != GSS_S_COMPLETE)
+		return ret;
+
+	ret = gss_inquire_context(&tmpmin, mctx, NULL, NULL, NULL, NULL, NULL,
+				  &initiate, &opened);
+	if (ret != GSS_S_COMPLETE || !opened) {
+		/* We don't currently support importing partially established
+		 * contexts. */
+		(void) gss_delete_sec_context(&tmpmin, &mctx, GSS_C_NO_BUFFER);
+		return GSS_S_FAILURE;
+	}
+
+	sc = create_spnego_ctx(initiate);
+	if (sc == NULL) {
+		(void) gss_delete_sec_context(&tmpmin, &mctx, GSS_C_NO_BUFFER);
+		return GSS_S_FAILURE;
+	}
+	sc->ctx_handle = mctx;
+	sc->opened = 1;
+	*context_handle = (gss_ctx_id_t)sc;
+	return GSS_S_COMPLETE;
 }
 #endif /* LEAN_CLIENT */