+/*
+ * The 'gssapi_keyex' userauth mechanism.
+ */
+static int
+userauth_gsskeyex(Authctxt *authctxt)
+{
+ int authenticated = 0;
+ Buffer b, b2;
+ gss_buffer_desc mic, gssbuf, gssbuf2;
+ u_int len;
+
+ mic.value = packet_get_string(&len);
+ mic.length = len;
+
+ packet_check_eom();
+
+ ssh_gssapi_buildmic(&b, authctxt->user, authctxt->service,
+ "gssapi-keyex");
+
+ gssbuf.value = buffer_ptr(&b);
+ gssbuf.length = buffer_len(&b);
+
+ /* client may have used empty username to determine target
+ name from GSSAPI context */
+ ssh_gssapi_buildmic(&b2, "", authctxt->service, "gssapi-keyex");
+
+ gssbuf2.value = buffer_ptr(&b2);
+ gssbuf2.length = buffer_len(&b2);
+
+ /* gss_kex_context is NULL with privsep, so we can't check it here */
+ if (!GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gss_kex_context,
+ &gssbuf, &mic))) ||
+ !GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gss_kex_context,
+ &gssbuf2, &mic)))) {
+ if (authctxt->valid && authctxt->user && authctxt->user[0]) {
+ authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user,
+ authctxt->pw,
+ 1 /* gssapi-keyex */));
+ }
+ }
+
+ buffer_free(&b);
+ buffer_free(&b2);
+ xfree(mic.value);
+
+ return (authenticated);
+}
+