From 0486590c2944b39b480ab1713026ea402420863e Mon Sep 17 00:00:00 2001
From: Jakub Hrozek <jhrozek@redhat.com>
Date: Mon, 16 Mar 2020 21:09:37 +0100
Subject: [PATCH 4/6] Backport of improve validation of the post-logout URL;
 closes #449

---
 src/mod_auth_openidc.c | 90 +++++++++++++++++++++++++-----------------
 1 file changed, 53 insertions(+), 37 deletions(-)

diff --git a/src/mod_auth_openidc.c b/src/mod_auth_openidc.c
index b504ecbf62f839a82ad205fa5f825f9a8428dfdb..431e89e086fbb72f56ea2a212e63c6ac693f62a2 100644
--- a/src/mod_auth_openidc.c
+++ b/src/mod_auth_openidc.c
@@ -2083,6 +2083,52 @@ static int oidc_handle_logout_request(request_rec *r, oidc_cfg *c,
 	return HTTP_MOVED_TEMPORARILY;
 }
 
+static apr_byte_t oidc_validate_post_logout_url(request_rec *r, const char *url, char **err_str, char **err_desc) {
+       apr_uri_t uri;
+       const char *c_host = NULL;
+
+       if (apr_uri_parse(r->pool, url, &uri) != APR_SUCCESS) {
+               *err_str = apr_pstrdup(r->pool, "Malformed URL");
+               *err_desc = apr_psprintf(r->pool, "Logout URL malformed: %s", url);
+               oidc_error(r, "%s: %s", *err_str, *err_desc);
+               return FALSE;
+       }
+
+       c_host = oidc_get_current_url_host(r);
+       if ((uri.hostname != NULL)
+                       && ((strstr(c_host, uri.hostname) == NULL)
+                                       || (strstr(uri.hostname, c_host) == NULL))) {
+               *err_str = apr_pstrdup(r->pool, "Invalid Request");
+               *err_desc =
+                               apr_psprintf(r->pool,
+                                               "logout value \"%s\" does not match the hostname of the current request \"%s\"",
+                                               apr_uri_unparse(r->pool, &uri, 0), c_host);
+               oidc_error(r, "%s: %s", *err_str, *err_desc);
+               return FALSE;
+       } else if (strstr(url, "/") != url) {
+               *err_str = apr_pstrdup(r->pool, "Malformed URL");
+               *err_desc =
+                               apr_psprintf(r->pool,
+                                               "No hostname was parsed and it does not seem to be relative, i.e starting with '/': %s",
+                                               url);
+               oidc_error(r, "%s: %s", *err_str, *err_desc);
+               return FALSE;
+       }
+
+       /* validate the URL to prevent HTTP header splitting */
+       if (((strstr(url, "\n") != NULL) || strstr(url, "\r") != NULL)) {
+               *err_str = apr_pstrdup(r->pool, "Invalid Request");
+               *err_desc =
+                               apr_psprintf(r->pool,
+                                               "logout value \"%s\" contains illegal \"\n\" or \"\r\" character(s)",
+                                               url);
+               oidc_error(r, "%s: %s", *err_str, *err_desc);
+               return FALSE;
+       }
+
+       return TRUE;
+}
+
 /*
  * perform (single) logout
  */
@@ -2090,6 +2136,8 @@ static int oidc_handle_logout(request_rec *r, oidc_cfg *c, session_rec *session)
 
 	/* pickup the command or URL where the user wants to go after logout */
 	char *url = NULL;
+	char *error_str = NULL;
+	char *error_description = NULL;
 	oidc_util_get_request_parameter(r, "logout", &url);
 
 	oidc_debug(r, "enter (url=%s)", url);
@@ -2103,44 +2151,12 @@ static int oidc_handle_logout(request_rec *r, oidc_cfg *c, session_rec *session)
 		url = c->default_slo_url;
 
 	} else {
-
 		/* do input validation on the logout parameter value */
-
-		const char *error_description = NULL;
-		apr_uri_t uri;
-
-		if (apr_uri_parse(r->pool, url, &uri) != APR_SUCCESS) {
-			const char *error_description = apr_psprintf(r->pool,
-					"Logout URL malformed: %s", url);
-			oidc_error(r, "%s", error_description);
-			return oidc_util_html_send_error(r, c->error_template,
-					"Malformed URL", error_description,
-					HTTP_INTERNAL_SERVER_ERROR);
-
-		}
-
-		if ((strstr(r->hostname, uri.hostname) == NULL)
-				|| (strstr(uri.hostname, r->hostname) == NULL)) {
-			error_description =
-					apr_psprintf(r->pool,
-							"logout value \"%s\" does not match the hostname of the current request \"%s\"",
-							apr_uri_unparse(r->pool, &uri, 0), r->hostname);
-			oidc_error(r, "%s", error_description);
-			return oidc_util_html_send_error(r, c->error_template,
-					"Invalid Request", error_description,
-					HTTP_INTERNAL_SERVER_ERROR);
-		}
-
-		/* validate the URL to prevent HTTP header splitting */
-		if (((strstr(url, "\n") != NULL) || strstr(url, "\r") != NULL)) {
-			error_description =
-					apr_psprintf(r->pool,
-							"logout value \"%s\" contains illegal \"\n\" or \"\r\" character(s)",
-							url);
-			oidc_error(r, "%s", error_description);
-			return oidc_util_html_send_error(r, c->error_template,
-					"Invalid Request", error_description,
-					HTTP_INTERNAL_SERVER_ERROR);
+		if (oidc_validate_post_logout_url(r, url, &error_str,
+			&error_description) == FALSE) {
+		return oidc_util_html_send_error(r, c->error_template, error_str,
+			error_description,
+			HTTP_BAD_REQUEST); 
 		}
 	}
 
-- 
2.21.1