From 0f0502109eac44128e87906fff30b5d049392f1d Mon Sep 17 00:00:00 2001 From: ShadowNinja Date: Fri, 16 Dec 2016 17:43:39 -0500 Subject: [PATCH] Security: Fix resolving of some relative paths Trying to resolve a path with RemoveRelativePathComponents that can't be resolved without leaving leading parent components (e.g. "../worlds/foo" or "bar/../../worlds/foo") will fail. To work around this, we leave the relative components and simply remove the trailing components one at a time, and bail out when we find a parent component. This will still fail for paths like "worlds/foo/noexist/../auth.txt" (the path before the last parent component must not exist), but this is fine since you won't be able to open a file with a path like that anyways (the O.S. will determine that the path doesn't exist. Try `cat /a/../etc/passwd`). --- src/script/cpp_api/s_security.cpp | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-) diff --git a/src/script/cpp_api/s_security.cpp b/src/script/cpp_api/s_security.cpp index b915747c6..1b1f148cd 100644 --- a/src/script/cpp_api/s_security.cpp +++ b/src/script/cpp_api/s_security.cpp @@ -344,8 +344,7 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path, std::string str; // Transient - std::string norel_path = fs::RemoveRelativePathComponents(path); - std::string abs_path = fs::AbsolutePath(norel_path); + std::string abs_path = fs::AbsolutePath(path); if (!abs_path.empty()) { // Don't allow accessing the settings file @@ -356,18 +355,29 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path, // If we couldn't find the absolute path (path doesn't exist) then // try removing the last components until it works (to allow // non-existent files/folders for mkdir). - std::string cur_path = norel_path; + std::string cur_path = path; std::string removed; while (abs_path.empty() && !cur_path.empty()) { - std::string tmp_rmed; - cur_path = fs::RemoveLastPathComponent(cur_path, &tmp_rmed); - removed = tmp_rmed + (removed.empty() ? "" : DIR_DELIM + removed); + std::string component; + cur_path = fs::RemoveLastPathComponent(cur_path, &component); + if (component == "..") { + // Parent components can't be allowed or we could allow something like + // /home/user/minetest/worlds/foo/noexist/../../../../../../etc/passwd. + // If we have previous non-relative elements in the path we might be + // able to remove them so that things like worlds/foo/noexist/../auth.txt + // could be allowed, but those paths will be interpreted as nonexistent + // by the operating system anyways. + return false; + } + removed = component + (removed.empty() ? "" : DIR_DELIM + removed); abs_path = fs::AbsolutePath(cur_path); } - if (abs_path.empty()) return false; + if (abs_path.empty()) + return false; // Add the removed parts back so that you can't, eg, create a // directory in worldmods if worldmods doesn't exist. - if (!removed.empty()) abs_path += DIR_DELIM + removed; + if (!removed.empty()) + abs_path += DIR_DELIM + removed; // Get server from registry lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_SCRIPTAPI);