path-util: introduce path_is_safe()

The function is similar to path_is_valid(), but it refuses paths which
contain ".." component.

src/basic/path-util.c

@@ -1037,14 +1037,14 @@ bool filename_is_valid(const char *p) {
         return true;
 }
 
-bool path_is_valid(const char *p) {
+bool path_is_valid_full(const char *p, bool accept_dot_dot) {
         if (isempty(p))
                 return false;
 
         for (const char *e = p;;) {
                 int r;
 
-                r = path_find_first_component(&e, /* accept_dot_dot= */ true, NULL);
+                r = path_find_first_component(&e, accept_dot_dot, NULL);
                 if (r < 0)
                         return false;
 

src/basic/path-util.h

@@ -155,7 +155,13 @@ int path_extract_filename(const char *p, char **ret);
 int path_extract_directory(const char *p, char **ret);
 
 bool filename_is_valid(const char *p) _pure_;
-bool path_is_valid(const char *p) _pure_;
+bool path_is_valid_full(const char *p, bool accept_dot_dot) _pure_;
+static inline bool path_is_valid(const char *p) {
+        return path_is_valid_full(p, true);
+}
+static inline bool path_is_safe(const char *p) {
+        return path_is_valid_full(p, false);
+}
 bool path_is_normalized(const char *p) _pure_;
 
 char *file_in_same_dir(const char *path, const char *filename);