fix(pkg/rootless): avoid memleak during init() contructor.

`argv[0]`, ie: the full buffer allocated by `get_cmd_line_args`,
was going to be freed only if `can_use_shortcut()` was called.
Since that is not always the case, add a fallback cleanup method.

Signed-off-by: Federico Di Pierro <[email protected]>

pkg/rootless/rootless_linux.c

@@ -439,6 +439,7 @@ static void __attribute__((constructor)) init()
   const char *listen_fds;
   const char *listen_fdnames;
   cleanup_free char **argv = NULL;
+  cleanup_free char *argv0 = NULL;
   cleanup_dir DIR *d = NULL;
   int argc;
 
@@ -496,6 +497,8 @@ static void __attribute__((constructor)) init()
       fprintf(stderr, "cannot retrieve cmd line");
       _exit (EXIT_FAILURE);
     }
+  // Even if unused, this is needed to ensure we properly free the memory
+  argv0 = argv[0];
 
   if (geteuid () != 0 || getenv ("_CONTAINERS_USERNS_CONFIGURED") == NULL)
     do_preexec_hooks(argv, argc);
@@ -525,6 +528,8 @@ static void __attribute__((constructor)) init()
   xdg_runtime_dir = getenv ("XDG_RUNTIME_DIR");
   if (geteuid () != 0 && xdg_runtime_dir && xdg_runtime_dir[0] && can_use_shortcut (argv))
     {
+      // It was freed by can_use_shortcut() call
+      argv0 = NULL;
       cleanup_free char *cwd = NULL;
       cleanup_close int userns_fd = -1;
       cleanup_close int mntns_fd = -1;