Re: [PATCH v2] net/unix: pass pidfd flags via SCM_PIDFD cmsg

[stsp <stsp2@yandex.ru>]

16.11.2024 04:10, Kuniyuki Iwashima пишет:
> Now this allows sending pidfd without SO_PASSPIDFD, so you need to
> add a validation for "if (!msg->msg_control)" in __scm_recv_common().
Will do, thanks.
Btw don't we need MSG_CTRUNC in
such case even if "msg_control"exists?
Or the established practice is to just drop cmsg silently?
I mean, something like the below:

--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -176,12 +176,19 @@ static inline bool __scm_recv_common(struct socket 
*sock, struct msghdr *msg,
         if (!msg->msg_control) {
                 if (test_bit(SOCK_PASSCRED, &sock->flags) ||
                     test_bit(SOCK_PASSPIDFD, &sock->flags) ||
-                   scm->fp || scm_has_secdata(sock))
+                   scm->fp || scm_has_secdata(sock) ||
+                   scm->pidfd_flags)
                         msg->msg_flags |= MSG_CTRUNC;
                 scm_destroy(scm);
                 return false;
         }

+       if (!test_bit(SOCK_PASSPIDFD, &sock->flags) && scm->pidfd_flags) {
+               msg->msg_flags |= MSG_CTRUNC;
+               scm_destroy(scm);
+               return false;
+       }
+
         if (test_bit(SOCK_PASSCRED, &sock->flags)) {
                 struct user_namespace *current_ns = current_user_ns();
                 struct ucred ucreds = {