linux-kernel - Re: [PATCH v2] net/unix: pass pidfd flags via SCM

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Message-ID: <67638eaf-3d94-450a-8280-df4f7dc66ce7@yandex.ru>
Date: Tue, 19 Nov 2024 14:04:41 +0300
From: stsp <stsp2@...dex.ru>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: almasrymina@...gle.com, asml.silence@...il.com, axboe@...nel.dk,
 brauner@...nel.org, cyphar@...har.com, davem@...emloft.net,
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 kees@...nel.org, krisman@...e.de, kuba@...nel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, mhal@...x.co,
 netdev@...r.kernel.org, oleg@...hat.com, pabeni@...hat.com,
 quic_abchauha@...cinc.com, shuah@...nel.org, tandersen@...flix.com,
 viro@...iv.linux.org.uk, willemb@...gle.com
Subject: Re: [PATCH v2] net/unix: pass pidfd flags via SCM_PIDFD cmsg

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 = {