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

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Message-ID: <f7fd4a35-3c04-4eb0-a58d-18ed8d7210b9@yandex.ru>
Date: Tue, 19 Nov 2024 14:03:16 +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,
 edumazet@...gle.com, gouhao@...ontech.com, horms@...nel.org,
 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 = {