linux-kernel - Re: [PATCH net-next v7 1/4] scm: add SO_PASSPIDFD and SCM

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Message-ID: <20230901205613.59455-1-kuniyu@amazon.com>
Date:   Fri, 1 Sep 2023 13:56:13 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <hca@...ux.ibm.com>
CC:     <aleksandr.mikhalitsyn@...onical.com>, <arnd@...db.de>,
        <bluca@...ian.org>, <brauner@...nel.org>, <davem@...emloft.net>,
        <dsahern@...nel.org>, <edumazet@...gle.com>,
        <keescook@...omium.org>, <kuba@...nel.org>, <kuniyu@...zon.com>,
        <ldv@...ace.io>, <leon@...nel.org>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <mzxreary@...inter.de>,
        <netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH net-next v7 1/4] scm: add SO_PASSPIDFD and SCM_PIDFD

From: Heiko Carstens <hca@...ux.ibm.com>
Date: Fri, 1 Sep 2023 22:51:45 +0200
> On Fri, Sep 01, 2023 at 01:33:22PM -0700, Kuniyuki Iwashima wrote:
> > From: Heiko Carstens <hca@...ux.ibm.com>
> > Date: Fri, 1 Sep 2023 22:05:17 +0200
> > > On Thu, Jun 08, 2023 at 10:26:25PM +0200, Alexander Mikhalitsyn wrote:
> > > > +	if ((msg->msg_controllen <= sizeof(struct cmsghdr)) ||
> > > > +	    (msg->msg_controllen - sizeof(struct cmsghdr)) < sizeof(int)) {
> > > > +		msg->msg_flags |= MSG_CTRUNC;
> > > > +		return;
> > > > +	}
> > > 
> > > This does not work for compat tasks since the size of struct cmsghdr (aka
> > > struct compat_cmsghdr) is differently. If the check from put_cmsg() is
> > > open-coded here, then also a different check for compat tasks needs to be
> > > added.
> > > 
> > > Discovered this because I was wondering why strace compat tests fail; it
> > > seems because of this.
> > > 
> > > See https://github.com/strace/strace/blob/master/tests/scm_pidfd.c
> > > 
> > > For compat tasks recvmsg() returns with msg_flags=MSG_CTRUNC since the
> > > above code expects a larger buffer than is necessary.
> > 
> > Can you test this ?
> 
> Works for me.
> 
> Tested-by: Heiko Carstens <hca@...ux.ibm.com>

Thanks!
I'll post a formal patch.