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

[Kuniyuki Iwashima]

From: Heiko Carstens <hca@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxxx>

Thanks!
I'll post a formal patch.