linux-kernel - Re: [PATCH v2] signal: add procfd

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Date:   Thu, 29 Nov 2018 22:40:49 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     christian@...uner.io
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>, cyphar@...har.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        Tim Murray <timmurray@...gle.com>, linux-man@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] signal: add procfd_signal() syscall

On Thu, Nov 29, 2018 at 10:35 PM Christian Brauner <christian@...uner.io> wrote:
> On Thu, Nov 29, 2018 at 10:02:13PM +0100, Arnd Bergmann wrote:
> > On Thu, Nov 29, 2018 at 9:14 PM Andy Lutomirski <luto@...capital.net> wrote:
> >
> > Is the current procfd_signal() proposal (under whichever name) sufficient
> > to correctly implement both sys_rt_sigqueueinfo() and sys_rt_tgsigqueueinfo()?
>
> Yes, I see no reason why not. My idea is to extend it - after we have a
> basic version in - to also work with:
> /proc/<pid>/task/<tid>
> If I'm not mistaken this should be sufficient to get rt_tgsigqueueinfo.
> The thread will be uniquely identified by the tid descriptor and no
> combination of /proc/<pid> and /proc/<pid>/task/<tid> is needed. Does
> that sound reasonable?

Yes. So it would currently replace rt_gsigqueueinfo() but
not rt_tgsigqueueinfo(), and could be extended to do both
afterwards, without making the interface ugly in any form?

I suppose we can always add more flags if needed, and you
already ensure that flags is zero for the moment.

> > Can we implement sys_rt_sigtimedwait() based on signalfd()?
> >
> > If yes, that would leave waitid(), which already needs a replacement
> > for y2038, and that should then also return a signalfd_siginfo.
> > My current preference for waitid() would be to do a version that
> > closely resembles the current interface, but takes a signalfd_siginfo
> > and a __kernel_timespec based rusage replacement (possibly
> > two of them to let us map wait6), but does not operate on procfd or
> > take a signal mask. That would require yet another syscall, but I
> > don't think I can do that before we want to have the set of y2038
> > safe syscalls.
>
> All sounds reasonable to me but that's not a blocker for the current
> syscall though, is it?

I'd like to at least understand about sys_rt_sigtimedwait() before
we go on, so we all know what's coming, and document the
plans in the changelog.

waitid() probably remains on my plate anyway, and I hope understand
where we're at with it.

     Arnd