linux-kernel - Re: pselect/etc semantics

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Message-ID: <CAK8P3a3BkgrT2vvX8NhZ8y1G_1tyefb8LPSk+EZKBrHqPuXoqQ@mail.gmail.com>
Date:   Thu, 30 May 2019 20:28:24 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, dbueso@...e.de,
        Jens Axboe <axboe@...nel.dk>,
        Davidlohr Bueso <dave@...olabs.net>, e@...24.org,
        Jason Baron <jbaron@...mai.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>, omar.kilani@...il.com,
        Thomas Gleixner <tglx@...utronix.de>,
        "# 3.4.x" <stable@...r.kernel.org>
Subject: Re: pselect/etc semantics

On Thu, May 30, 2019 at 3:54 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Arnd Bergmann <arnd@...db.de> writes:
> > On Wed, May 29, 2019 at 6:12 PM Oleg Nesterov <oleg@...hat.com> wrote:

> >
> > Not sure about the order of the cleanups, but probably something like
> > this would work:
> >
> > 1. fix the race (to be backported)
> > 2. unify set_compat_user_sigmask/set_user_sigmask
> > 3. remove unneeded compat handlers
> > 4. replace restore_user_sigmask with restore_saved_sigmask_if()
> > 5. also unify compat_get_fd_set()/get_fd_set() and kill off
> >     compat select() variants.
>
> Are new system calls added preventing a revert of the patch in question
> for stable kernels?

Yes, a straight revert would not work, as it was done as a cleanup in
order to simplify the following conversion. I suppose one could undo
the cleanup in both the time32 and time64 versions of each syscall,
but I would consider that a more risky change than just fixing the
bug that was reported.

       Arnd