linux-kernel - Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1

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Message-ID: <CAG48ez0yLF4KAK5uMi1_b9woC7NYy0NamYD1jP7BOPJkpKR7Mw@mail.gmail.com>
Date:   Thu, 30 Apr 2020 05:41:07 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Bernd Edlinger <bernd.edlinger@...mail.de>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [GIT PULL] Please pull proc and exec work for 5.7-rc1

On Thu, Apr 30, 2020 at 5:26 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Apr 29, 2020 at 8:00 PM Jann Horn <jannh@...gle.com> wrote:
> >
> > But if we go with Bernd's approach together with your restart
> > suggestion,
>
> So repeat after me: Bernd's approach _without_ the restart is unacceptable.
>
> It's unacceptable because it breaks things that currently work, and
> returns EAGAIN in situations where that is simple not a valid error
> code.

Sure, makes sense to me. I'm not eager to start randomly throwing
EAGAIN where it couldn't happen before either (and I initially missed
that Bernd's patch did that for procfs files, too).

> That bug has nothing to do with ptrace(). It's literally a "write()"
> to a file in /proc.
>
> What is so hard to get about this basic thing?

You said:

| So a ptrace() user (or [...] wouldn't even see the impossible EAGAIN error.

So I assumed you explicitly wanted ptrace() to restart, too. I was
just pointing out that that didn't make sense to me.