linux-kernel - Re: [PATCH 3/6] exec: Stop open coding mutex_lock_killable of cred_guard

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Message-ID: <CAHk-=wguq6FwYb8_WZ_ZOxpHtwyc0xpz+PitNuf4pVxjWFmjFQ@mail.gmail.com>
Date:   Sat, 9 May 2020 12:18:06 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Rob Landley <rob@...dley.net>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/6] exec: Stop open coding mutex_lock_killable of cred_guard_mutex

On Fri, May 8, 2020 at 11:48 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
>
> Oleg modified the code that did
> "mutex_lock_interruptible(&current->cred_guard_mutex)" to return
> -ERESTARTNOINTR instead of -EINTR, so that userspace will never see a
> failure to grab the mutex.
>
> Slightly earlier Liam R. Howlett defined mutex_lock_killable for
> exactly the same situation but it does it a little more cleanly.

What what what?

None of this makes sense. Your commit message is completely wrong, and
the patch is utter shite.

mutex_lock_interruptible() and mutex_lock_killable() are completely
different operations, and the difference has absolutely nothing to do
with  -ERESTARTNOINTR or -EINTR.

mutex_lock_interruptible() is interrupted by any signal.

mutex_lock_killable() is - surprise surprise - only interrupted by
SIGKILL (in theory any fatal signal, but we never actually implemented
that logic, so it's only interruptible by the known-to-always-be-fatal
SIGKILL).

> Switch the code to mutex_lock_killable so that it is clearer what the
> code is doing.

This nonsensical patch makes me worry about all your other patches.
The explanation is wrong, the patch is wrong, and it changes things to
be fundamentally broken.

Before this, ^C would break out of a blocked execve()/ptrace()
situation. After this patch, you need special tools to do so.

This patch is completely wrong.

And Kees, what the heck is that "Reviewed-by" for? Worthless review too.

                Linus