linux-kernel - Re: [PATCH 1/4] exec: Change uselib(2) IS

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Message-ID: <20200519081134.voejjt77b3qjf22h@wittgenstein>
Date:   Tue, 19 May 2020 10:11:34 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Jann Horn <jannh@...gle.com>, Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Eric Biggers <ebiggers3@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] exec: Change uselib(2) IS_SREG() failure to EACCES

On Mon, May 18, 2020 at 06:57:15PM -0500, Eric W. Biederman wrote:
> Christian Brauner <christian.brauner@...ntu.com> writes:
> 
> > On Mon, May 18, 2020 at 04:43:20PM +0200, Jann Horn wrote:
> >> On Mon, May 18, 2020 at 3:03 PM Christian Brauner
> >> <christian.brauner@...ntu.com> wrote:
> >> > Also - gulp (puts on flame proof suit) - may I suggest we check if there
> >> > are any distros out there that still set CONFIG_USELIB=y
> >> 
> >> Debian seems to have it enabled on x86...
> >> 
> >> https://salsa.debian.org/kernel-team/linux/-/blob/master/debian/config/kernelarch-x86/config#L1896
> >> 
> >> A random Ubuntu 19.10 VM I have here has it enabled, too.
> >
> > I wonder if there's any program - apart from _ancient_ glibc out there
> > that actually use it...
> > I looked at uselib in codsearch but the results were quite unspecific
> > but I didn't look too close.
> 
> So the thing to do is to have a polite word with people who build Ubuntu
> and Debian kernels and get them to disable the kernel .config.

Yeah, I think that's a sane thing to do.
I filed a bug for Ubuntu to start a discussion. I can't see an obvious
reason why not.

> 
> A quick look suggets it is already disabled in RHEL8.  It cannot be
> disabled in RHEL7.
> 
> Then in a few years we can come back and discuss removing the uselib
> system call, base on no distributions having it enabled.
> 
> If it was only libc4 and libc5 that used the uselib system call then it
> can probably be removed after enough time.
> 
> We can probably reorganize the code before the point it is clearly safe
> to drop support for USELIB to keep it off to the side so USELIB does not
> have any ongoing mainteance costs.
> 
> For this patchset I think we need to assume uselib will need to be
> maintained for a bit longer.

Yeah, agreed. It doesn't matter as long as we have a plan for the future
to remove it. I don't think keeping this cruft around forever should be
the only outlook.

Christian