linux-kernel - Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on userns mounts, breaking systemd-nspawn

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Date:   Sat, 22 Dec 2018 14:20:16 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     nix.or.die@...il.com, "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     ellierevves@...il.com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>, seth.forshee@...onical.com
Subject: Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on
 userns mounts, breaking systemd-nspawn

Eric, this is entirely unacceptable.

On Sat, Dec 22, 2018 at 12:58 PM Gabriel C <nix.or.die@...il.com> wrote:
>
> Added some people to CC that might want to see this..

Thanks.

> > Here's an email that was sent to lkml about the subject:
> >
> > https://lkml.org/lkml/2018/7/5/742
> >
> > I link also this, quoting the last of it:
> >
> > https://lkml.org/lkml/2018/7/5/701
> >
> > It has never been the case that mknod on a device node will guarantee
> > that you even can open the device node.  The applications that regress
> > are broken.  It doesn't mean we shouldn't be bug compatible, but we darn
> > well should document very clearly the bugs we are being bug compatible with.

Yeah, this is complete garbage.

We have very clear rules in the kernel: if some change breaks existing
setups, it is ABSOLUTELY NEVER the application that is broken.

It is the kernel.

There is absolutely zero gray areas here. Eric, your behavior is
entirely out of line, and now we apparently have a regression that
goes back to June that I was not told about because of your incorrect
stance.

Eric, I want to make this 1000% clear: there are no user space bugs.
If it used to work, then user space was clearly doing the right thing.
The fact that you tried to several times claim it was buggy user space
is a serious breach of trust. You KNOW this is the case.

Seriously. There are no excuses.

That commit is now reverted in my tree, and furthermore I will not
take any pull requests from you until you have made it clear that you
comprehend this very fundamental issue.

Why did it take so long for this issue to be elevated to me?

                   Linus