linux-kernel - Re: [PATCH RFC 0/1] mount: universally disallow mounting over symlinks

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Date:   Mon, 13 Jan 2020 14:03:00 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Aleksa Sarai <cyphar@...har.com>,
        David Howells <dhowells@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        stable@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Serge Hallyn <serge@...lyn.com>, dev@...ncontainers.org,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/1] mount: universally disallow mounting over
 symlinks

On Mon, 2020-01-13 at 14:00 +0800, Ian Kent wrote:
> On Mon, 2020-01-13 at 03:54 +0000, Al Viro wrote:
> > On Mon, Jan 13, 2020 at 09:48:23AM +0800, Ian Kent wrote:
> > 
> > > I did try this patch and I was trying to work out why it didn't
> > > work. But thought I'd let you know what I saw.
> > > 
> > > Applying it to current Linus tree systemd stops at switch root.
> > > 
> > > Not sure what causes that, I couldn't see any reason for it.
> > 
> > Wait a minute...  So you are seeing problems early in the boot,
> > before any autofs ioctls might come into play?
> 
> I did, then I checked it booted without the patch, then tried
> building from scratch with the patch twice and same thing
> happened each time.
> 
> Looked like this, such as it is:
> [ OK ] Reached target Switch Root.
> [ OK ] Started Plymouth switch root service.
>        Starting Switch Root...
> 
> I don't have any evidence but thought it might be this:
> https://github.com/karelzak/util-linux/blob/master/sys-utils/switch_root.c

Oh wait, for systemd I was actually looking at:
https://github.com/systemd/systemd/blob/master/src/shared/switch-root.c

> 
> Mind you, that's not the actual systemd repo. either I probably
> need to look a lot deeper (and at the actual systemd repo) to
> work out what's actually being called.
> 
> > Sigh...  Guess I'll have to dig that Fedora KVM image out and
> > try to see what it's about... ;-/  Here comes a couple of hours
> > of build...