linux-kernel - Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

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Message-ID: <1463480597.2509.0.camel@HansenPartnership.com>
Date:	Tue, 17 May 2016 06:23:17 -0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Serge Hallyn <serge.hallyn@...ntu.com>,
	Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
	tytso@....edu, Serge Hallyn <serge.hallyn@...onical.com>,
	Josh Triplett <josh@...htriplett.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andy Lutomirski <luto@...nel.org>,
	Seth Forshee <seth.forshee@...onical.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Dongsu Park <dongsu@...ocode.com>,
	David Herrmann <dh.herrmann@...glemail.com>,
	Miklos Szeredi <mszeredi@...hat.com>,
	Alban Crequy <alban.crequy@...il.com>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

On Mon, 2016-05-16 at 22:47 -0500, Serge E. Hallyn wrote:
> On Mon, May 16, 2016 at 10:28:32PM -0400, James Bottomley wrote:
> > On Mon, 2016-05-16 at 19:41 +0000, Serge Hallyn wrote:
> > > Hey James,
> > > 
> > > I probably did something wrong - but i applied your patch onto
> > > 4.6,
> > > compiled in shiftfs, did
> > > 
> > > mount -t shiftfs -o uidmap=0:100000:65536,gidmap=0:100000:65536
> > > /home/ubuntu /mnt
> > > 
> > > and ls segfaults and gives me kernel syslog msgs like:
> > 
> > Hm, it looks to be something IMA related, since the SUSE default is
> > no
> > IMA and this BUG in the filesystem is to do with the IMA version of
> > i_readcount_dec.  I'll recompile my kernel to see if I can
> > reproduce. 
> >  Just in case, what's the underlying filesystem on /home/ubuntu?
> 
> It was ext4

Thanks.  I've got it to reproduce with CONFIG_IMA set ... just
debugging now.

James