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Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>, Djalal Harouni <tixxdz@gmail.com>,
        Chris Mason <clm@fb.com>, tytso@mit.edu,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Josh Triplett <josh@joshtriplett.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
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        linux-security-module@vger.kernel.org,
        Dongsu Park <dongsu@endocode.com>,
        David Herrmann <dh.herrmann@googlemail.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Alban Crequy <alban.crequy@gmail.com>,
        Al Viro <viro@ZenIV.linux.org.uk>
Date: Tue, 17 May 2016 06:23:17 -0400
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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