linux-kernel - Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in s_user

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Message-ID: <20151205061558.GA14580@ubuntu-hedt>
Date:	Sat, 5 Dec 2015 00:15:58 -0600
From:	Seth Forshee <seth.forshee@...onical.com>
To:	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-bcache@...r.kernel.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	fuse-devel@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov
Subject: Re: [PATCH 14/19] fs: Permit FIBMAP for users with CAP_SYS_RAWIO in
 s_user_ns

On Fri, Dec 04, 2015 at 05:43:49PM -0600, Serge E. Hallyn wrote:
> On Fri, Dec 04, 2015 at 06:11:52PM -0500, Theodore Ts'o wrote:
> > On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:
> > > On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:
> > > > Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
> > > > a little while ago :)  The same question was asked 16 years ago.  Apparently
> > > > the answer then was that it was easier than fixing the code.
> > > 
> > > So it seems then that either it still isn't safe and so unprivileged
> > > users shouldn't be allowed to do it at all, or else it's safe and we
> > > should drop the requirement completely. I can't say which is right,
> > > unfortunately.
> > 
> > It may not have been safe 16 years agoo, but giving invalid arguments
> > to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
> > tools like trinity should and does test for, so I think it should be
> > fine to remove the root check for FIBMAP.
> 
> Seth, can I tempt you into sending a standalone patch to remove that? :)

Patch sent. I'll drop this patch in v2.
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