linux-kernel - Re: [PATCH 1/5] fs: Verify access of user towards block device file when mounting

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Date:	Thu, 1 Oct 2015 10:55:09 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Kent Overstreet <kent.overstreet@...il.com>,
	Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
	Neil Brown <neilb@...e.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	linux-bcache@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: [PATCH 1/5] fs: Verify access of user towards block device file
 when mounting

On Thu, Oct 01, 2015 at 10:40:08AM -0500, Eric W. Biederman wrote:
> Seth Forshee <seth.forshee@...onical.com> writes:
> 
> > When mounting a filesystem on a block device there is currently
> > no verification that the user has appropriate access to the
> > device file passed to mount. This has not been an issue so far
> > since the user in question has always been root, but this must
> > be changed before allowing unprivileged users to mount in user
> > namespaces.
> >
> > To fix this, add an argument to lookup_bdev() to specify the
> > required permissions. If the mask of permissions is zero, or
> > if the user has CAP_SYS_ADMIN, the permission check is skipped,
> > otherwise the lookup fails if the user does not have the
> > specified access rights for the inode at the supplied path.
> >
> > Callers associated with mounting are updated to pass permission
> > masks to lookup_bdev() so that these mounts will fail for an
> > unprivileged user who lacks permissions for the block device
> > inode. All other callers pass 0 to maintain their current
> > behaviors.
> >
> 
> Seth can you split this patch?
> 
> One patch to add an argument to lookup_bdev,
> and then for each kind of callsite a follow-on patch (if we are ready
> for that).
> 
> That will separate the logical changes and make things easier to track
> via bisect and more importantly easier to review things.

Sure, I'll do that.

Seth
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