Date: Fri, 25 Feb 2011 12:57:09 -0800
From: Greg KH <greg@kroah.com>
To: Hugh Dickins <hughd@google.com>
Cc: Dan Carpenter <error27@gmail.com>, Greg KH <gregkh@suse.de>,
        Kees Cook <kees.cook@canonical.com>, linux-kernel@vger.kernel.org,
        Eugene Teo <eugeneteo@kernel.sg>,
        Ralph Campbell <infinipath@qlogic.com>,
        Roland Dreier <roland@kernel.org>, Sean Hefty <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
        "J. Bruce Fields" <bfields@fieldses.org>, Neil Brown <neilb@suse.de>,
        Matthew Wilcox <matthew@wil.cx>, James Morris <jmorris@namei.org>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Eric Paris <eparis@parisplace.org>, Nick Piggin <npiggin@kernel.dk>,
        Arnd Bergmann <arnd@arndb.de>, Ian Campbell <ian.campbell@citrix.com>,
        Jarkko Sakkinen <ext-jarkko.2.sakkinen@nokia.com>,
        Tejun Heo <tj@kernel.org>, Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging
 interfaces
Message-ID: <20110225205709.GB12928@kroah.com>
References: <1298398198-18482-1-git-send-email-kees.cook@canonical.com>
 <1298398198-18482-2-git-send-email-kees.cook@canonical.com>
 <20110222181613.GU4000@outflux.net>
 <20110222191333.GA9991@suse.de>
 <20110222192248.GX4000@outflux.net>
 <20110222193314.GA11033@suse.de>
 <20110222202915.GC1966@bicker>
 <20110225195657.GA8860@kroah.com>
 <alpine.LSU.2.00.1102251225150.3918@sister.anvils>
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On Fri, Feb 25, 2011 at 12:40:43PM -0800, Hugh Dickins wrote:
> On Fri, 25 Feb 2011, Greg KH wrote:
> > On Tue, Feb 22, 2011 at 11:29:15PM +0300, Dan Carpenter wrote:
> > > On Tue, Feb 22, 2011 at 11:33:14AM -0800, Greg KH wrote:
> > > > Again, let's fix the real problems here, world-writable debugfs files.
> > > 
> > > We could just ban them?
> > > 
> > > diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> > > index e7a7a2f..03ae095 100644
> > > --- a/fs/debugfs/inode.c
> > > +++ b/fs/debugfs/inode.c
> > > @@ -223,6 +223,9 @@ struct dentry *debugfs_create_file(const char *name, mode_t mode,
> > >  
> > >  	pr_debug("debugfs: creating file '%s'\n",name);
> > >  
> > > +	/* don't allow world writable files */
> > > +	mode &= ~S_IWOTH;
> > > +
> > >  	error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
> > >  			      &debugfs_mount_count);
> > >  	if (error)
> > > 
> > 
> > I have no objection to this patch, care to resend it with a
> > signed-off-by: so that I can apply it?
> 
> That's funny, I wrote something in debugfs a few months ago which was
> very deliberately rw--w--w-: a kind of circular trace buffer into which
> any userspace could easily echo its progress for debugging.
> 
> Probably won't be upstreamed in that form, nor use debugfs if it is.
> But I mention it as an example of why any such limitation on debugfs
> seems inappropriate to me.

Ok, fair enough, then I'll not add this patch, as you just proved it is
a valuable thing to have world writable debugfs files.

thanks,

greg k-h
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