linux-kernel - Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces

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Date:	Fri, 25 Feb 2011 12:57:09 -0800
From:	Greg KH <greg@...ah.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Dan Carpenter <error27@...il.com>, Greg KH <gregkh@...e.de>,
	Kees Cook <kees.cook@...onical.com>,
	linux-kernel@...r.kernel.org, Eugene Teo <eugeneteo@...nel.sg>,
	Ralph Campbell <infinipath@...gic.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, Matthew Wilcox <matthew@....cx>,
	James Morris <jmorris@...ei.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>,
	Nick Piggin <npiggin@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
	Ian Campbell <ian.campbell@...rix.com>,
	Jarkko Sakkinen <ext-jarkko.2.sakkinen@...ia.com>,
	Tejun Heo <tj@...nel.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH 2/2] debugfs: only allow root access to debugging
 interfaces

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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