linux-kernel - Re: [PATCH] afs: proc cells and rootcell are writeable

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Date:	Sun, 26 Jan 2014 21:19:28 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-afs@...ts.infradead.org,
	Pali Rohár <pali.rohar@...il.com>
Subject: Re: [PATCH] afs: proc cells and rootcell are writeable


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Sun, Jan 26, 2014 at 4:27 AM, David Howells <dhowells@...hat.com> wrote:
> >
> > -       p = proc_create("cells", 0, proc_afs, &afs_proc_cells_fops);
> > +       p = proc_create("cells", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_cells_fops);
> > -       p = proc_create("rootcell", 0, proc_afs, &afs_proc_rootcell_fops);
> > +       p = proc_create("rootcell", S_IFREG | S_IRUGO | S_IWUSR, proc_afs, &afs_proc_rootcell_fops);
> 
> So the S_IFREG isn't necessary.
> 
> And quite frankly, I personally think S_IRUGO | S_IWUSR is _less_ 
> readable than 0644. It's damn hard to parse those random letter 
> combinations, and at least I have to really think about it, in a way 
> that the octal representation does *not* make me go "I have to think 
> about that".
> 
> So my personal preference would be to just see that simple 0644 in 
> proc_create. Hmm?

Perhaps we could also generate the most common variants as:

 #define PERM__rw_r__r__		0644
 #define PERM__r________		0400
 #define PERM__r__r__r__		0444
 #define PERM__r_xr_xr_x		0555

etc.

or something similar, more or less matching the output of 'ls -l'?

That would also make security bugs in this area apparent at first 
sight. The number of people who can recognize during review that 
PERM_rw__w__w is probably unwise is probably two orders of magnitude 
than those who can interpret octal 0622 at a glance.

Thanks,

	Ingo
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