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

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Date:	Tue, 28 Jan 2014 09:39:46 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH] afs: proc cells and rootcell are writeable

On Sun, Jan 26, 2014 at 9:25 PM, Ingo Molnar <mingo@...nel.org> wrote:
> * Ingo Molnar <mingo@...nel.org> wrote:
>> * 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

I like it (also without the PERM prefix, cfr. Alexey's old patch).

>> or something similar, more or less matching the output of 'ls -l'?
>
> Another variant of this would be to do the following macro:
>
>         PERM(R_X, R_X, R_X)
>         PERM(R__, R__, R__)
>         PERM(RW_, R__, R__)

IMHO, this is again less outstanding.

> With the advantage of separating the groups better and reducing the
> number of constants needed.

Only a limited number of combinations is in active use, right?
It should be difficult to create e.g. world-writable files that are
not accessable
by the owner.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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