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

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Message-ID: <CAMuHMdXciS54ZZA2TV3+JZP7szHyGOhbrdQ_1rEYUwx2YSO+Qg@mail.gmail.com>
Date:	Tue, 28 Jan 2014 13:17:22 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Ingo Molnar <mingo@...nel.org>, Joe Perches <joe@...ches.com>
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 Tue, Jan 28, 2014 at 1:04 PM, Ingo Molnar <mingo@...nel.org> wrote:
> * Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> 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?
>
> Correct - and in fact that kind of limitation is also a security
> feature: using patterns _outside_ of the typical, already defined
> group of permission patterns would in itself be a 'is that really
> justified?' red flag during review.

Then Joe (CCed :-) can write a checkpatch rule to flag all new users of the
I_S[RWX}* flags..,

> I'm fine with Alexey's shorter variant as well.
>
> Would someone be interested in sending a real patch for it, defining a
> usable set of initial flags such as 0644, 0444, 0555 and 0600?

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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