linux-kernel - Re: [PATCH] sysfs: sysfs_pathname/sysfs_add_one: Use strlcat() instead of strcat()

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Date:	Sun, 30 Sep 2012 20:59:05 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Alex Williamson <alex.williamson@...com>,
	Alex Chiang <achiang@...com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] sysfs: sysfs_pathname/sysfs_add_one: Use strlcat()
 instead of strcat()

Hi Greg,

On Sun, Sep 30, 2012 at 4:49 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Sat, Sep 29, 2012 at 10:23:19PM +0200, Geert Uytterhoeven wrote:
>> The warning check for duplicate sysfs entries can cause a buffer overflow
>> when printing the warning, as strcat() doesn't check buffer sizes.
>> Use strlcat() instead.
>
> As the comment said, we knew about this, but I have never seen it, do
> you know of a way to trigger it?

I expected there would be a check somewhere else in the code, so we can
never overflow here. But I did manage to overflow the buffer by having a real
long name (4060 characters) in a conflicting mfd_cell.
There may be other ways.

I don't know how likely it is to trigger in a real world scenario. Is
there a limit
on the depth of sysfs? Or can it go unbounded, e.g. by cascading USB hubs?

>> Cc: stable@...r.kernel.org
>
> Given that I don't know of any way to actually hit this problem, is it
> really needed for older kernel releases?

That's up to you to decide...

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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