linux-kernel - Re: [PATCH] sysctl: terminate strings also on \r

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Message-ID: <CAMuHMdVeFGjti-6ghv_u6_r2HkKHwWj70TGzQ0yGkuTmu7zBLQ@mail.gmail.com>
Date:	Mon, 27 Oct 2014 11:11:53 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Pavel Machek <pavel@....cz>
Cc:	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Aaron Tomlin <atomlin@...hat.com>,
	Dario Faggioli <raistlin@...ux.it>,
	Andi Kleen <ak@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jens Axboe <axboe@...com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Wise <pabs3@...edaddy.net>
Subject: Re: [PATCH] sysctl: terminate strings also on \r

On Mon, Oct 27, 2014 at 10:56 AM, Pavel Machek <pavel@....cz> wrote:
> On Wed 2014-10-22 16:43:10, Kees Cook wrote:
>> On Wed, Oct 22, 2014 at 4:26 PM, Andrew Morton
>> <akpm@...ux-foundation.org> wrote:
>> > On Tue, 21 Oct 2014 13:21:37 -0700 Kees Cook <keescook@...omium.org> wrote:
>> >
>> >> From: Paul Wise <pabs3@...edaddy.net>
>> >>
>> >> This partially mitigates a common strategy used by attackers for hiding
>> >> the full contents of strings in procfs from naive sysadmins who use cat,
>> >> more or sysctl to inspect the contents of strings in procfs.
>> >>
>> >> ...
>> >>
>> >> --- a/kernel/sysctl.c
>> >> +++ b/kernel/sysctl.c
>> >> @@ -1739,7 +1739,7 @@ static int _proc_do_string(char *data, int maxlen, int write,
>> >>               while ((p - buffer) < *lenp && len < maxlen - 1) {
>> >>                       if (get_user(c, p++))
>> >>                               return -EFAULT;
>> >> -                     if (c == 0 || c == '\n')
>> >> +                     if (c == 0 || c == '\n' || c == '\r')
>> >>                               break;
>> >>                       data[len++] = c;
>> >>               }
>> >
>> > There are no valid uses of \r in a procfs write?
>>
>> I struggle to imagine one; everything I found that uses proc_dostring
>> seems to be names, paths, and commands.
>
> Well, filename can contain \r, right?

Even \n. AFAIK, the only thing a filename cannot contain is the nul character
and a forward slash, as that's used to separate path components (so slash
is valid for a path name).

Still, we can hide stuff using ANSI ESC sequences, and e.g. backspaces,
right?

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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