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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGXu5jL-6sGy2QSH39Qmu0-8MEg6aX5GCPvPKeWaheXcai0TDA@mail.gmail.com>
Date:	Thu, 23 Oct 2014 09:39:09 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Paul Wise <pabs3@...edaddy.net>,
	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>
Subject: Re: [PATCH] sysctl: terminate strings also on \r

On Wed, Oct 22, 2014 at 7:00 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 22 Oct 2014 16:43:10 -0700 Kees Cook <keescook@...omium.org> 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.
>>
>
> You're insufficiently pessimistic.

Haha, I haven't had that accusation made about me before; I'll keep
this quote around! :)

> I wonder if the chances of damage would be lower if we were to continue
> to accept the \r, but turn it into something else ("\r"?) when it is
> read.

I think that would complicate things more than help them. If there's a
legit use of \r, I'll let Paul Wise debate how to proceed. :)

-Kees

-- 
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/