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

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Date:	Wed, 22 Oct 2014 16:43:10 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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 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.

-Kees

-- 
Kees Cook
Chrome OS Security
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