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

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Message-Id: <20141022190051.7c0d5df1.akpm@linux-foundation.org>
Date:	Wed, 22 Oct 2014 19:00:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kees Cook <keescook@...omium.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, 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.

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.

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