linux-kernel - Re: [PATCH] kernel: escape non-ASCII and control characters in printk()

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Date:	Mon, 11 Jul 2011 06:37:20 +0000
From:	Pavel Machek <pavel@....cz>
To:	Greg KH <gregkh@...e.de>
Cc:	Vasiliy Kulikov <segoon@...nwall.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...il.com>,
	kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
	security@...nel.org
Subject: Re: [PATCH] kernel: escape non-ASCII and control characters in
	printk()

On Wed 2011-06-22 08:37:42, Greg KH wrote:
> On Wed, Jun 22, 2011 at 01:53:41PM +0400, Vasiliy Kulikov wrote:
> > This patch escapes all characters outside of allowed '\n' plus 0x20-0x7E
> > charset passed to printk().
> > 
> > There are numerous printk() instances with user supplied input as "%s"
> > data, and unprivileged user may craft log messages with substrings
> > containing control characters via these printk()s.  Control characters
> > might fool root viewing the logs via tty.
> 
> There are "numerous" places this could happen?  Shouldn't this be
> handled by the viewers of the log file and not the kernel itself?

well, currently cat /proc/kmsg is bad idea on multiuser system... right?

> And what could these control characters cause to be "fooled"?

terminals are powerful (or shall we say insecure?) these days. Including replies.

cat /proc/kmsg can result in something like "9q" be added to the next
bash command. It would not surprise me if nastier stuff was possible
with some xterm variant.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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