linux-kernel - Re: printk()s of user-supplied strings (Re: [PATCH] binfmt_elf.c : the BAD

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Message-Id: <200608222023.k7MKNHpH018036@pasta.boston.redhat.com>
Date:	Tue, 22 Aug 2006 16:23:17 -0400
From:	Ernie Petrides <petrides@...hat.com>
To:	Solar Designer <solar@...nwall.com>
cc:	Willy Tarreau <w@....eu>, linux-kernel@...r.kernel.org
Subject: Re: printk()s of user-supplied strings (Re: [PATCH] binfmt_elf.c : the BAD_ADDR macro again)

On Tuesday, 22-Aug-2006 at 7:7 +0400, Solar Designer wrote:

> On Mon, Aug 21, 2006 at 07:36:01PM -0400, Ernie Petrides wrote:
> > -			printk(KERN_ERR "Unable to load interpreter %.128s\n",
> > -				elf_interpreter);
>
> I'd rather have this message rate-limited, not dropped completely.

I consider any printk() that can be arbitrarily triggered by an
unprivileged user to be inappropriate, rate-limited or not.  I
recommend that it be removed entirely.

> Another long-time concern that I had is that we've got some printk()s
> of user-supplied string data.  What about embedded linefeeds - can this
> be used to produce fake kernel messages with arbitrary log level (syslog
> priority)?  It certainly seems so.
>
> Also, there are terminal controls...

These are valid concerns.  Allowing the kernel to print user-fabricated
strings is a terrible idea.

Cheers.  -ernie
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