linux-kernel - Re: [PATCH] pktgen: Remove a dangerous debug print.

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Message-ID: <20101027192808.GP16803@ksplice.com>
Date:	Wed, 27 Oct 2010 15:28:08 -0400
From:	Nelson Elhage <nelhage@...lice.com>
To:	David Miller <davem@...emloft.net>
Cc:	robert.olsson@....uu.se, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, eugene@...hat.com
Subject: Re: [PATCH] pktgen: Remove a dangerous debug print.

How would you feel about limiting the debug print to at most, say, 512 or 1024
bytes? Even if it's only accessible to root by default, I don't a userspace
program should be able to accidentally corrupt the kernel stack by writing too
many bytes to a file in /proc.

- Nelson

On Wed, Oct 27, 2010 at 12:21:43PM -0700, David Miller wrote:
> From: Nelson Elhage <nelhage@...lice.com>
> Date: Wed, 27 Oct 2010 15:13:08 -0400
> 
> > We were allocating an arbitrarily-large buffer on the stack, which would allow a
> > buggy or malicious userspace program to overflow the kernel stack.
> > 
> > Since the debug printk() was just printing exactly the text passed from
> > userspace, it's probably just as easy for anyone who might use it to augment (or
> > just strace(1)) the program writing to the pktgen file, so let's just not bother
> > trying to print the whole buffer.
> > 
> > Signed-off-by: Nelson Elhage <nelhage@...lice.com>
> 
> Only root can write to the pktgen control file.
> 
> Also, the debug feature really is used by people's pktgen scripts, you
> can't just turn it off.
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