netdev - Re: [PATCH] e1000: enhance frame fragment detection

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Date:	Tue, 5 Jan 2010 13:44:25 -0800 (Pacific Standard Time)
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	Neil Horman <nhorman@...driver.com>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] e1000: enhance frame fragment detection

Neil, I couple of comments below, I was just looking at the implementation 
of this for e1000e.

On Mon, 28 Dec 2009, Neil Horman wrote:

> Hey all-
> 	A security discussion was recently given:
> http://events.ccc.de/congress/2009/Fahrplan//events/3596.en.html
> And a patch that I submitted awhile back was brought up.  Apparently some of
> their testing revealed that they were able to force a buffer fragment in e1000
> in which the trailing fragment was greater than 4 bytes.  As a result the
> fragment check I introduced failed to detect the fragement and a partial invalid
> frame was passed up into the network stack.  I've written this patch to correct
> it.  I'm in the process of testing it now, but it makes good logical sense to
> me.  Effectively it maintains a per-adapter state variable which detects a
> non-EOP frame, and discards it and subsequent non-EOP frames leading up to _and_
> _including_ the next positive-EOP frame (as it is by definition the last
> fragment).  This should prevent any and all partial frames from entering the
> network stack from e1000
> 
> Regards
> Neil
> 
> 
>  e1000.h      |    3 ++-
>  e1000_main.c |   14 ++++++++++++--
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/drivers/net/e1000/e1000.h b/drivers/net/e1000/e1000.h
> index 2a567df..3d421ab 100644
> --- a/drivers/net/e1000/e1000.h
> +++ b/drivers/net/e1000/e1000.h
> @@ -331,7 +331,8 @@ struct e1000_adapter {
>  enum e1000_state_t {
>  	__E1000_TESTING,
>  	__E1000_RESETTING,
> -	__E1000_DOWN
> +	__E1000_DOWN,
> +	__E1000_DISCARDING
>  };
>  
>  extern char e1000_driver_name[];
> diff --git a/drivers/net/e1000/e1000_main.c b/drivers/net/e1000/e1000_main.c
> index 7e855f9..0731779 100644
> --- a/drivers/net/e1000/e1000_main.c
> +++ b/drivers/net/e1000/e1000_main.c
> @@ -3850,16 +3850,26 @@ static bool e1000_clean_rx_irq(struct e1000_adapter *adapter,
>  
>  		length = le16_to_cpu(rx_desc->length);
>  		/* !EOP means multiple descriptors were used to store a single
> -		 * packet, also make sure the frame isn't just CRC only */
> -		if (unlikely(!(status & E1000_RXD_STAT_EOP) || (length <= 4))) {
> +		 * packet, if thats the case we need to toss it.  In fact, we
> +		 * to toss every packet with the EOP bit clear and the next
> +		 * frame that _does_ have the EOP bit set, as it is by
> +		 * definition only a frame fragment
> +		 */
> +		if (unlikely(!(status & E1000_RXD_STAT_EOP)))
> +			set_bit(__E1000_DISCARDING, &adapter->flags);

test_bit and set_bit and clear_bit are atomic operations, isn't that quite 
a bit of overhead for something that is already being done in a guaranteed 
single context?

> +
> +		if (test_bit(__E1000_DISCARDING, &adapter->flags)) {
>  			/* All receives must fit into a single buffer */
>  			E1000_DBG("%s: Receive packet consumed multiple"
>  				  " buffers\n", netdev->name);
>  			/* recycle */
>  			buffer_info->skb = skb;
> +			if (status & E1000_RXD_STAT_EOP)
> +				clear_bit(__E1000_DISCARDING, &adapter->flags);

couldn't these simply be read/modify/write assignments (aka |=)

That would significantly avoid the extra cycles needed to implement three 
atomic ops.
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