netdev - RE: [patch -stable] igbvf: integer wrapping bug setting the mtu

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Date:	Fri, 13 Sep 2013 09:58:25 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Dan Carpenter" <dan.carpenter@...cle.com>,
	"Jeff Kirsher" <jeffrey.t.kirsher@...el.com>
Cc:	"Jesse Brandeburg" <jesse.brandeburg@...el.com>,
	"Bruce Allan" <bruce.w.allan@...el.com>,
	"Carolyn Wyborny" <carolyn.wyborny@...el.com>,
	"Don Skidmore" <donald.c.skidmore@...el.com>,
	"Greg Rose" <gregory.v.rose@...el.com>,
	"Peter P Waskiewicz Jr" <peter.p.waskiewicz.jr@...el.com>,
	"Alex Duyck" <alexander.h.duyck@...el.com>,
	"John Ronciak" <john.ronciak@...el.com>,
	"Tushar Dave" <tushar.n.dave@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Mitch Williams" <mitch.a.williams@...el.com>,
	"Patrick McHardy" <kaber@...sh.net>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	<e1000-devel@...ts.sourceforge.net>, <netdev@...r.kernel.org>,
	<kernel-janitors@...r.kernel.org>
Subject: RE: [patch -stable] igbvf: integer wrapping bug setting the mtu

> If new_mtu is very large then "new_mtu + ETH_HLEN + ETH_FCS_LEN" can
> wrap and the check on the next line can underflow. This is one of those
> bugs which can be triggered by the user if you have namespaces
> configured.
> 
> This is a static checker fix and I'm not sure what the impact is.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> diff --git a/drivers/net/ethernet/intel/igbvf/netdev.c b/drivers/net/ethernet/intel/igbvf/netdev.c
> index 95d5430..24e3883 100644
> --- a/drivers/net/ethernet/intel/igbvf/netdev.c
> +++ b/drivers/net/ethernet/intel/igbvf/netdev.c
> @@ -2342,7 +2342,7 @@ static struct net_device_stats *igbvf_get_stats(struct net_device *netdev)
>  static int igbvf_change_mtu(struct net_device *netdev, int new_mtu)
>  {
>  	struct igbvf_adapter *adapter = netdev_priv(netdev);
> -	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
> +	unsigned int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
> 
>  	if ((new_mtu < 68) || (max_frame > MAX_JUMBO_FRAME_SIZE)) {
>  		dev_err(&adapter->pdev->dev, "Invalid MTU setting\n");

It is safer to check:
  	if ((new_mtu < 68) || (new_mtu > MAX_JUMBO_FRAME_SIZE - ETH_HLEN - ETH_FCS_LEN)) {

	David



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