netdev - Re: [PATCH] net: clear heap allocations for privileged ethtool actions

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Date:	Thu, 07 Oct 2010 23:31:25 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Jeff Garzik <jgarzik@...hat.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH] net: clear heap allocations for privileged ethtool
 actions

Le jeudi 07 octobre 2010 à 14:10 -0700, Kees Cook a écrit :
> Several other ethtool functions leave heap uncleared (potentially) by
> drivers. Some interfaces appear safe (eeprom, etc), in that the sizes
> are well controlled. In some situations (e.g. unchecked error conditions),
> the heap will remain unchanged in areas before copying back to userspace.
> Note that these are less of an issue since these all require CAP_NET_ADMIN.

> @@ -775,7 +775,7 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
>  	if (regs.len > reglen)
>  		regs.len = reglen;
>  
> -	regbuf = kmalloc(reglen, GFP_USER);
> +	regbuf = kzalloc(reglen, GFP_USER);
>  	if (!regbuf)
>  		return -ENOMEM;
>  
> -- 
> 1.7.1
> 

Are you sure this is not hiding a more problematic problem ?

Code does :

reglen = ops->get_regs_len(dev);
if (regs.len > reglen)
	regs.len = reglen;
regbuf = kmalloc(reglen, GFP_USER);

So we can not copy back kernel memory.

However, what happens if user provides regs.len = 1 byte, and driver
get_regs() doesnt properly checks regs.len and write past end of regbuf
-> We probably write on other parts of kernel memory

An audit is needed, but first driver I checked is buggy
(drivers/net/qlcnic/qlcnic_ethtool.c)

->
 	memset(p, 0, qlcnic_get_regs_len(dev));



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