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* Re: [PATCH] net: clear heap allocations for privileged ethtool actions
From: Eric Dumazet @ 2010-10-07 21:31 UTC (permalink / raw)
  To: Kees Cook
  Cc: linux-kernel, David S. Miller, Ben Hutchings, Jeff Garzik,
	Jeff Kirsher, Peter P Waskiewicz Jr, netdev
In-Reply-To: <20101007211004.GA20267@outflux.net>

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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