Ack: [Lucid][CVE-2013-0343] ipv6: remove max_addresses check from ipv6_create_tempaddr

[Steve Conklin]

On 09/11/2013 09:01 AM, Luis Henriques wrote:
> From: Hannes Frederic Sowa <hannes at stressinduktion.org>
> 
> BugLink: http://bugs.launchpad.net/bugs/1143800
> 
> CVE-2013-0343
> 
> Because of the max_addresses check attackers were able to disable privacy
> extensions on an interface by creating enough autoconfigured addresses:
> 
> <http://seclists.org/oss-sec/2012/q4/292>
> 
> But the check is not actually needed: max_addresses protects the
> kernel to install too many ipv6 addresses on an interface and guards
> addrconf_prefix_rcv to install further addresses as soon as this limit
> is reached. We only generate temporary addresses in direct response of
> a new address showing up. As soon as we filled up the maximum number of
> addresses of an interface, we stop installing more addresses and thus
> also stop generating more temp addresses.
> 
> Even if the attacker tries to generate a lot of temporary addresses
> by announcing a prefix and removing it again (lifetime == 0) we won't
> install more temp addresses, because the temporary addresses do count
> to the maximum number of addresses, thus we would stop installing new
> autoconfigured addresses when the limit is reached.
> 
> This patch fixes CVE-2013-0343 (but other layer-2 attacks are still
> possible).
> 
> Thanks to Ding Tianhong to bring this topic up again.
> 
> Cc: Ding Tianhong <dingtianhong at huawei.com>
> Cc: George Kargiotakis <kargig at void.gr>
> Cc: P J P <ppandit at redhat.com>
> Cc: YOSHIFUJI Hideaki <yoshfuji at linux-ipv6.org>
> Signed-off-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
> Acked-by: Ding Tianhong <dingtianhong at huawei.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> (back ported from commit 4b08a8f1bd8cb4541c93ec170027b4d0782dab52)
> Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> ---
>  net/ipv6/addrconf.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index e23be1f..c0a47ec 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -920,12 +920,10 @@ retry:
>  	if (ifp->flags & IFA_F_OPTIMISTIC)
>  		addr_flags |= IFA_F_OPTIMISTIC;
>  
> -	ift = !max_addresses ||
> -	      ipv6_count_addresses(idev) < max_addresses ?
> -		ipv6_add_addr(idev, &addr, tmp_plen,
> -			      ipv6_addr_type(&addr)&IPV6_ADDR_SCOPE_MASK,
> -			      addr_flags) : NULL;
> -	if (!ift || IS_ERR(ift)) {
> +	ift = ipv6_add_addr(idev, &addr, tmp_plen,
> +			    ipv6_addr_type(&addr)&IPV6_ADDR_SCOPE_MASK,
> +			    addr_flags);
> +	if (IS_ERR(ift)) {
>  		in6_ifa_put(ifp);
>  		in6_dev_put(idev);
>  		printk(KERN_INFO
>