Subject: Re: [PATCH 1/3 v4] ipv6: do not disable temp_address when reaching max_address

From: Hannes Frederic Sowa <[email-masked]>
Date: Wed, 14 Aug 2013 12:15:11 +0200

On Wed, Aug 14, 2013 at 05:06:54PM +0800, Ding Tianhong wrote:
> A LAN user can remotely disable temporary address which may lead
> to privacy violatins and information disclosure.
> 
> The reason is that the linux kernel uses the 'ipv6.max_addresses'
> option to specify how many ipv6 addresses and interface may have.
> The 'ipv6.regen_max_retry' (default value 3) option specifies
> how many times the kernel will try to create a new address.
> 
> But the kernel is not distinguish between the event of reaching
> max_addresses for an interface and failing to generate a new address.
> the kernel disable the temporary address after regenerate a new
> address 'regen_max_retry' times.
> 
> According RFC4941 3.3.7:
> 
> ---------------------------------------
> 
> If DAD indicates the address is already in use,
> the node must generate a new randomized interface
> identifier as described in section 3.2 above, and
> repeat the previous steps as appropriate up to
> TEMP_IDGEN_RETRIES times.
> 
> If after TEMP_IDGEN_RETRIES consecutive attempts no
> non-unique address was generated, the node must log
> a system error and must not attempt to generate
> temporary address for that interface.
> 
> ------------------------------------------
> 
> RFC4941 3.3.7 specifies that disabling the temp_address must happen
> upon the address is already in use, not reach the max_address,
> So we have to check the return err and distinguish the correct retry path.
> 
> This fixes CVE-2013-0343

I don't think this patch fixes CVE-2013-0343.

> 
> Signed-off-by: Ding Tianhong <[email-masked]>
> Tested-by: Wang Weidong <[email-masked]>
> Cc: David S. Miller <[email-masked]>
> Cc: Sergei Shtylyov <[email-masked]>
> Cc: Eric Dumazet <[email-masked]>
> ---
>  net/ipv6/addrconf.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index da4241c..7b55464 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1134,10 +1134,28 @@ retry:
>  	if (IS_ERR_OR_NULL(ift)) {
>  		in6_ifa_put(ifp);
>  		in6_dev_put(idev);
> -		pr_info("%s: retry temporary address regeneration\n", __func__);
> -		tmpaddr = &addr;
> -		write_lock(&idev->lock);
> -		goto retry;
> +
> +		/* According RFC4941 3.3.7:
> +		 * If DAD indicates the address is already in use,
> +		 * the node must generate a new randomized interface
> +		 * identifier as described in section 3.2 above, and
> +		 * repeat the previous steps as appropriate up to
> +		 * TEMP_IDGEN_RETRIES times.
> +		 * If after TEMP_IDGEN_RETRIES consecutive attempts no
> +		 * non-unique address was generated, the node must log
> +		 * a system error and must not attempt to generate
> +		 * temporary address for that interface.
> +		 * So we have to check the return err and distinguish
> +		 * the correct retry path.
> +		 */
> +		if (PTR_ERR(ift) == -EEXIST) {

-EEXIST is not the same as "ipv6 address is is already used on the
subnet". I really don't see the point here. IMHO this breaks the intended
regeneration logic.

I fear a fix of CVE-2013-0343 will be a bit more complicated. ;) I give it a
thought.

Greetings,

  Hannes