Subject: Re: [PATCH 1/2] ipv6: do not disable temp_address when reaching max_address

From: Sergei Shtylyov <[email-masked]>
Date: Tue, 13 Aug 2013 18:31:11 +0400

Hello.

On 08/13/2013 10:14 AM, 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

> Signed-off-by: Ding Tianhong <[email-masked]>
> Tested-by: Wang Weidong <[email-masked]>
> Cc: David S. Miller <[email-masked]>
> ---
>   net/ipv6/addrconf.c | 25 +++++++++++++++++++++----
>   1 file changed, 21 insertions(+), 4 deletions(-)

> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index da4241c..99f9fd5 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1134,10 +1134,27 @@ retry:
[...]
> +		if (PTR_ERR(ift) == -EEXIST) {
> +			pr_info("%s: retry temporary address regeneration\n", __func__);
> +			tmpaddr = &addr;
> +			write_lock(&idev->lock);
> +			goto retry;
> +		} else
> +			goto out;

    According to CodingStyle, both arms of the *if* statement should have {} 
if one has it.

WBR, Sergei