netdev - Re: [PATCH 1/3 v4] ipv6: do not disable temp_address when reaching max

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Date:	Thu, 15 Aug 2013 03:24:57 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Ding Tianhong <dingtianhong@...wei.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jon Maloy <jon.maloy@...csson.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Netdev <netdev@...r.kernel.org>, kargig@...d.gr,
	ppandit@...hat.com
Subject: Re: [PATCH 1/3 v4] ipv6: do not disable temp_address when reaching max_address

On Thu, Aug 15, 2013 at 08:43:06AM +0800, Ding Tianhong wrote:
> On 2013/8/14 18:15, Hannes Frederic Sowa wrote:
> > 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 <dingtianhong@...wei.com>
> >> Tested-by: Wang Weidong <wangweidong1@...wei.com>
> >> Cc: David S. Miller <davem@...emloft.net>
> >> Cc: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> >> Cc: Eric Dumazet <edumazet@...gle.com>
> >> ---
> >>  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
> > 
> > 
> ok, thanks for your feedback, I'll waiting you for more information to fix the problem.:)

[added George Kargiotakis and P J P to Cc and full quote]

I wonder if the easiest solution would be to just drop the max_addresses
limit from ipv6_create_tempaddr. max_addresses protects the kernel from
installing an unlimited amount of addresses on an interface which gets flooded
by RAs. Because we have a direct relation between interface address to temp
address, I don't see that we would create the possiblity of DoS.

Sure, an audit and testing is needed.

Greetings,

  Hannes

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