Patchwork [RESEND] ipv6: add anti-spoofing checks for 6to4 and 6rd

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Submitter Hannes Frederic Sowa
Date Jan. 23, 2013, 10:02 a.m.
Message ID <20130123100248.GB7317@order.stressinduktion.org>
Download mbox | patch
Permalink /patch/214873/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Hannes Frederic Sowa - Jan. 23, 2013, 10:02 a.m.
This patch adds anti-spoofing checks in sit.c as specified in RFC3964
section 5.2 for 6to4 and RFC5969 section 12 for 6rd. I left out the
checks which could easily be implemented with netfilter.

Specifically this patch adds following logic (based loosely on the
pseudocode in RFC3964 section 5.2):

if prefix (inner_src_v6) == rd6_prefix (2002::/16 is the default)
        and outer_src_v4 != embedded_ipv4 (inner_src_v6)
                drop
if prefix (inner_dst_v6) == rd6_prefix (or 2002::/16 is the default)
        and outer_dst_v4 != embedded_ipv4 (inner_dst_v6)
                drop
accept

To accomplish the specified security checks proposed by above RFCs,
it is still necessary to employ uRPF filters with netfilter. These new
checks only kick in if the employed addresses are within the 2002::/16 or
another range specified by the 6rd-prefix (which defaults to 2002::/16).

Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
---
 net/ipv6/sit.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)
YOSHIFUJI Hideaki / 吉藤英明 - Jan. 24, 2013, 3:59 a.m.
(2013年01月23日 19:02), Hannes Frederic Sowa wrote:
> This patch adds anti-spoofing checks in sit.c as specified in RFC3964
> section 5.2 for 6to4 and RFC5969 section 12 for 6rd. I left out the
> checks which could easily be implemented with netfilter.
> 
> Specifically this patch adds following logic (based loosely on the
> pseudocode in RFC3964 section 5.2):
> 
> if prefix (inner_src_v6) == rd6_prefix (2002::/16 is the default)
>         and outer_src_v4 != embedded_ipv4 (inner_src_v6)
>                 drop
> if prefix (inner_dst_v6) == rd6_prefix (or 2002::/16 is the default)
>         and outer_dst_v4 != embedded_ipv4 (inner_dst_v6)
>                 drop
> accept
> 
> To accomplish the specified security checks proposed by above RFCs,
> it is still necessary to employ uRPF filters with netfilter. These new
> checks only kick in if the employed addresses are within the 2002::/16 or
> another range specified by the 6rd-prefix (which defaults to 2002::/16).
> 
> Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
> Cc: David Miller <davem@davemloft.net>
> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
> ---
>  net/ipv6/sit.c | 29 +++++++++++++++++++++++++++--
>  1 file changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
> index cfba99b..5a09f13 100644
> --- a/net/ipv6/sit.c
> +++ b/net/ipv6/sit.c
> @@ -73,6 +73,8 @@ static int ipip6_tunnel_init(struct net_device *dev);
>  static void ipip6_tunnel_setup(struct net_device *dev);
>  static void ipip6_dev_free(struct net_device *dev);
>  static struct rtnl_link_ops sit_link_ops __read_mostly;
> +static inline __be32 try_6rd(const struct in6_addr *v6dst,
> +			     struct ip_tunnel *tunnel);
>  
>  static int sit_net_id __read_mostly;
>  struct sit_net {
> @@ -590,6 +592,22 @@ out:
>  	return err;
>  }
>  
> +static int sit_chk_encap_addr(struct ip_tunnel *tunnel, const __be32 *addr,
> +			      const struct in6_addr *addr6)
> +{
> +#ifdef CONFIG_IPV6_SIT_6RD
> +	if (ipv6_prefix_equal(addr6, &tunnel->ip6rd.prefix,
> +			      tunnel->ip6rd.prefixlen) &&
> +	    *addr != try_6rd(addr6, tunnel))
> +		return 0;
> +#else
> +	if (addr6->s6_addr16[0] == htons(0x2002) &&
> +	    *addr != try_6rd(addr6, tunnel))
> +		return 0;
> +#endif
> +	return 1;
> +}
> +

I need to do more research.  I am still not convinced
to have such destination check here because the standard
seems silent about it, and we have several basic checks
in standard input path and tunnel search.


Anyway, try_6rd() can do check for prefix as well
but we are doing slightly different thing.
So I think we can introduce new __check_6rd() to
return non-6rd/6to4 addresses.

bool __check_6rd(struct ip_tunnel *tunnel,
		 const struct in6_addr *v6dst,
		 __be32 *v4dst);

If prefix matches, fill *v4dst and return true.
Otherwise, return false.

__be32 __try_6rd()
{
	__be32 dst = 0;
	__check_6rd(tunnel, v6dst, &dst);
	return dst;
}

--yoshfuji
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Hannes Frederic Sowa - Jan. 24, 2013, 1:55 p.m.
On Thu, Jan 24, 2013 at 12:59:30PM +0900, YOSHIFUJI Hideaki wrote:
> I need to do more research.  I am still not convinced
> to have such destination check here because the standard
> seems silent about it, and we have several basic checks
> in standard input path and tunnel search.

Thanks, looking forward to your conclusion.

> Anyway, try_6rd() can do check for prefix as well
> but we are doing slightly different thing.
> So I think we can introduce new __check_6rd() to
> return non-6rd/6to4 addresses.
> 
> bool __check_6rd(struct ip_tunnel *tunnel,
> 		 const struct in6_addr *v6dst,
> 		 __be32 *v4dst);
> 
> If prefix matches, fill *v4dst and return true.
> Otherwise, return false.
> 
> __be32 __try_6rd()
> {
> 	__be32 dst = 0;
> 	__check_6rd(tunnel, v6dst, &dst);
> 	return dst;
> }

I'll update the patch and send it over for review, thanks.

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Roman Mamedov - June 27, 2013, 1:49 p.m.
Hannes Frederic Sowa <hannes <at> stressinduktion.org> writes:

> 
> This patch adds anti-spoofing checks in sit.c as specified in RFC3964
> section 5.2 for 6to4 and RFC5969 section 12 for 6rd. I left out the
> checks which could easily be implemented with netfilter.
> 
> Specifically this patch adds following logic (based loosely on the
> pseudocode in RFC3964 section 5.2):
> 
> if prefix (inner_src_v6) == rd6_prefix (2002::/16 is the default)
>         and outer_src_v4 != embedded_ipv4 (inner_src_v6)
>                 drop
> if prefix (inner_dst_v6) == rd6_prefix (or 2002::/16 is the default)
>         and outer_dst_v4 != embedded_ipv4 (inner_dst_v6)
>                 drop
> accept
> 
> To accomplish the specified security checks proposed by above RFCs,
> it is still necessary to employ uRPF filters with netfilter. These new
> checks only kick in if the employed addresses are within the 2002::/16 or
> another range specified by the 6rd-prefix (which defaults to 2002::/16).

Hello,

This broke access to all 6to4 destinations from any unrelated sit tunnels.

For example users of tunnelbroker.net IPv6 tunnel service (2001:470::/32)
can no longer communicate with anyone using 6to4 anywhere on the internet.

In general, any host, routing to/from which happens to traverse a sit
tunnel (using native IPv6 ranges), can no longer successfully send
packets to a 6to4 destination.

Thanks


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Hannes Frederic Sowa - June 27, 2013, 2:19 p.m.
On Thu, Jun 27, 2013 at 01:49:59PM +0000, Roman Mamedov wrote:
> Hannes Frederic Sowa <hannes <at> stressinduktion.org> writes:
> 
> > 
> > This patch adds anti-spoofing checks in sit.c as specified in RFC3964
> > section 5.2 for 6to4 and RFC5969 section 12 for 6rd. I left out the
> > checks which could easily be implemented with netfilter.
> > 
> > Specifically this patch adds following logic (based loosely on the
> > pseudocode in RFC3964 section 5.2):
> > 
> > if prefix (inner_src_v6) == rd6_prefix (2002::/16 is the default)
> >         and outer_src_v4 != embedded_ipv4 (inner_src_v6)
> >                 drop
> > if prefix (inner_dst_v6) == rd6_prefix (or 2002::/16 is the default)
> >         and outer_dst_v4 != embedded_ipv4 (inner_dst_v6)
> >                 drop
> > accept
> > 
> > To accomplish the specified security checks proposed by above RFCs,
> > it is still necessary to employ uRPF filters with netfilter. These new
> > checks only kick in if the employed addresses are within the 2002::/16 or
> > another range specified by the 6rd-prefix (which defaults to 2002::/16).
> 
> This broke access to all 6to4 destinations from any unrelated sit tunnels.
> 
> For example users of tunnelbroker.net IPv6 tunnel service (2001:470::/32)
> can no longer communicate with anyone using 6to4 anywhere on the internet.
> 
> In general, any host, routing to/from which happens to traverse a sit
> tunnel (using native IPv6 ranges), can no longer successfully send
> packets to a 6to4 destination.

Hmpf. :/

Indeed, I will revisit the patch. I had several test-cases with 6rd and 6to4
but tested static tunnel configs only once.

I'll try to provide a fix as soon as I am at home again.

Sorry and thanks for the report,

  Hannes

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Patch

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index cfba99b..5a09f13 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -73,6 +73,8 @@  static int ipip6_tunnel_init(struct net_device *dev);
 static void ipip6_tunnel_setup(struct net_device *dev);
 static void ipip6_dev_free(struct net_device *dev);
 static struct rtnl_link_ops sit_link_ops __read_mostly;
+static inline __be32 try_6rd(const struct in6_addr *v6dst,
+			     struct ip_tunnel *tunnel);
 
 static int sit_net_id __read_mostly;
 struct sit_net {
@@ -590,6 +592,22 @@  out:
 	return err;
 }
 
+static int sit_chk_encap_addr(struct ip_tunnel *tunnel, const __be32 *addr,
+			      const struct in6_addr *addr6)
+{
+#ifdef CONFIG_IPV6_SIT_6RD
+	if (ipv6_prefix_equal(addr6, &tunnel->ip6rd.prefix,
+			      tunnel->ip6rd.prefixlen) &&
+	    *addr != try_6rd(addr6, tunnel))
+		return 0;
+#else
+	if (addr6->s6_addr16[0] == htons(0x2002) &&
+	    *addr != try_6rd(addr6, tunnel))
+		return 0;
+#endif
+	return 1;
+}
+
 static int ipip6_rcv(struct sk_buff *skb)
 {
 	const struct iphdr *iph;
@@ -613,8 +631,15 @@  static int ipip6_rcv(struct sk_buff *skb)
 		skb->protocol = htons(ETH_P_IPV6);
 		skb->pkt_type = PACKET_HOST;
 
-		if ((tunnel->dev->priv_flags & IFF_ISATAP) &&
-		    !isatap_chksrc(skb, iph, tunnel)) {
+		if (tunnel->dev->priv_flags & IFF_ISATAP) {
+			if (!isatap_chksrc(skb, iph, tunnel)) {
+				tunnel->dev->stats.rx_errors++;
+				goto out;
+			}
+		} else if (!sit_chk_encap_addr(tunnel, &iph->saddr,
+					       &ipv6_hdr(skb)->saddr) ||
+			   !sit_chk_encap_addr(tunnel, &iph->daddr,
+					       &ipv6_hdr(skb)->daddr)) {
 			tunnel->dev->stats.rx_errors++;
 			goto out;
 		}