于 2013年09月02日 05:08, Hannes Frederic Sowa 写道:

On Sat, Aug 31, 2013 at 01:09:33PM +0800, Duan Jiong wrote:

quoted

RFC 4861 says that the IP source address of the Redirect is the
same as the current first-hop router for the specified ICMP
Destination Address, so the gateway should be taken into
consideration when we find the route for redirect.

Signed-off-by: Duan Jiong <redacted>

This patch looks good!

Maybe you could also point to commit
a6279458c534d01ccc39498aba61c93083ee0372 ("NDISC: Search over all possible
rules on receipt of redirect.") and where the check went away?

The bug is only "exploitable" on layer-2 because the source address of the
redirect is checked to be a valid link-local address but it makes spoofing a
lot easier in the same L2 domain nonetheless.

Nice work!

Some smaller comments inline:

Thanks very much for you comments， and i will correct those problems.

quoted

---
 Changes for v3:
 1.Fix the comments style problems

 net/ipv6/ah6.c     |  2 +-
 net/ipv6/esp6.c    |  2 +-
 net/ipv6/icmp.c    |  2 +-
 net/ipv6/ipcomp6.c |  2 +-
 net/ipv6/ndisc.c   |  3 ++-
 net/ipv6/route.c   | 78 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 6 files changed, 78 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index bb02e17..73784c3 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c

@@ -628,7 +628,7 @@ static void ah6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		return;
 
 	if (type == NDISC_REDIRECT)
-		ip6_redirect(skb, net, 0, 0);
+		ip6_redirect(skb, net, skb->dev->ifindex, 0);
 	else
 		ip6_update_pmtu(skb, net, info, 0, 0);
 	xfrm_state_put(x);

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index aeac0dc..d3618a7 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c

@@ -447,7 +447,7 @@ static void esp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		return;
 
 	if (type == NDISC_REDIRECT)
-		ip6_redirect(skb, net, 0, 0);
+		ip6_redirect(skb, net, skb->dev->ifindex, 0);
 	else
 		ip6_update_pmtu(skb, net, info, 0, 0);
 	xfrm_state_put(x);

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 7cfc8d2..73681c2 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c

@@ -92,7 +92,7 @@ static void icmpv6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 	if (type == ICMPV6_PKT_TOOBIG)
 		ip6_update_pmtu(skb, net, info, 0, 0);
 	else if (type == NDISC_REDIRECT)
-		ip6_redirect(skb, net, 0, 0);
+		ip6_redirect(skb, net, skb->dev->ifindex, 0);
 
 	if (!(type & ICMPV6_INFOMSG_MASK))
 		if (icmp6->icmp6_type == ICMPV6_ECHO_REQUEST)

diff --git a/net/ipv6/ipcomp6.c b/net/ipv6/ipcomp6.c
index 7af5aee..5636a91 100644
--- a/net/ipv6/ipcomp6.c
+++ b/net/ipv6/ipcomp6.c

@@ -76,7 +76,7 @@ static void ipcomp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 		return;
 
 	if (type == NDISC_REDIRECT)
-		ip6_redirect(skb, net, 0, 0);
+		ip6_redirect(skb, net, skb->dev->ifindex, 0);
 	else
 		ip6_update_pmtu(skb, net, info, 0, 0);
 	xfrm_state_put(x);

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 04d31c2..90f474b 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c

@@ -1370,7 +1370,8 @@ static void ndisc_redirect_rcv(struct sk_buff *skb)
 		return;
 
 	if (!ndopts.nd_opts_rh) {
-		ip6_redirect_no_header(skb, dev_net(skb->dev), 0, 0);
+		ip6_redirect_no_header(skb, dev_net(skb->dev),
+							skb->dev->ifindex, 0);

This is not indented correctly. skb->dev->ifindex should be placed right below
the upper skb variable.

quoted

 		return;
 	}
 

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 8d9a93e..2e1d378 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -1157,6 +1157,74 @@ void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, __be32 mtu)
 }
 EXPORT_SYMBOL_GPL(ip6_sk_update_pmtu);
 
+/* Handle redirects */
+struct ip6rd_flowi {
+	struct flowi6 fl6;
+	struct in6_addr gateway;
+};
+
+static struct rt6_info *__ip6_route_redirect(struct net *net,
+					     struct fib6_table *table,
+					     struct flowi6 *fl6,
+					     int flags)
+{
+	struct ip6rd_flowi *rdfl = (struct ip6rd_flowi *)fl6;
+	struct rt6_info *rt;
+	struct fib6_node *fn;
+
+	/* Get the "current" route for this destination and
+	 * check if the redirect has come from approriate router.
+	 *
+	 * RFC 4861 specifies that redirects should only be
+	 * accepted if they come from the nexthop to the target.
+	 * Due to the way the routes are chosen, this notion
+	 * is a bit fuzzy and one might need to check all possible
+	 * routes.
+	 */
+
+	read_lock_bh(&table->tb6_lock);
+	fn = fib6_lookup(&table->tb6_root, &fl6->daddr, &fl6->saddr);
+restart:
+	for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+		if (rt6_check_expired(rt))
+			continue;

[1] (backreference for a comment below)

quoted

+		if (!(rt->rt6i_flags & RTF_GATEWAY))
+			continue;
+		if (fl6->flowi6_oif != rt->dst.dev->ifindex)
+			continue;
+		if (!ipv6_addr_equal(&rdfl->gateway, &rt->rt6i_gateway))
+			continue;
+		break;
+	}
+
+	if (!rt)
+		rt = net->ipv6.ip6_null_entry;
+	BACKTRACK(net, &fl6->saddr);
+out:
+	dst_hold(&rt->dst);
+
+	read_unlock_bh(&table->tb6_lock);
+
+	return rt;
+};
+
+static struct dst_entry *ip6_route_redirect(const struct flowi6 *fl6,
+					   const struct in6_addr *gateway,
+					   struct net *net)

The ordering of the arguments could be in the same style as the other
ip6_route_* functions (net, flow, gateway). But that is not that important.

quoted

+{
+	int flags = RT6_LOOKUP_F_HAS_SADDR;
+	struct ip6rd_flowi rdfl;
+
+	rdfl.fl6 = *fl6;
+	rdfl.gateway = *gateway;
+
+	if (rt6_need_strict(&fl6->daddr))
+		flags |= RT6_LOOKUP_F_IFACE;

This is not needed because you do the matching on interfaces yourself
in __ip6_route_redirect. The flag should currently not be checked on
this code path down in fib6_rule_lookup.

quoted

+
+	return fib6_rule_lookup(net, &rdfl.fl6,
+						   flags, __ip6_route_redirect);

This line jumped a bit too far to the right, too. ;)

quoted

+}
+
 void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark)

Maybe we should rename oif to iif now?

Yes, that looks no ambiguity.

quoted

 {
 	const struct ipv6hdr *iph = (struct ipv6hdr *) skb->data;

@@ -1171,9 +1239,8 @@ void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark)
 	fl6.saddr = iph->saddr;
 	fl6.flowlabel = ip6_flowinfo(iph);
 
-	dst = ip6_route_output(net, NULL, &fl6);
-	if (!dst->error)
-		rt6_do_redirect(dst, NULL, skb);
+	dst = ip6_route_redirect(&fl6, &ipv6_hdr(skb)->saddr, net);
+	rt6_do_redirect(dst, NULL, skb);

What is the reason you left out the dst.error check? E.g. if a system had a
prohbit rule it is possible to circumvent this with a redirect packet now.

That's my fault. i just understand the meaning of dst.error incorrectly, and
i will modify the patch according to your comment below.

I would think about placing this check at [1] and fail the lookup
early. rt6_do_redirect does check for null-entry, so you could omit the
check here, then.

Thanks,
  Duan