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Message-ID: <20131220130830.GH32361@order.stressinduktion.org>
Date: Fri, 20 Dec 2013 14:08:30 +0100
From: Hannes Frederic Sowa <hannes@...essinduktion.org>
To: netdev@...r.kernel.org
Cc: eric.dumazet@...il.com, davem@...emloft.net
Subject: [PATCH net-next 2/2] ipv6: add forwarding_uses_pmtu knob to protect forward path to use pmtu info
Provide a mode where IPv6 forwarding code does not depend on path MTUs
and just uses interface or per-route locked MTUs to judge whether a
packet should get dropped and a PTB be generated.
Routers can be poisoned with malicious or bogus path MTU information. This
causes the IPv6 stack to generate Packet-Too-Big notifications where
none are needed. If those PTB notifications get blocked later on it
is possible to create blackholes on such routers.
Forwarded skbs are marked with IP6SKB_FORWARDED in ip_forward. This flag
was introduced for multicast forwarding but as it does not conflict with
our usage in the unicast code path it is perfect for reuse.
I needed to move in6_dev_dev around to keep ip6_dst_mtu_secure as a static
inline function in the header and to keep header dependencies happy.
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: David Miller <davem@...emloft.net>
Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
---
v2:
* forwarding_uses_pmtu default to on
* reworded documentation and changelog
Documentation/networking/ip-sysctl.txt | 12 ++++++++++++
include/net/addrconf.h | 32 --------------------------------
include/net/ip6_route.h | 31 ++++++++++++++++++++++++++++---
include/net/ipv6.h | 32 ++++++++++++++++++++++++++++++++
include/net/netns/ipv6.h | 1 +
net/ipv6/af_inet6.c | 2 ++
net/ipv6/ip6_output.c | 3 ++-
net/ipv6/sysctl_net_ipv6.c | 8 ++++++++
8 files changed, 85 insertions(+), 36 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 1077c92..8b32bbc 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1107,6 +1107,18 @@ bindv6only - BOOLEAN
Default: FALSE (as specified in RFC3493)
+forwarding_uses_pmtu - BOOLEAN
+ Don't trust path MTUs while forwarding. Path MTU notifications
+ can easily be forged and lead to unwanted and unnecessary
+ sending of Packet-Too-Big ICMP errors to host systems. If this
+ mode is enabled, only interface and per-route locked MTUs are
+ considered for packet rejection and Packet-Too-Big error
+ generation.
+ Default: 1 (enabled)
+ Possible values:
+ 0 - disabled
+ 1 - enabled
+
IPv6 Fragmentation:
ip6frag_high_thresh - INTEGER
diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 66c4a44..d2db1be 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -216,38 +216,6 @@ int inet6addr_notifier_call_chain(unsigned long val, void *v);
void inet6_netconf_notify_devconf(struct net *net, int type, int ifindex,
struct ipv6_devconf *devconf);
-/**
- * __in6_dev_get - get inet6_dev pointer from netdevice
- * @dev: network device
- *
- * Caller must hold rcu_read_lock or RTNL, because this function
- * does not take a reference on the inet6_dev.
- */
-static inline struct inet6_dev *__in6_dev_get(const struct net_device *dev)
-{
- return rcu_dereference_rtnl(dev->ip6_ptr);
-}
-
-/**
- * in6_dev_get - get inet6_dev pointer from netdevice
- * @dev: network device
- *
- * This version can be used in any context, and takes a reference
- * on the inet6_dev. Callers must use in6_dev_put() later to
- * release this reference.
- */
-static inline struct inet6_dev *in6_dev_get(const struct net_device *dev)
-{
- struct inet6_dev *idev;
-
- rcu_read_lock();
- idev = rcu_dereference(dev->ip6_ptr);
- if (idev)
- atomic_inc(&idev->refcnt);
- rcu_read_unlock();
- return idev;
-}
-
static inline struct neigh_parms *__in6_dev_nd_parms_get_rcu(const struct net_device *dev)
{
struct inet6_dev *idev = __in6_dev_get(dev);
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index c2626ce..7b5039d 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -174,12 +174,37 @@ static inline bool ipv6_unicast_destination(const struct sk_buff *skb)
int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *));
-static inline int ip6_skb_dst_mtu(struct sk_buff *skb)
+static inline unsigned int ip6_dst_mtu_secure(const struct dst_entry *dst,
+ bool forward)
+{
+ unsigned int mtu;
+ struct inet6_dev *idev;
+ struct net *net = dev_net(dst->dev);
+
+ if (net->ipv6.sysctl.fwd_use_pmtu ||
+ dst_metric_locked(dst, RTAX_MTU))
+ return dst_mtu(dst);
+
+ mtu = IPV6_MIN_MTU;
+ rcu_read_lock();
+ idev = __in6_dev_get(dst->dev);
+ if (idev)
+ mtu = idev->cnf.mtu6;
+ rcu_read_unlock();
+
+ return mtu;
+}
+
+static inline unsigned int ip6_skb_dst_mtu(struct sk_buff *skb)
{
struct ipv6_pinfo *np = skb->sk ? inet6_sk(skb->sk) : NULL;
- return (np && np->pmtudisc >= IPV6_PMTUDISC_PROBE) ?
- skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));
+ if (np && np->pmtudisc >= IPV6_PMTUDISC_PROBE) {
+ return skb_dst(skb)->dev->mtu;
+ } else {
+ bool forward = !!(IP6CB(skb)->flags & IP6SKB_FORWARDED);
+ return ip6_dst_mtu_secure(skb_dst(skb), forward);
+ }
}
static inline bool ip6_sk_accept_pmtu(const struct sock *sk)
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index e600b89..6e4d24b 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -684,6 +684,38 @@ static inline __be32 ip6_flowlabel(const struct ipv6hdr *hdr)
return *(__be32 *)hdr & IPV6_FLOWLABEL_MASK;
}
+/**
+ * __in6_dev_get - get inet6_dev pointer from netdevice
+ * @dev: network device
+ *
+ * Caller must hold rcu_read_lock or RTNL, because this function
+ * does not take a reference on the inet6_dev.
+ */
+static inline struct inet6_dev *__in6_dev_get(const struct net_device *dev)
+{
+ return rcu_dereference_rtnl(dev->ip6_ptr);
+}
+
+/**
+ * in6_dev_get - get inet6_dev pointer from netdevice
+ * @dev: network device
+ *
+ * This version can be used in any context, and takes a reference
+ * on the inet6_dev. Callers must use in6_dev_put() later to
+ * release this reference.
+ */
+static inline struct inet6_dev *in6_dev_get(const struct net_device *dev)
+{
+ struct inet6_dev *idev;
+
+ rcu_read_lock();
+ idev = rcu_dereference(dev->ip6_ptr);
+ if (idev)
+ atomic_inc(&idev->refcnt);
+ rcu_read_unlock();
+ return idev;
+}
+
/*
* Prototypes exported by ipv6
*/
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 0fb2401..05fef12 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -19,6 +19,7 @@ struct netns_sysctl_ipv6 {
struct ctl_table_header *xfrm6_hdr;
#endif
int bindv6only;
+ int fwd_use_pmtu;
int flush_delay;
int ip6_rt_max_size;
int ip6_rt_gc_min_interval;
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index c921d5d..eb14ae93 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -835,6 +835,8 @@ static int __init inet6_init(void)
BUILD_BUG_ON(sizeof(struct inet6_skb_parm) > FIELD_SIZEOF(struct sk_buff, cb));
+ init_net.ipv6.sysctl.fwd_use_pmtu = 1;
+
/* Register the socket-side information for inet6_create. */
for (r = &inetsw6[0]; r < &inetsw6[SOCK_MAX]; ++r)
INIT_LIST_HEAD(r);
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 788c01a..fbda3bf 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -441,7 +441,8 @@ int ip6_forward(struct sk_buff *skb)
}
}
- mtu = dst_mtu(dst);
+ IP6CB(skb)->flags |= IP6SKB_FORWARDED;
+ mtu = ip6_dst_mtu_secure(dst, true);
if (mtu < IPV6_MIN_MTU)
mtu = IPV6_MIN_MTU;
diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
index 107b2f1..ac0e838 100644
--- a/net/ipv6/sysctl_net_ipv6.c
+++ b/net/ipv6/sysctl_net_ipv6.c
@@ -24,6 +24,13 @@ static struct ctl_table ipv6_table_template[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
+ {
+ .procname = "forward_use_pmtu",
+ .data = &init_net.ipv6.sysctl.fwd_use_pmtu,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
{ }
};
@@ -51,6 +58,7 @@ static int __net_init ipv6_sysctl_net_init(struct net *net)
if (!ipv6_table)
goto out;
ipv6_table[0].data = &net->ipv6.sysctl.bindv6only;
+ ipv6_table[1].data = &net->ipv6.sysctl.fwd_use_pmtu;
ipv6_route_table = ipv6_route_sysctl_init(net);
if (!ipv6_route_table)
--
1.8.3.1
--
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