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authorHannes Frederic Sowa <hannes@stressinduktion.org>2014-01-09 09:01:15 (GMT)
committerDavid S. Miller <davem@davemloft.net>2014-01-13 19:22:54 (GMT)
commitf87c10a8aa1e82498c42d0335524d6ae7cf5a52b (patch)
tree85117fae4f0f25831d4232155b47f3f6553faf27 /include/net/ip.h
parent6c76a07a711165a31332aa619215f961b115071d (diff)
downloadlinux-f87c10a8aa1e82498c42d0335524d6ae7cf5a52b.tar.xz
ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing
While forwarding we should not use the protocol path mtu to calculate the mtu for a forwarded packet but instead use the interface mtu. We mark forwarded skbs in ip_forward with IPSKB_FORWARDED, which was introduced for multicast forwarding. But as it does not conflict with our usage in unicast code path it is perfect for reuse. I moved the functions ip_sk_accept_pmtu, ip_sk_use_pmtu and ip_skb_dst_mtu along with the new ip_dst_mtu_maybe_forward to net/ip.h to fix circular dependencies because of IPSKB_FORWARDED. Because someone might have written a software which does probe destinations manually and expects the kernel to honour those path mtus I introduced a new per-namespace "ip_forward_use_pmtu" knob so someone can disable this new behaviour. We also still use mtus which are locked on a route for forwarding. The reason for this change is, that path mtus information can be injected into the kernel via e.g. icmp_err protocol handler without verification of local sockets. As such, this could cause the IPv4 forwarding path to wrongfully emit fragmentation needed notifications or start to fragment packets along a path. Tunnel and ipsec output paths clear IPCB again, thus IPSKB_FORWARDED won't be set and further fragmentation logic will use the path mtu to determine the fragmentation size. They also recheck packet size with help of path mtu discovery and report appropriate errors. Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: David Miller <davem@davemloft.net> Cc: John Heffner <johnwheffner@gmail.com> Cc: Steffen Klassert <steffen.klassert@secunet.com> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/ip.h')
-rw-r--r--include/net/ip.h33
1 files changed, 33 insertions, 0 deletions
diff --git a/include/net/ip.h b/include/net/ip.h
index 5356644..0dab95c 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -263,6 +263,39 @@ int ip_dont_fragment(struct sock *sk, struct dst_entry *dst)
!(dst_metric_locked(dst, RTAX_MTU)));
}
+static inline bool ip_sk_accept_pmtu(const struct sock *sk)
+{
+ return inet_sk(sk)->pmtudisc != IP_PMTUDISC_INTERFACE;
+}
+
+static inline bool ip_sk_use_pmtu(const struct sock *sk)
+{
+ return inet_sk(sk)->pmtudisc < IP_PMTUDISC_PROBE;
+}
+
+static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
+ bool forwarding)
+{
+ struct net *net = dev_net(dst->dev);
+
+ if (net->ipv4.sysctl_ip_fwd_use_pmtu ||
+ dst_metric_locked(dst, RTAX_MTU) ||
+ !forwarding)
+ return dst_mtu(dst);
+
+ return min(dst->dev->mtu, IP_MAX_MTU);
+}
+
+static inline unsigned int ip_skb_dst_mtu(const struct sk_buff *skb)
+{
+ if (!skb->sk || ip_sk_use_pmtu(skb->sk)) {
+ bool forwarding = IPCB(skb)->flags & IPSKB_FORWARDED;
+ return ip_dst_mtu_maybe_forward(skb_dst(skb), forwarding);
+ } else {
+ return min(skb_dst(skb)->dev->mtu, IP_MAX_MTU);
+ }
+}
+
void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more);
static inline void ip_select_ident(struct sk_buff *skb, struct dst_entry *dst, struct sock *sk)