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Date: Wed, 24 Jan 2018 10:49:40 +0100
From: Roman Kapl <code@...pl.cz>
To: Xin Long <lucien.xin@...il.com>
Cc: network dev <netdev@...r.kernel.org>,
"David S . Miller" <davem@...emloft.net>,
Jiri Benc <jbenc@...hat.com>,
Pablo Neira Ayuso <pablo@...filter.org>,
Eric Dumazet <edumazet@...gle.com>,
David Ahern <dsahern@...il.com>, Thomas Graf <tgraf@...g.ch>
Subject: Re: [PATCH] net: make sure skb_dst is valid before using
On 01/24/2018 10:16 AM, Xin Long wrote:
> On Wed, Jan 24, 2018 at 6:42 AM, Roman Kapl <code@...pl.cz> wrote:
>> Tunnel devices often use skb_dst(skb)->ops, but ops are not implemented
>> for metadata tunnel destinations. Use skb_valid_dst to check if skb_dst
>> is a real (non-metadata) destination.
>>
>> Such packets can easily be crafted using tc tunnel_key actions or BPF
>> and will crash the tunnels, as observed at least with sit, geneve and
>> vxlan. Some of these tunnels are also intended to be used with metadata
>> destinations, so this represents a loss of functionality.
>>
>> There might be more places with similar patterns, but sometimes it is
>> hard to tell if metadata dst packets can reach them, so this patch is
>> not exhaustive.
> This patch is trying to fix a lot of places, and there may be more.
> But all because of the lack of .update_pmtu or .neigh_lookup.
> (dst_link_failure is safe, btw)
>
> Not sure if it will be better to add .update_pmtu, .neigh_lookup and
> even .redirect for md_dst_ops, but just leave them empty ?
> like fake_dst_ops in br_nf.
That's what I was suggesting in the original mail. However, it might
have slight impact on performance. Also it was not done when metadata
destinations were originally added, was there any good reason?
> Let's see other's opinions.
Exactly.
>
>> Fixes: 52a589d51f10 ("geneve: update skb dst pmtu on tx path")
>> Fixes: a93bf0ff4490 ("vxlan: update skb dst pmtu on tx path")
>> Signed-off-by: Roman Kapl <code@...pl.cz>
>> ---
>> drivers/infiniband/ulp/ipoib/ipoib_cm.c | 3 ++-
>> drivers/net/geneve.c | 5 +++--
>> drivers/net/vxlan.c | 5 +++--
>> drivers/s390/net/qeth_l3_main.c | 7 +++++--
>> include/net/ip6_tunnel.h | 1 +
>> net/ipv4/ip_tunnel.c | 2 +-
>> net/ipv4/ip_vti.c | 3 ++-
>> net/ipv6/sit.c | 7 ++++---
>> 8 files changed, 21 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
>> index 2c13123bfd69..65eacafc898f 100644
>> --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
>> +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
>> @@ -40,6 +40,7 @@
>> #include <linux/moduleparam.h>
>> #include <linux/sched/signal.h>
>> #include <linux/sched/mm.h>
>> +#include <net/dst_metadata.h>
>>
>> #include "ipoib.h"
>>
>> @@ -1456,7 +1457,7 @@ void ipoib_cm_skb_too_long(struct net_device *dev, struct sk_buff *skb,
>> struct ipoib_dev_priv *priv = ipoib_priv(dev);
>> int e = skb_queue_empty(&priv->cm.skb_queue);
>>
>> - if (skb_dst(skb))
>> + if (skb_valid_dst(skb))
>> skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
>>
>> skb_queue_tail(&priv->cm.skb_queue, skb);
>> diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
>> index 195e0d0add8d..2e5d2bc8d851 100644
>> --- a/drivers/net/geneve.c
>> +++ b/drivers/net/geneve.c
>> @@ -19,6 +19,7 @@
>> #include <net/rtnetlink.h>
>> #include <net/geneve.h>
>> #include <net/protocol.h>
>> +#include <net/dst_metadata.h>
>>
>> #define GENEVE_NETDEV_VER "0.6"
>>
>> @@ -825,7 +826,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
>> if (IS_ERR(rt))
>> return PTR_ERR(rt);
>>
>> - if (skb_dst(skb)) {
>> + if (skb_valid_dst(skb)) {
>> int mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr) -
>> GENEVE_BASE_HLEN - info->options_len - 14;
>>
>> @@ -871,7 +872,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
>> if (IS_ERR(dst))
>> return PTR_ERR(dst);
>>
>> - if (skb_dst(skb)) {
>> + if (skb_valid_dst(skb)) {
>> int mtu = dst_mtu(dst) - sizeof(struct ipv6hdr) -
>> GENEVE_BASE_HLEN - info->options_len - 14;
>>
>> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
>> index 82090ae7ced1..b0e96746bc2e 100644
>> --- a/drivers/net/vxlan.c
>> +++ b/drivers/net/vxlan.c
>> @@ -28,6 +28,7 @@
>> #include <net/netns/generic.h>
>> #include <net/tun_proto.h>
>> #include <net/vxlan.h>
>> +#include <net/dst_metadata.h>
>>
>> #if IS_ENABLED(CONFIG_IPV6)
>> #include <net/ip6_tunnel.h>
>> @@ -2155,7 +2156,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
>> }
>>
>> ndst = &rt->dst;
>> - if (skb_dst(skb)) {
>> + if (skb_valid_dst(skb)) {
>> int mtu = dst_mtu(ndst) - VXLAN_HEADROOM;
>>
>> skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
>> @@ -2197,7 +2198,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
>> goto out_unlock;
>> }
>>
>> - if (skb_dst(skb)) {
>> + if (skb_valid_dst(skb)) {
>> int mtu = dst_mtu(ndst) - VXLAN6_HEADROOM;
>>
>> skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
>> diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
>> index b0c888e86cd4..694efab9cccd 100644
>> --- a/drivers/s390/net/qeth_l3_main.c
>> +++ b/drivers/s390/net/qeth_l3_main.c
>> @@ -35,6 +35,7 @@
>> #include <net/ip6_fib.h>
>> #include <net/ip6_checksum.h>
>> #include <net/iucv/af_iucv.h>
>> +#include <net/dst_metadata.h>
>> #include <linux/hashtable.h>
>>
>> #include "qeth_l3.h"
>> @@ -2259,9 +2260,11 @@ static int qeth_l3_get_cast_type(struct sk_buff *skb)
>> struct dst_entry *dst;
>>
>> rcu_read_lock();
>> - dst = skb_dst(skb);
>> - if (dst)
>> + if (skb_valid_dst(skb)) {
>> + dst = skb_dst(skb);
>> n = dst_neigh_lookup_skb(dst, skb);
>> + }
>> +
>> if (n) {
>> int cast_type = n->type;
>>
>> diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h
>> index 236e40ba06bf..1a704dfe5e1a 100644
>> --- a/include/net/ip6_tunnel.h
>> +++ b/include/net/ip6_tunnel.h
>> @@ -148,6 +148,7 @@ struct net *ip6_tnl_get_link_net(const struct net_device *dev);
>> int ip6_tnl_get_iflink(const struct net_device *dev);
>> int ip6_tnl_change_mtu(struct net_device *dev, int new_mtu);
>>
>> +/* Must be called with valid skb_dst */
>> static inline void ip6tunnel_xmit(struct sock *sk, struct sk_buff *skb,
>> struct net_device *dev)
>> {
>> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
>> index 5ddb1cb52bd4..9256e8b9c538 100644
>> --- a/net/ipv4/ip_tunnel.c
>> +++ b/net/ipv4/ip_tunnel.c
>> @@ -520,7 +520,7 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb,
>> else
>> mtu = skb_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
>>
>> - if (skb_dst(skb))
>> + if (skb_valid_dst(skb))
>> skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
>>
>> if (skb->protocol == htons(ETH_P_IP)) {
>> diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
>> index 949f432a5f04..fdb20a95b819 100644
>> --- a/net/ipv4/ip_vti.c
>> +++ b/net/ipv4/ip_vti.c
>> @@ -43,6 +43,7 @@
>> #include <net/xfrm.h>
>> #include <net/net_namespace.h>
>> #include <net/netns/generic.h>
>> +#include <net/dst_metadata.h>
>>
>> static struct rtnl_link_ops vti_link_ops __read_mostly;
>>
>> @@ -172,7 +173,7 @@ static netdev_tx_t vti_xmit(struct sk_buff *skb, struct net_device *dev,
>> int err;
>> int mtu;
>>
>> - if (!dst) {
>> + if (!skb_valid_dst(skb)) {
>> dev->stats.tx_carrier_errors++;
>> goto tx_error_icmp;
>> }
>> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
>> index d7dc23c1b2ca..50a5be98462f 100644
>> --- a/net/ipv6/sit.c
>> +++ b/net/ipv6/sit.c
>> @@ -55,6 +55,7 @@
>> #include <net/dsfield.h>
>> #include <net/net_namespace.h>
>> #include <net/netns/generic.h>
>> +#include <net/dst_metadata.h>
>>
>> /*
>> This version of net/ipv6/sit.c is cloned of net/ipv4/ip_gre.c
>> @@ -837,7 +838,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>> struct neighbour *neigh = NULL;
>> bool do_tx_error = false;
>>
>> - if (skb_dst(skb))
>> + if (skb_valid_dst(skb))
>> neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
>>
>> if (!neigh) {
>> @@ -866,7 +867,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>> struct neighbour *neigh = NULL;
>> bool do_tx_error = false;
>>
>> - if (skb_dst(skb))
>> + if (skb_valid_dst(skb))
>> neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
>>
>> if (!neigh) {
>> @@ -934,7 +935,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>> df = 0;
>> }
>>
>> - if (tunnel->parms.iph.daddr && skb_dst(skb))
>> + if (tunnel->parms.iph.daddr && skb_valid_dst(skb))
>> skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
>>
>> if (skb->len > mtu && !skb_is_gso(skb)) {
>> --
>> 2.15.1
>>
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