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authorJason A. Donenfeld <Jason@zx2c4.com>2017-06-24 04:04:38 +0200
committerJason A. Donenfeld <Jason@zx2c4.com>2017-06-24 04:04:38 +0200
commit69c0c344945ba8e9c51491d63b339231fb541818 (patch)
treed80658dc8bec14277a57ac7855bc71acec18cbdb
parentMerge tag 'mlx5-updates-2017-06-20' of git://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux (diff)
downloadlinux-dev-jd/icmp-conntrack.tar.xz
linux-dev-jd/icmp-conntrack.zip
net/icmp: restore source address if packet is NATedjd/icmp-conntrack
The ICMP routines use the source address for two reasons: 1. Rate-limiting ICMP transmissions based on source address, so that one source address cannot provoke a flood of replies. If the source address is wrong, the rate limiting will be incorrectly applied. 2. Choosing the interface and hence new source address of the generated ICMP packet. If the original packet source address is wrong, ICMP replies will be sent from the wrong source address, resulting in either a misdelivery, infoleak, or just general network admin confusion. Most of the time, the icmp_send and icmpv6_send routines can just reach down into the skb's IP header to determine the saddr. However, if icmp_send or icmpv6_send is being called from a network device driver -- there are a few in the tree -- then it's possible that by the time icmp_send or icmpv6_send looks at the packet, the packet's source address has already been transformed by SNAT or MASQUERADE or some other transformation that CONNTRACK knows about. In this case, the packet's source address is most certainly the *wrong* source address to be used for the purpose of ICMP replies. Rather, the source address we want to use for ICMP replies is the original one, from before the transformation occurred. Fortunately, it's very easy to just ask CONNTRACK if it knows about this packet, and if so, how to fix it up. The saddr is the only field in the header we need to fix up, for the purposes of the subsequent processing in the icmp_send and icmpv6_send functions, so we do the lookup very early on, so that the rest of the ICMP machinery can progress as usual. In my tests, this setup works very well. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
-rw-r--r--net/ipv4/icmp.c21
-rw-r--r--net/ipv6/icmp.c21
2 files changed, 42 insertions, 0 deletions
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index c2be26b98b5f..30aa6aa79fd2 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -97,6 +97,10 @@
#include <net/inet_common.h>
#include <net/ip_fib.h>
#include <net/l3mdev.h>
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_nat_core.h>
+#endif
/*
* Build xmit assembly blocks
@@ -586,6 +590,10 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
u32 mark;
struct net *net;
struct sock *sk;
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+ enum ip_conntrack_info ctinfo;
+ struct nf_conn *ct;
+#endif
if (!rt)
goto out;
@@ -604,6 +612,19 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
goto out;
/*
+ * If this function is called after the skb has already been
+ * NAT transformed, the ratelimiting will apply to the wrong
+ * saddr, and the reply will will be marked as coming from the
+ * wrong host. So, we fix it up here in case connection tracking
+ * enables that.
+ */
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+ ct = nf_ct_get(skb_in, &ctinfo);
+ if (ct)
+ iph->saddr = ct->tuplehash[0].tuple.src.u3.ip;
+#endif
+
+ /*
* No replies to physical multicast/broadcast
*/
if (skb_in->pkt_type != PACKET_HOST)
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 8d7b113958b1..ee8a2853121e 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -69,6 +69,10 @@
#include <net/inet_common.h>
#include <net/dsfield.h>
#include <net/l3mdev.h>
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_nat_core.h>
+#endif
#include <linux/uaccess.h>
@@ -422,12 +426,29 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
int len;
int err = 0;
u32 mark = IP6_REPLY_MARK(net, skb->mark);
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+ enum ip_conntrack_info ctinfo;
+ struct nf_conn *ct;
+#endif
if ((u8 *)hdr < skb->head ||
(skb_network_header(skb) + sizeof(*hdr)) > skb_tail_pointer(skb))
return;
/*
+ * If this function is called after the skb has already been
+ * NAT transformed, the ratelimiting will apply to the wrong
+ * saddr, and the reply will will be marked as coming from the
+ * wrong host. So, we fix it up here in case connection tracking
+ * enables that.
+ */
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+ ct = nf_ct_get(skb, &ctinfo);
+ if (ct)
+ hdr->saddr = ct->tuplehash[0].tuple.src.u3.in6;
+#endif
+
+ /*
* Make sure we respect the rules
* i.e. RFC 1885 2.4(e)
* Rule (e.1) is enforced by not using icmp6_send