netfilter: xt_TEE: have cloned packet travel through Xtables too

Since Xtables is now reentrant/nestable, the cloned packet can also go
through Xtables and be subject to rules itself.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

3 files changed, 18 insertions, 24 deletions

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 0abfddec1e26..f09135e1e14f 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -309,7 +309,6 @@ int ip_output(struct sk_buff *skb)
                             ip_finish_output,
                             !(IPCB(skb)->flags & IPSKB_REROUTED));
 }
-EXPORT_SYMBOL_GPL(ip_output);
 
 int ip_queue_xmit(struct sk_buff *skb, int ipfragok)
 {
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d09be7ff8735..c10a38a71a5e 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -176,7 +176,6 @@ int ip6_output(struct sk_buff *skb)
                             ip6_finish_output,
                             !(IP6CB(skb)->flags & IP6SKB_REROUTED));
 }
-EXPORT_SYMBOL_GPL(ip6_output);
 
 /*
  *      xmit an sk_buff (used by TCP)
diff --git a/net/netfilter/xt_TEE.c b/net/netfilter/xt_TEE.c
index b3d730163f12..842e7012eca7 100644
--- a/net/netfilter/xt_TEE.c
+++ b/net/netfilter/xt_TEE.c
@@ -12,6 +12,7 @@
  */
 #include <linux/ip.h>
 #include <linux/module.h>
+#include <linux/percpu.h>
 #include <linux/route.h>
 #include <linux/skbuff.h>
 #include <net/checksum.h>
@@ -32,6 +33,7 @@
 #endif
 
 static const union nf_inet_addr tee_zero_address;
+static DEFINE_PER_CPU(bool, tee_active);
 
 static struct net *pick_net(struct sk_buff *skb)
 {
@@ -91,6 +93,8 @@ tee_tg4(struct sk_buff *skb, const struct xt_target_param *par)
         const struct xt_tee_tginfo *info = par->targinfo;
         struct iphdr *iph;
 
+        if (percpu_read(tee_active))
+                return XT_CONTINUE;
         /*
          * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
          * the original skb, which should continue on its way as if nothing has
@@ -125,24 +129,13 @@ tee_tg4(struct sk_buff *skb, const struct xt_target_param *par)
                 --iph->ttl;
         ip_send_check(iph);
 
-        /*
-         * Xtables is not reentrant currently, so a choice has to be made:
-         * 1. return absolute verdict for the original and let the cloned
-         *    packet travel through the chains
-         * 2. let the original continue travelling and not pass the clone
-         *    to Xtables.
-         * #2 is chosen. Normally, we would use ip_local_out for the clone.
-         * Because iph->check is already correct and we don't pass it to
-         * Xtables anyway, a shortcut to dst_output [forwards to ip_output] can
-         * be taken. %IPSKB_REROUTED needs to be set so that ip_output does not
-         * invoke POSTROUTING on the cloned packet.
-         */
-        IPCB(skb)->flags |= IPSKB_REROUTED;
-        if (tee_tg_route4(skb, info))
-                ip_output(skb);
-        else
+        if (tee_tg_route4(skb, info)) {
+                percpu_write(tee_active, true);
+                ip_local_out(skb);
+                percpu_write(tee_active, false);
+        } else {
                 kfree_skb(skb);
-
+        }
         return XT_CONTINUE;
 }
 
@@ -177,6 +170,8 @@ tee_tg6(struct sk_buff *skb, const struct xt_target_param *par)
 {
         const struct xt_tee_tginfo *info = par->targinfo;
 
+        if (percpu_read(tee_active))
+                return XT_CONTINUE;
         skb = pskb_copy(skb, GFP_ATOMIC);
         if (skb == NULL)
                 return XT_CONTINUE;
@@ -192,12 +187,13 @@ tee_tg6(struct sk_buff *skb, const struct xt_target_param *par)
                 struct ipv6hdr *iph = ipv6_hdr(skb);
                 --iph->hop_limit;
         }
-        IP6CB(skb)->flags |= IP6SKB_REROUTED;
-        if (tee_tg_route6(skb, info))
-                ip6_output(skb);
-        else
+        if (tee_tg_route6(skb, info)) {
+                percpu_write(tee_active, true);
+                ip6_local_out(skb);
+                percpu_write(tee_active, false);
+        } else {
                 kfree_skb(skb);
-
+        }
         return XT_CONTINUE;
 }
 #endif /* WITH_IPV6 */