net: add a sysctl to reflect the fwmark on replies

Kernel-originated IP packets that have no user socket associated
with them (e.g., ICMP errors and echo replies, TCP RSTs, etc.)
are emitted with a mark of zero. Add a sysctl to make them have
the same mark as the packet they are replying to.

This allows an administrator that wishes to do so to use
mark-based routing, firewalling, etc. for these replies by
marking the original packets inbound.

Tested using user-mode linux:
 - ICMP/ICMPv6 echo replies and errors.
 - TCP RST packets (IPv4 and IPv6).

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 0 deletions

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index b2704fd0ec80..a32fc4d705da 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -77,6 +77,8 @@ struct netns_ipv4 {
         int sysctl_ip_no_pmtu_disc;
         int sysctl_ip_fwd_use_pmtu;
 
+        int sysctl_fwmark_reflect;
+
         struct ping_group_range ping_group_range;
 
         atomic_t dev_addr_genid;
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 21edaf1f7916..19d3446e59d2 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -30,6 +30,7 @@ struct netns_sysctl_ipv6 {
         int flowlabel_consistency;
         int icmpv6_time;
         int anycast_src_echo_reply;
+        int fwmark_reflect;
 };
 
 struct netns_ipv6 {