tcp: Generalized TTL Security Mechanism

This patch adds the kernel portions needed to implement
RFC 5082 Generalized TTL Security Mechanism (GTSM).
It is a lightweight security measure against forged
packets causing DoS attacks (for BGP). 

This is already implemented the same way in BSD kernels.
For the necessary Quagga patch 
  http://www.gossamer-threads.com/lists/quagga/dev/17389

Description from Cisco
  http://www.cisco.com/en/US/docs/ios/12_3t/12_3t7/feature/guide/gt_btsh.html

It does add one byte to each socket structure, but I did
a little rearrangement to reuse a hole (on 64 bit), but it
does grow the structure on 32 bit

This should be documented on ip(4) man page and the Glibc in.h
file also needs update.  IPV6_MINHOPLIMIT should also be added
(although BSD doesn't support that).  

Only TCP is supported, but could also be added to UDP, DCCP, SCTP
if desired.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index bd4c53f75ac0..83fd34437cf1 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -122,10 +122,12 @@ struct inet_sock {
         __be32                  inet_saddr;
         __s16                   uc_ttl;
         __u16                   cmsg_flags;
-        struct ip_options       *opt;
         __be16                  inet_sport;
         __u16                   inet_id;
+
+        struct ip_options       *opt;
         __u8                    tos;
+        __u8                    min_ttl;
         __u8                    mc_ttl;
         __u8                    pmtudisc;
         __u8                    recverr:1,