From d218d11133d888f9745802146a50255a4781d37a Mon Sep 17 00:00:00 2001
From: Stephen Hemminger <shemminger@vyatta.com>
Date: Mon, 11 Jan 2010 16:28:01 -0800
Subject: [PATCH] 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>
---
include/linux/in.h | 2 ++
include/net/inet_sock.h | 4 +++-
net/ipv4/ip_sockglue.c | 14 +++++++++++++-
net/ipv4/tcp_ipv4.c | 3 +++
4 files changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/linux/in.h b/include/linux/in.h
index b615649db129e..583c76f9c30fb 100644
--- a/include/linux/in.h
+++ b/include/linux/in.h
@@ -84,6 +84,8 @@ struct in_addr {
#define IP_ORIGDSTADDR 20
#define IP_RECVORIGDSTADDR IP_ORIGDSTADDR
+#define IP_MINTTL 21
+
/* IP_MTU_DISCOVER values */
#define IP_PMTUDISC_DONT 0 /* Never send DF frames */
#define IP_PMTUDISC_WANT 1 /* Use per route hints */
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index bd4c53f75ac02..83fd34437cf1f 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,
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index cafad9baff039..644dc43a55dec 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -451,7 +451,8 @@ static int do_ip_setsockopt(struct sock *sk, int level,
(1<<IP_TTL) | (1<<IP_HDRINCL) |
(1<<IP_MTU_DISCOVER) | (1<<IP_RECVERR) |
(1<<IP_ROUTER_ALERT) | (1<<IP_FREEBIND) |
- (1<<IP_PASSSEC) | (1<<IP_TRANSPARENT))) ||
+ (1<<IP_PASSSEC) | (1<<IP_TRANSPARENT) |
+ (1<<IP_MINTTL))) ||
optname == IP_MULTICAST_TTL ||
optname == IP_MULTICAST_ALL ||
optname == IP_MULTICAST_LOOP ||
@@ -936,6 +937,14 @@ static int do_ip_setsockopt(struct sock *sk, int level,
inet->transparent = !!val;
break;
+ case IP_MINTTL:
+ if (optlen < 1)
+ goto e_inval;
+ if (val < 0 || val > 255)
+ goto e_inval;
+ inet->min_ttl = val;
+ break;
+
default:
err = -ENOPROTOOPT;
break;
@@ -1198,6 +1207,9 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
case IP_TRANSPARENT:
val = inet->transparent;
break;
+ case IP_MINTTL:
+ val = inet->min_ttl;
+ break;
default:
release_sock(sk);
return -ENOPROTOOPT;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 65b8ebfd078a3..382f667238ece 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1649,6 +1649,9 @@ int tcp_v4_rcv(struct sk_buff *skb)
if (!sk)
goto no_tcp_socket;
+ if (iph->ttl < inet_sk(sk)->min_ttl)
+ goto discard_and_relse;
+
process:
if (sk->sk_state == TCP_TIME_WAIT)
goto do_time_wait;
--
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