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Date: Sun, 10 Jan 2010 22:00:34 -0800
From: Stephen Hemminger <shemminger@...tta.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org, linux-api@...r.kernel.org
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@...tta.com>
---
include/linux/in.h | 1 +
include/net/inet_sock.h | 9 +++++++++
net/ipv4/ip_sockglue.c | 14 +++++++++++++-
net/ipv4/tcp_ipv4.c | 2 ++
4 files changed, 25 insertions(+), 1 deletion(-)
--- a/include/linux/in.h 2010-01-10 21:06:42.873122656 -0800
+++ b/include/linux/in.h 2010-01-10 21:06:47.802185618 -0800
@@ -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 */
--- a/include/net/inet_sock.h 2010-01-10 21:06:42.893123288 -0800
+++ b/include/net/inet_sock.h 2010-01-10 21:17:50.262842588 -0800
@@ -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,
--- a/net/ipv4/ip_sockglue.c 2010-01-10 21:06:42.913123212 -0800
+++ b/net/ipv4/ip_sockglue.c 2010-01-10 21:06:47.822184879 -0800
@@ -451,7 +451,8 @@ static int do_ip_setsockopt(struct sock
(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 @@ mc_msf_out:
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
case IP_TRANSPARENT:
val = inet->transparent;
break;
+ case IP_MINTTL:
+ val = inet->min_ttl;
+ break;
default:
release_sock(sk);
return -ENOPROTOOPT;
--- a/net/ipv4/tcp_ipv4.c 2010-01-10 21:06:42.931093698 -0800
+++ b/net/ipv4/tcp_ipv4.c 2010-01-10 21:08:21.537513427 -0800
@@ -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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