[PATCH] tcp: Generalized TTL Security Mechanism
From: Stephen Hemminger <hidden>
Date: 2010-01-11 06:00:50
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 <redacted> --- 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;