netdev - [PATCH] TCP: check min TTL on received ICMP packets

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Date:	Thu, 18 Mar 2010 14:27:32 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Pekka Savola <pekkas@...core.fi>
Subject: [PATCH] TCP: check min TTL on received ICMP packets

This adds RFC5082 checks for TTL on received ICMP packets.
It adds some security against spoofed ICMP packets
disrupting GTSM protected sessions.

Signed-off-by: Stephen Hemminger <shemminger@...tta.com>

---
Please apply to 2.6.33 since it basically a "follow correct RFC"
fix to original GTSM patch.

--- a/net/ipv4/tcp_ipv4.c	2010-03-18 11:10:14.396384060 -0700
+++ b/net/ipv4/tcp_ipv4.c	2010-03-18 11:13:09.115759682 -0700
@@ -370,6 +370,11 @@ void tcp_v4_err(struct sk_buff *icmp_skb
 	if (sk->sk_state == TCP_CLOSE)
 		goto out;
 
+	if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) {
+		NET_INC_STATS_BH(net, LINUX_MIB_TCPMINTTLDROP);
+		goto out;
+	}
+
 	icsk = inet_csk(sk);
 	tp = tcp_sk(sk);
 	seq = ntohl(th->seq);
--
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