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

1 files changed, 5 insertions, 0 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 70df40980a8..f4df5f931f3 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -370,6 +370,11 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
         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);