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Date:	Sun, 22 Apr 2012 15:45:47 -0400
From:	Neal Cardwell <>
To:	David Miller <>
Cc:, Eric Dumazet <>,
	Nandita Dukkipati <>,
	Yuchung Cheng <>,,, Tom Herbert <>,
	Neal Cardwell <>
Subject: [PATCH] tcp: fix TCP_MAXSEG for established IPv6 passive sockets

Commit f5fff5d forgot to fix TCP_MAXSEG behavior IPv6 sockets, so IPv6
TCP server sockets that used TCP_MAXSEG would find that the advmss of
child sockets would be incorrect. This commit mirrors the advmss logic
from tcp_v4_syn_recv_sock in tcp_v6_syn_recv_sock. Eventually this
logic should probably be shared between IPv4 and IPv6, but this at
least fixes this issue.

Signed-off-by: Neal Cardwell <>
 net/ipv6/tcp_ipv6.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 86cfe60..98256cf 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1383,6 +1383,10 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 	tcp_sync_mss(newsk, dst_mtu(dst));
 	newtp->advmss = dst_metric_advmss(dst);
+	if (tcp_sk(sk)->rx_opt.user_mss &&
+	    tcp_sk(sk)->rx_opt.user_mss < newtp->advmss)
+		newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;
 	if (tcp_rsk(req)->snt_synack)

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