From: Jakub Kicinski kuba@kernel.org
[ Upstream commit ed0c99dc0f499ff8b6e75b5ae6092ab42be1ad39 ]
tp->rx_opt.mss_clamp is not populated, yet, during TFO send so we rise it to the local MSS. tp->mss_cache is not updated, however:
tcp_v6_connect(): tp->rx_opt.mss_clamp = IPV6_MIN_MTU - headers; tcp_connect(): tcp_connect_init(): tp->mss_cache = min(mtu, tp->rx_opt.mss_clamp) tcp_send_syn_data(): tp->rx_opt.mss_clamp = tp->advmss
After recent fixes to ICMPv6 PTB handling we started dropping PMTU updates higher than tp->mss_cache. Because of the stale tp->mss_cache value PMTU updates during TFO are always dropped.
Thanks to Wei for helping zero in on the problem and the fix!
Fixes: c7bb4b89033b ("ipv6: tcp: drop silly ICMPv6 packet too big messages") Reported-by: Andre Nash alnash@fb.com Reported-by: Neil Spring ntspring@fb.com Reviewed-by: Wei Wang weiwan@google.com Acked-by: Yuchung Cheng ycheng@google.com Acked-by: Martin KaFai Lau kafai@fb.com Signed-off-by: Jakub Kicinski kuba@kernel.org Reviewed-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/r/20220321165957.1769954-1-kuba@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_output.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 0492f6942778..369752f5f676 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3734,6 +3734,7 @@ static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb) */ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) { + struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct tcp_fastopen_request *fo = tp->fastopen_req; int space, err = 0; @@ -3748,8 +3749,10 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) * private TCP options. The cost is reduced data space in SYN :( */ tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp); + /* Sync mss_cache after updating the mss_clamp */ + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
- space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) - + space = __tcp_mtu_to_mss(sk, icsk->icsk_pmtu_cookie) - MAX_TCP_OPTION_SPACE;
space = min_t(size_t, space, fo->size);