tcp: ensure PMTU updates are processed during fastopen

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 <[email protected]>
Reported-by: Neil Spring <[email protected]>
Reviewed-by: Wei Wang <[email protected]>
Acked-by: Yuchung Cheng <[email protected]>
Acked-by: Martin KaFai Lau <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

0 files changed, 0 insertions, 0 deletions