| Message ID | 20220316235908.1246615-1-kuba@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [RFC,net] tcp: ensure PMTU updates are processed during fastopen | expand |
On Wed, Mar 16, 2022 at 4:59 PM Jakub Kicinski <kuba@kernel.org> wrote: > > 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> Thanks for the fix. > Signed-off-by: Jakub Kicinski <kuba@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 5079832af5c1..257780f93305 100644 > --- a/net/ipv4/tcp_output.c > +++ b/net/ipv4/tcp_output.c > @@ -3719,6 +3719,7 @@ 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; > @@ -3733,8 +3734,10 @@ 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); > -- > 2.34.1 >
On Wed, Mar 16, 2022 at 04:59:08PM -0700, Jakub Kicinski wrote: > 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> > Signed-off-by: Jakub Kicinski <kuba@kernel.org> Acked-by: Martin KaFai Lau <kafai@fb.com>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 5079832af5c1..257780f93305 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3719,6 +3719,7 @@ 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; @@ -3733,8 +3734,10 @@ 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);
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> Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- net/ipv4/tcp_output.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)