kernel/linux.git/include/net/tcp.h, branch v4.12.9

net: Update TCP congestion control documentation

2017-06-05T14:53:24+00:00

Update tcp.txt to fix mandatory congestion control ops and default CCA selection. Also, fix comment in tcp.h for undo_cwnd. Signed-off-by: Anmol Sarma Signed-off-by: David S. Miller

tcp: make congestion control optionally skip slow start after idle

2017-05-08T18:37:07+00:00

Congestion control modules that want full control over congestion control behavior do not want the cwnd modifications controlled by the sysctl_tcp_slow_start_after_idle code path. So skip those code paths for CC modules that use the cong_control() API. As an example, those cwnd effects are not desired for the BBR congestion control algorithm. Fixes: c0402760f565 ("tcp: new CC hook to set sending rate with rate_sample in any CA state") Signed-off-by: Wei Wang Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller

tcp: randomize timestamps on syncookies

2017-05-05T16:00:11+00:00

Whole point of randomization was to hide server uptime, but an attacker can simply start a syn flood and TCP generates 'old style' timestamps, directly revealing server jiffies value. Also, TSval sent by the server to a particular remote address vary depending on syncookies being sent or not, potentially triggering PAWS drops for innocent clients. Lets implement proper randomization, including for SYNcookies. Also we do not need to export sysctl_tcp_timestamps, since it is not used from a module. In v2, I added Florian feedback and contribution, adding tsoff to tcp_get_cookie_sock(). v3 removed one unused variable in tcp_v4_connect() as Florian spotted. Fixes: 95a22caee396c ("tcp: randomize tcp timestamp offsets for each connection") Signed-off-by: Eric Dumazet Reviewed-by: Florian Westphal Tested-by: Florian Westphal Cc: Yuchung Cheng Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_rack_advance()

2017-04-26T18:44:38+00:00

No longer needed, since tp->tcp_mstamp holds the information. This is needed to remove sack_state.ack_time in a following patch. Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Acked-by: Neal Cardwell Signed-off-by: David S. Miller

tcp: do not pass timestamp to tcp_rate_gen()

2017-04-26T18:44:38+00:00

tcp: do not pass timestamp to tcp_rack_mark_lost()

2017-04-26T18:44:37+00:00

This is no longer used, since tcp_rack_detect_loss() takes the timestamp from tp->tcp_mstamp Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Acked-by: Neal Cardwell Signed-off-by: David S. Miller

net/tcp_fastopen: Add snmp counter for blackhole detection

2017-04-24T18:27:17+00:00

This counter records the number of times the firewall blackhole issue is detected and active TFO is disabled. Signed-off-by: Wei Wang Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller

net/tcp_fastopen: Disable active side TFO in certain scenarios

2017-04-24T18:27:17+00:00

Middlebox firewall issues can potentially cause server's data being blackholed after a successful 3WHS using TFO. Following are the related reports from Apple: https://www.nanog.org/sites/default/files/Paasch_Network_Support.pdf Slide 31 identifies an issue where the client ACK to the server's data sent during a TFO'd handshake is dropped. C ---> syn-data ---> S C <--- syn/ack ----- S C (accept & write) C <---- data ------- S C ----- ACK -> X S [retry and timeout] https://www.ietf.org/proceedings/94/slides/slides-94-tcpm-13.pdf Slide 5 shows a similar situation that the server's data gets dropped after 3WHS. C ---- syn-data ---> S C <--- syn/ack ----- S C ---- ack --------> S S (accept & write) C? X <- data ------ S [retry and timeout] This is the worst failure b/c the client can not detect such behavior to mitigate the situation (such as disabling TFO). Failing to proceed, the application (e.g., SSL library) may simply timeout and retry with TFO again, and the process repeats indefinitely. The proposed solution is to disable active TFO globally under the following circumstances: 1. client side TFO socket detects out of order FIN 2. client side TFO socket receives out of order RST We disable active side TFO globally for 1hr at first. Then if it happens again, we disable it for 2h, then 4h, 8h, ... And we reset the timeout to 1hr if a client side TFO sockets not opened on loopback has successfully received data segs from server. And we examine this condition during close(). The rational behind it is that when such firewall issue happens, application running on the client should eventually close the socket as it is not able to get the data it is expecting. Or application running on the server should close the socket as it is not able to receive any response from client. In both cases, out of order FIN or RST will get received on the client given that the firewall will not block them as no data are in those frames. And we want to disable active TFO globally as it helps if the middle box is very close to the client and most of the connections are likely to fail. Also, add a debug sysctl: tcp_fastopen_blackhole_detect_timeout_sec: the initial timeout to use when firewall blackhole issue happens. This can be set and read. When setting it to 0, it means to disable the active disable logic. Signed-off-by: Wei Wang Acked-by: Yuchung Cheng Acked-by: Neal Cardwell Signed-off-by: David S. Miller

net: tcp: Define the TCP_MAX_WSCALE instead of literal number 14

2017-04-05T14:50:32+00:00

Define one new macro TCP_MAX_WSCALE instead of literal number '14', and use U16_MAX instead of 65535 as the max value of TCP window. There is another minor change, use rounddown(space, mss) instead of (space / mss) * mss; Signed-off-by: Gao Feng Signed-off-by: David S. Miller

tcp: sysctl: Fix a race to avoid unexpected 0 window from space

2017-03-24T20:29:16+00:00

Because sysctl_tcp_adv_win_scale could be changed any time, so there is one race in tcp_win_from_space. For example, 1.sysctl_tcp_adv_win_scale<=0 (sysctl_tcp_adv_win_scale is negative now) 2.space>>(-sysctl_tcp_adv_win_scale) (sysctl_tcp_adv_win_scale is postive now) As a result, tcp_win_from_space returns 0. It is unexpected. Certainly if the compiler put the sysctl_tcp_adv_win_scale into one register firstly, then use the register directly, it would be ok. But we could not depend on the compiler behavior. Signed-off-by: Gao Feng Signed-off-by: David S. Miller