| // SPDX-License-Identifier: GPL-2.0 |
| // |
| // Check syncookies. |
| // |
| // Check we are able to rebuild client sack, wscale, ecn and mss options. |
| // IPv4 msstab[4] = { 536, 1300, 1440, 1460 } |
| |
| --ip_version=ipv4 |
| |
| `./defaults.sh |
| sysctl -q net.ipv4.tcp_syncookies=2 |
| ip link set dev tun0 mtu 9000 |
| ` |
| |
| 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 |
| +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 |
| +0 bind(3, ..., ...) = 0 |
| +0 listen(3, 10) = 0 |
| |
| +0 < S 0:0(0) win 32792 <mss 8960,sackOK,TS val 100 ecr 0,nop,wscale 10> |
| +0 > S. 0:0(0) ack 1 <mss 8960,sackOK,TS val 4000 ecr 100,nop,wscale 8> |
| +.01 < . 1:1(0) ack 1 win 1024 <nop,nop,TS val 110 ecr 4000> |
| |
| +0 accept(3, ..., ...) = 4 |
| |
| // Check we properly infer from the final packet the other peer wanted mss >= 1460, wscale 10, sackOK and no ECN. |
| // Note that mss is limited to 1460 - 12 because of IPv4 msstab[] |
| // This is only possible because TCP TS option was used. |
| // Linux uses the SYNACK TS.val 6 low order bits to encode the options. |
| |
| +0 %{ assert tcpi_snd_mss == 1460 - 12, tcpi_snd_mss; \ |
| assert tcpi_snd_wscale == 10, tcpi_snd_wscale; \ |
| assert (tcpi_options & TCPI_OPT_SACK) != 0, tcpi_options; \ |
| assert (tcpi_options & TCPI_OPT_TIMESTAMPS) != 0, tcpi_options; \ |
| assert (tcpi_options & TCPI_OPT_WSCALE) != 0, tcpi_options; \ |
| assert (tcpi_options & TCPI_OPT_ECN) == 0, tcpi_options |
| }% |
