2022-07-15 13:11:54 +02:00
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{ config
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, lib
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, ...
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}: {
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2021-09-30 19:41:08 +02:00
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## System security tweaks
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# sets hidepid=2 on /proc (make process info visible only to owning user)
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# NOTE Was removed on nixpkgs-unstable because it doesn't do anything
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# security.hideProcessInformation = true;
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# Prevent replacing the running kernel w/o reboot
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2022-04-05 11:11:08 +02:00
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security.protectKernelImage = lib.mkDefault true;
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2021-09-30 19:41:08 +02:00
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# tmpfs = /tmp is mounted in ram. Doing so makes temp file management speedy
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# on ssd systems, and volatile! Because it's wiped on reboot.
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boot.tmpOnTmpfs = lib.mkDefault true;
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# If not using tmpfs, which is naturally purged on reboot, we must clean it
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# /tmp ourselves. /tmp should be volatile storage!
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boot.cleanTmpDir = lib.mkDefault (!config.boot.tmpOnTmpfs);
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# Fix a security hole in place for backwards compatibility. See desc in
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# nixpkgs/nixos/modules/system/boot/loader/systemd-boot/systemd-boot.nix
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boot.loader.systemd-boot.editor = false;
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boot.kernel.sysctl = {
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# The Magic SysRq key is a key combo that allows users connected to the
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# system console of a Linux kernel to perform some low-level commands.
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# Disable it, since we don't need it, and is a potential security concern.
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"kernel.sysrq" = 0;
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## TCP hardening
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# Prevent bogus ICMP errors from filling up logs.
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"net.ipv4.icmp_ignore_bogus_error_responses" = 1;
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# Reverse path filtering causes the kernel to do source validation of
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# packets received from all interfaces. This can mitigate IP spoofing.
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"net.ipv4.conf.default.rp_filter" = 1;
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"net.ipv4.conf.all.rp_filter" = 1;
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# Do not accept IP source route packets (we're not a router)
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"net.ipv4.conf.all.accept_source_route" = 0;
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"net.ipv6.conf.all.accept_source_route" = 0;
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# Don't send ICMP redirects (again, we're on a router)
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"net.ipv4.conf.all.send_redirects" = 0;
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"net.ipv4.conf.default.send_redirects" = 0;
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# Refuse ICMP redirects (MITM mitigations)
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"net.ipv4.conf.all.accept_redirects" = 0;
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"net.ipv4.conf.default.accept_redirects" = 0;
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"net.ipv4.conf.all.secure_redirects" = 0;
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"net.ipv4.conf.default.secure_redirects" = 0;
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"net.ipv6.conf.all.accept_redirects" = 0;
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"net.ipv6.conf.default.accept_redirects" = 0;
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# Protects against SYN flood attacks
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"net.ipv4.tcp_syncookies" = 1;
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# Incomplete protection again TIME-WAIT assassination
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"net.ipv4.tcp_rfc1337" = 1;
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2022-04-18 12:26:17 +02:00
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# Log martian packages
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"net.ipv4.conf.all.log_martians" = 1;
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"net.ipv4.conf.default.log_martians" = 1;
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2021-09-30 19:41:08 +02:00
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## TCP optimization
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# TCP Fast Open is a TCP extension that reduces network latency by packing
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# data in the sender’s initial TCP SYN. Setting 3 = enable TCP Fast Open for
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# both incoming and outgoing connections:
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"net.ipv4.tcp_fastopen" = 3;
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# Bufferbloat mitigations + slight improvement in throughput & latency
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"net.ipv4.tcp_congestion_control" = "bbr";
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"net.core.default_qdisc" = "cake";
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};
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boot.kernelModules = [ "tcp_bbr" ];
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# So we don't have to do this later...
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security.acme.acceptTerms = true;
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2021-12-30 11:14:32 +01:00
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2022-04-18 12:26:17 +02:00
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# SSH
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services.openssh = {
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2023-02-02 11:38:23 +01:00
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settings = {
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# Disable ssh password login
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passwordAuthentication = lib.mkDefault false;
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logLevel = "VERBOSE";
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};
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2022-04-18 12:26:17 +02:00
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extraConfig = ''
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AllowAgentForwarding no
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AllowTcpForwarding no
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ClientAliveCountMax 2
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Compression no
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MaxAuthTries 3
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MaxSessions 2
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TCPKeepAlive no
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'';
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};
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2021-09-30 19:41:08 +02:00
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}
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