nftables不允许ssh

Question

我的服务器中有如下规则集：

table inet firewall {
    chain INBOUND {
        type filter hook input priority filter; policy drop;
        ct state established,related accept
        ct state invalid drop
        iif "lo" counter packets 0 bytes 0 accept
        ip protocol icmp limit rate 4/second accept
        ip6 nexthdr ipv6-icmp limit rate 4/second accept
        ip protocol igmp limit rate 4/second accept
        tcp dport 22 accept
        log
    }

    chain FORWARD {
        type filter hook forward priority filter; policy drop;
    }

    chain OUTBOUND {
        type filter hook output priority filter; policy drop;
        oif "lo" counter packets 35 bytes 1946 accept
        tcp dport 22 accept
    }
}

我无法从22端口从ssh连接，即使应该打开。如果我输入：

然后，$ nft flush ruleset，22端口允许连接。

我做错什么了？

Answer 1

在我看来，“出站”链中的规则是问题所在。

您有tcp dport 22 accept，但我认为应该是tcp sport 22 accept，因为当SSH数据包从您的服务器出站时，它们将有一个22的源端口，而不是22的目的端口。

Answer 2

将OUTBOUND链更改为：

chain OUTBOUND {
    type filter hook output priority filter; policy drop;

    # Allow traffic from established and related packets, drop invalid
    ct state vmap { established : accept, related : accept, invalid : drop }
    
    # Allow loopback
    oif "lo" accept

    # Accepted ports out (DNS / DHCP / TIME / WEB for package updates / SMTP)
    ct state new udp dport { 53, 67, 123, 547 } accept
    ct state new tcp dport { 53, 80, 443, 587 } accept 

    log prefix "DROP_output: " limit rate 3/second     
}

• 不接受related出站连接阻止sshd响应.

• 总是在每个默认拒绝链的末尾记录丢弃的数据包。当某些东西不起作用时，通常是防火墙问题。