mirror of
https://github.com/netbirdio/netbird.git
synced 2026-10-03 12:09:09 +02:00
Brad Ison
f400f4bee8
Direct-upstream targets are dialled on the proxy host's network stack, outside the embedded client's LAN blocking. A proxy that serves untrusted accounts lets them reach the host's loopback, its LAN or cluster, and the cloud metadata service through such a target. NB_PROXY_DIRECT_UPSTREAM_BLOCK_PRIVATE adds a dialer control that refuses addresses that are not globally reachable. It checks each socket's resolved address just before connect, so hostnames and DNS rebinding are covered, and IPv4 embedded in IPv6 addresses is checked as IPv4. Refused dials are served as a 502. The setting defaults to off for private and self-hosted proxies; an unparsable value turns it on.
91 lines
3.4 KiB
Go
91 lines
3.4 KiB
Go
package roundtrip
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import (
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"context"
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"errors"
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"net/netip"
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"syscall"
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)
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// ErrDirectUpstreamBlocked is returned when a direct-upstream dial targets
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// an address that is not globally reachable while
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// NB_PROXY_DIRECT_UPSTREAM_BLOCK_PRIVATE is set.
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var ErrDirectUpstreamBlocked = errors.New("direct upstream address is not allowed")
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// blockedUpstreamPrefixes are the ranges that reach the proxy host, its
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// cluster or its cloud provider rather than the public internet. NAT64
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// and 6to4 addresses are matched by the IPv4 address they embed.
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var blockedUpstreamPrefixes = []netip.Prefix{
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// IPv4
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netip.MustParsePrefix("0.0.0.0/8"), // "this network", including 0.0.0.0
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netip.MustParsePrefix("10.0.0.0/8"), // RFC1918
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netip.MustParsePrefix("100.64.0.0/10"), // CGNAT
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netip.MustParsePrefix("127.0.0.0/8"), // loopback
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netip.MustParsePrefix("169.254.0.0/16"), // link-local, cloud metadata services
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netip.MustParsePrefix("172.16.0.0/12"), // RFC1918
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netip.MustParsePrefix("192.0.0.0/24"), // IETF protocol assignments
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netip.MustParsePrefix("192.0.2.0/24"), // documentation
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netip.MustParsePrefix("192.88.99.0/24"), // 6to4 relay anycast (deprecated)
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netip.MustParsePrefix("192.168.0.0/16"), // RFC1918
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netip.MustParsePrefix("198.18.0.0/15"), // benchmarking
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netip.MustParsePrefix("198.51.100.0/24"), // documentation
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netip.MustParsePrefix("203.0.113.0/24"), // documentation
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netip.MustParsePrefix("224.0.0.0/4"), // multicast
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netip.MustParsePrefix("240.0.0.0/4"), // reserved, including broadcast
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// IPv6
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netip.MustParsePrefix("::/96"), // unspecified, loopback, IPv4-compatible
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netip.MustParsePrefix("64:ff9b:1::/48"), // local-use NAT64
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netip.MustParsePrefix("100::/64"), // discard-only
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netip.MustParsePrefix("2001::/32"), // Teredo
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netip.MustParsePrefix("2001:2::/48"), // benchmarking
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netip.MustParsePrefix("2001:db8::/32"), // documentation
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netip.MustParsePrefix("3fff::/20"), // documentation
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netip.MustParsePrefix("5f00::/16"), // SRv6 SIDs
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netip.MustParsePrefix("fc00::/7"), // unique local, including AWS IMDS fd00:ec2::254
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netip.MustParsePrefix("fe80::/10"), // link-local
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netip.MustParsePrefix("fec0::/10"), // site-local (deprecated)
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netip.MustParsePrefix("ff00::/8"), // multicast
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}
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var (
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nat64Prefix = netip.MustParsePrefix("64:ff9b::/96")
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sixToFour = netip.MustParsePrefix("2002::/16")
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)
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// isBlockedUpstreamAddr reports whether a guarded direct-upstream dial
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// must refuse addr.
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func isBlockedUpstreamAddr(addr netip.Addr) bool {
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addr = addr.Unmap().WithZone("")
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if !addr.IsValid() {
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return true
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}
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if nat64Prefix.Contains(addr) {
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b := addr.As16()
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return isBlockedUpstreamAddr(netip.AddrFrom4([4]byte(b[12:16])))
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}
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if sixToFour.Contains(addr) {
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b := addr.As16()
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return isBlockedUpstreamAddr(netip.AddrFrom4([4]byte(b[2:6])))
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}
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for _, p := range blockedUpstreamPrefixes {
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if p.Contains(addr) {
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return true
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}
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}
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return false
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}
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// guardUpstreamDial is a net.Dialer ControlContext that refuses blocked
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// addresses. It sees the resolved address of each socket just before
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// connect, so DNS rebinding cannot swap the target after the check.
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func guardUpstreamDial(_ context.Context, _, address string, _ syscall.RawConn) error {
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ap, err := netip.ParseAddrPort(address)
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if err != nil || isBlockedUpstreamAddr(ap.Addr()) {
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return ErrDirectUpstreamBlocked
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}
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return nil
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}
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