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Restore support for "Override local DNS" (#2438)

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Tailscale allows to override the local DNS settings of a node via
"Override local DNS" [1]. Restore this flag with the same config setting
name `dns.override_local_dns` but disable it by default to align it with
Tailscale's default behaviour.

Tested with Tailscale 1.80.2 and systemd-resolved on Debian 12.

With `dns.override_local_dns: false`:

```
Link 12 (tailscale0)
Current Scopes: DNS
     Protocols: -DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
   DNS Servers: 100.100.100.100
    DNS Domain: tn.example.com ~0.e.1.a.c.5.1.1.a.7.d.f.ip6.arpa [snip]
```

With `dns.override_local_dns: true`:

```
Link 12 (tailscale0)
Current Scopes: DNS
     Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
   DNS Servers: 100.100.100.100
    DNS Domain: tn.example.com ~.
```

[1] https://tailscale.com/kb/1054/dns#override-local-dns

Fixes: #2256
This commit is contained in:
nblock 2025-04-17 17:16:59 +02:00 • committed by GitHub
parent 0fbe392499
commit 1e0516b99d
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GPG key ID: B5690EEEBB952194
12 changed files with 113 additions and 12 deletions
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17
hscontrol/types/config.go
View file

@ -102,6 +102,7 @@ type Config struct {
type DNSConfig struct {
MagicDNS bool `mapstructure:"magic_dns"`
BaseDomain string `mapstructure:"base_domain"`
OverrideLocalDNS bool `mapstructure:"override_local_dns"`
Nameservers Nameservers
SearchDomains []string `mapstructure:"search_domains"`
ExtraRecords []tailcfg.DNSRecord `mapstructure:"extra_records"`
@ -287,6 +288,7 @@ func LoadConfig(path string, isFile bool) error {
viper.SetDefault("dns.magic_dns", true)
viper.SetDefault("dns.base_domain", "")
viper.SetDefault("dns.override_local_dns", true)
viper.SetDefault("dns.nameservers.global", []string{})
viper.SetDefault("dns.nameservers.split", map[string]string{})
viper.SetDefault("dns.search_domains", []string{})
@ -351,9 +353,9 @@ func validateServerConfig() error {
depr.fatalIfNewKeyIsNotUsed("policy.path", "acl_policy_path")
// Move dns_config -> dns
depr.warn("dns_config.override_local_dns")
depr.fatalIfNewKeyIsNotUsed("dns.magic_dns", "dns_config.magic_dns")
depr.fatalIfNewKeyIsNotUsed("dns.base_domain", "dns_config.base_domain")
depr.fatalIfNewKeyIsNotUsed("dns.override_local_dns", "dns_config.override_local_dns")
depr.fatalIfNewKeyIsNotUsed("dns.nameservers.global", "dns_config.nameservers")
depr.fatalIfNewKeyIsNotUsed("dns.nameservers.split", "dns_config.restricted_nameservers")
depr.fatalIfNewKeyIsNotUsed("dns.search_domains", "dns_config.domains")
@ -417,6 +419,12 @@ func validateServerConfig() error {
)
}
if viper.GetBool("dns.override_local_dns") {
if global := viper.GetStringSlice("dns.nameservers.global"); len(global) == 0 {
errorText += "Fatal config error: dns.nameservers.global must be set when dns.override_local_dns is true\n"
}
}
if errorText != "" {
// nolint
return errors.New(strings.TrimSuffix(errorText, "\n"))
@ -616,6 +624,7 @@ func dns() (DNSConfig, error) {
dns.MagicDNS = viper.GetBool("dns.magic_dns")
dns.BaseDomain = viper.GetString("dns.base_domain")
dns.OverrideLocalDNS = viper.GetBool("dns.override_local_dns")
dns.Nameservers.Global = viper.GetStringSlice("dns.nameservers.global")
dns.Nameservers.Split = viper.GetStringMapStringSlice("dns.nameservers.split")
dns.SearchDomains = viper.GetStringSlice("dns.search_domains")
@ -721,7 +730,11 @@ func dnsToTailcfgDNS(dns DNSConfig) *tailcfg.DNSConfig {
cfg.Proxied = dns.MagicDNS
cfg.ExtraRecords = dns.ExtraRecords
cfg.Resolvers = dns.globalResolvers()
if dns.OverrideLocalDNS {
cfg.Resolvers = dns.globalResolvers()
} else {
cfg.FallbackResolvers = dns.globalResolvers()
}
routes := dns.splitResolvers()
cfg.Routes = routes