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net/dns: support GetBaseConfig on Darwin OSS tailscaled (#13351)

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Updates tailscale/tailscale#177

It appears that the OSS distribution of `tailscaled` is currently unable to get the current system base DNS configuration, as GetBaseConfig() in manager_darwin.go is unimplemented. This PR adds a basic implementation that reads the current values in `/etc/resolv.conf`, to at least unblock DNS resolution via Quad100 if `--accept-dns` is enabled.

Signed-off-by: Andrea Gottardo <andrea@gottardo.me>
This commit is contained in:
Andrea Gottardo 2024-09-04 10:31:58 -07:00 committed by GitHub
parent 1fc4268aea
commit 0112da6070
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1 changed files with 31 additions and 1 deletions
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32
net/dns/manager_darwin.go
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@ -10,6 +10,8 @@
"go4.org/mem"
"tailscale.com/control/controlknobs"
"tailscale.com/health"
"tailscale.com/net/dns/resolvconffile"
"tailscale.com/net/tsaddr"
"tailscale.com/types/logger"
"tailscale.com/util/mak"
)
@ -83,8 +85,36 @@ func (c *darwinConfigurator) SetDNS(cfg OSConfig) error {
return c.removeResolverFiles(func(domain string) bool { return !keep[domain] })
}
// GetBaseConfig returns the current OS DNS configuration, extracting it from /etc/resolv.conf.
// We should really be using the SystemConfiguration framework to get this information, as this
// is not a stable public API, and is provided mostly as a compatibility effort with Unix
// tools. Apple might break this in the future. But honestly, parsing the output of `scutil --dns`
// is *even more* likely to break in the future.
func (c *darwinConfigurator) GetBaseConfig() (OSConfig, error) {
return OSConfig{}, ErrGetBaseConfigNotSupported
cfg := OSConfig{}
resolvConf, err := resolvconffile.ParseFile("/etc/resolv.conf")
if err != nil {
c.logf("failed to parse /etc/resolv.conf: %v", err)
return cfg, ErrGetBaseConfigNotSupported
}
for _, ns := range resolvConf.Nameservers {
if ns == tsaddr.TailscaleServiceIP() || ns == tsaddr.TailscaleServiceIPv6() {
// If we find Quad100 in /etc/resolv.conf, we should ignore it
c.logf("ignoring 100.100.100.100 resolver IP found in /etc/resolv.conf")
continue
}
cfg.Nameservers = append(cfg.Nameservers, ns)
}
cfg.SearchDomains = resolvConf.SearchDomains
if len(cfg.Nameservers) == 0 {
// Log a warning in case we couldn't find any nameservers in /etc/resolv.conf.
c.logf("no nameservers found in /etc/resolv.conf, DNS resolution might fail")
}
return cfg, nil
}
const macResolverFileHeader = "# Added by tailscaled\n"