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net/dns: fix systemd-resolved detection race at boot

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If systemd-resolved is enabled but not running (or not yet running,
such as early boot) and resolv.conf is old/dangling, we weren't
detecting systemd-resolved.

This moves its ping earlier, which will trigger it to start up and
write its file.

Updates #3362 (likely fixes)
Updates #3531 (likely fixes)

Change-Id: I6392944ac59f600571c43b8f7a677df224f2beed
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-02-10 21:11:18 -08:00
committed by Brad Fitzpatrick
parent 60abeb027b
commit 15599323a1
2 changed files with 60 additions and 15 deletions
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14
net/dns/manager_linux.go
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@@ -77,6 +77,18 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
logf("dns: %v", debug)
}()
// Before we read /etc/resolv.conf (which might be in a broken
// or symlink-dangling state), try to ping the D-Bus service
// for systemd-resolved. If it's active on the machine, this
// will make it start up and write the /etc/resolv.conf file
// before it replies to the ping. (see how systemd's
// src/resolve/resolved.c calls manager_write_resolv_conf
// before the sd_event_loop starts)
resolvedUp := env.dbusPing("org.freedesktop.resolve1", "/org/freedesktop/resolve1") == nil
if resolvedUp {
dbg("resolved-ping", "yes")
}
bs, err := env.fs.ReadFile(resolvConf)
if os.IsNotExist(err) {
dbg("rc", "missing")
@@ -99,7 +111,7 @@ func dnsMode(logf logger.Logf, env newOSConfigEnv) (ret string, err error) {
dbg("resolved", "not-in-use")
return "direct", nil
}
if err := env.dbusPing("org.freedesktop.resolve1", "/org/freedesktop/resolve1"); err != nil {
if !resolvedUp {
dbg("resolved", "no")
return "direct", nil
}