wgengine/router: also accept exit code 254 from `ip rule del`.

iproute2 3.16.0-2 from Debian Jessie (oldoldstable) doesn't return
exit code 2 when deleting a non-existent IP rule.

Fixes #434

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/router/router_linux.go

@@ -519,7 +519,7 @@ func (r *linuxRouter) addIPRules() error {
 		return err
 	}
 
-	rg := newRunGroup(0, r.cmd)
+	rg := newRunGroup(nil, r.cmd)
 
 	// NOTE(apenwarr): We leave spaces between each pref number.
 	// This is so the sysadmin can override by inserting rules in
@@ -588,7 +588,10 @@ func (r *linuxRouter) delIPRules() error {
 	// Error codes: 'ip rule' returns error code 2 if the rule is a
 	// duplicate (add) or not found (del). It returns a different code
 	// for syntax errors. This is also true of busybox.
-	rg := newRunGroup(2, r.cmd)
+	//
+	// Some older versions of iproute2 also return error code 254 for
+	// unknown rules during deletion.
+	rg := newRunGroup([]int{2, 254}, r.cmd)
 
 	// When deleting rules, we want to be a bit specific (mention which
 	// table we were routing to) but not *too* specific (fwmarks, etc).

wgengine/router/runner.go

@@ -61,21 +61,31 @@ func (o osCommandRunner) output(args ...string) ([]byte, error) {
 }
 
 type runGroup struct {
-	OkCode int           // an error code that is acceptable, other than 0, if any
+	OkCode []int         // error codes that are acceptable, other than 0, if any
 	Runner commandRunner // the runner that actually runs our commands
 	ErrAcc error         // first error encountered, if any
 }
 
-func newRunGroup(okCode int, runner commandRunner) *runGroup {
+func newRunGroup(okCode []int, runner commandRunner) *runGroup {
 	return &runGroup{
 		OkCode: okCode,
 		Runner: runner,
 	}
 }
 
+func (rg *runGroup) okCode(err error) bool {
+	got := errCode(err)
+	for _, want := range rg.OkCode {
+		if got == want {
+			return true
+		}
+	}
+	return false
+}
+
 func (rg *runGroup) Output(args ...string) []byte {
 	b, err := rg.Runner.output(args...)
-	if rg.ErrAcc == nil && err != nil && errCode(err) != rg.OkCode {
+	if rg.ErrAcc == nil && err != nil && !rg.okCode(err) {
 		rg.ErrAcc = err
 	}
 	return b
@@ -83,7 +93,7 @@ func (rg *runGroup) Output(args ...string) []byte {
 
 func (rg *runGroup) Run(args ...string) {
 	err := rg.Runner.run(args...)
-	if rg.ErrAcc == nil && err != nil && errCode(err) != rg.OkCode {
+	if rg.ErrAcc == nil && err != nil && !rg.okCode(err) {
 		rg.ErrAcc = err
 	}
 }