cni: do not exit if the sysctl variable does not exist or can not be set (#4828)

Signed-off-by: zhangzujian <[email protected]>

Author: zhangzujian

cmd/cni/sysctl.go

@@ -5,6 +5,7 @@ package main
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/containernetworking/plugins/pkg/ns"
 	"github.com/containernetworking/plugins/pkg/utils/sysctl"
@@ -19,10 +20,18 @@ func sysctlEnableIPv6(nsPath string) error {
 			name := fmt.Sprintf("net.ipv6.conf.%s.disable_ipv6", conf)
 			value, err := sysctl.Sysctl(name)
 			if err != nil {
+				if os.IsNotExist(err) {
+					// The sysctl variable doesn't exist, so we can't set it
+					continue
+				}
 				return fmt.Errorf("failed to get sysctl variable %s: %w", name, err)
 			}
 			if value != "0" {
 				if _, err = sysctl.Sysctl(name, "0"); err != nil {
+					if os.IsPermission(err) {
+						// We don't have permission to set the sysctl variable, so we can't set it
+						continue
+					}
 					return fmt.Errorf("failed to set sysctl variable %s to 0: %w", name, err)
 				}
 			}