pkg/ipam: convert dots to slashes in interface names for sysctl

Since the sysctl key syntax already uses the dot as separator, dots
in interface names that appear in sysctl keys, as is the case for
the net.ipv6.conf.<iface>.* entries, must be replaced by slashes.

Also, print error message to stderr in case sysctl cannot be read
instead of silently hiding the error.

Signed-off-by: David Verbeiren <[email protected]>

pkg/ipam/ipam_linux.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"strings"
 
 	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/plugins/pkg/ip"
@@ -64,12 +65,16 @@ func ConfigureIface(ifName string, res *current.Result) error {
 			// Enabled IPv6 for loopback "lo" and the interface
 			// being configured
 			for _, iface := range [2]string{"lo", ifName} {
-				ipv6SysctlValueName := fmt.Sprintf(DisableIPv6SysctlTemplate, iface)
+				// Cannot have dots in interface name for sysctl, must replace by /
+				ipv6SysctlValueName := fmt.Sprintf(DisableIPv6SysctlTemplate, strings.ReplaceAll(iface, ".", "/"))
 
 				// Read current sysctl value
 				value, err := sysctl.Sysctl(ipv6SysctlValueName)
-				if err != nil || value == "0" {
-					// FIXME: log warning if unable to read sysctl value
+				if err != nil {
+					fmt.Fprintf(os.Stderr, "ipam_linux: failed to read sysctl %q: %v\n", ipv6SysctlValueName, err)
+					continue
+				}
+				if value == "0" {
 					continue
 				}