Fix ip-range for classless subnet masks

The `LastIPInSubnet` function worked only for classful subnet
masks (e.g. /8, /16, /24). For non standard subnet masks this
returned the wrong ip address.

This works now for all subnet mask. A unit test is added to
ensure this.

Signed-off-by: Paul Holzinger <paul.holzinger@web.de>

1 files changed, 7 insertions, 7 deletions

diff --git a/libpod/network/subnet.go b/libpod/network/subnet.go
index 90f0cdfce..120038e57 100644
--- a/libpod/network/subnet.go
+++ b/libpod/network/subnet.go
@@ -54,14 +54,10 @@ func LastIPInSubnet(addr *net.IPNet) (net.IP, error) { //nolint:interfacer
 
 	ones, bits := cidr.Mask.Size()
 	if ones == bits {
-		return FirstIPInSubnet(cidr)
+		return cidr.IP, nil
 	}
-	hostStart := ones / 8
-	// Handle the first host byte
-	cidr.IP[hostStart] |= 0xff & cidr.Mask[hostStart]
-	// Fill the rest with ones
-	for i := hostStart; i < len(cidr.IP); i++ {
-		cidr.IP[i] = 0xff
+	for i := range cidr.IP {
+		cidr.IP[i] = cidr.IP[i] | ^cidr.Mask[i]
 	}
 	return cidr.IP, nil
 }
@@ -73,6 +69,10 @@ func FirstIPInSubnet(addr *net.IPNet) (net.IP, error) { //nolint:interfacer
 	if err != nil {
 		return nil, err
 	}
+	ones, bits := cidr.Mask.Size()
+	if ones == bits {
+		return cidr.IP, nil
+	}
 	cidr.IP[len(cidr.IP)-1]++
 	return cidr.IP, nil
 }