Validate pod CIDR and service CIDR

src/k8s/pkg/k8sd/features/calico/network.go

@@ -54,7 +54,7 @@ func ApplyNetwork(ctx context.Context, snap snap.Snap, cfg types.Network, annota
 	}
 
 	podIpPools := []map[string]any{}
-	ipv4PodCIDR, ipv6PodCIDR, err := utils.ParseCIDRs(cfg.GetPodCIDR())
+	ipv4PodCIDR, ipv6PodCIDR, err := utils.SplitCIDRStrings(cfg.GetPodCIDR())
 	if err != nil {
 		err = fmt.Errorf("invalid pod cidr: %w", err)
 		return types.FeatureStatus{
@@ -79,7 +79,7 @@ func ApplyNetwork(ctx context.Context, snap snap.Snap, cfg types.Network, annota
 	}
 
 	serviceCIDRs := []string{}
-	ipv4ServiceCIDR, ipv6ServiceCIDR, err := utils.ParseCIDRs(cfg.GetServiceCIDR())
+	ipv4ServiceCIDR, ipv6ServiceCIDR, err := utils.SplitCIDRStrings(cfg.GetServiceCIDR())
 	if err != nil {
 		err = fmt.Errorf("invalid service cidr: %v", err)
 		return types.FeatureStatus{

src/k8s/pkg/k8sd/features/calico/network_test.go

@@ -192,10 +192,10 @@ func TestEnabled(t *testing.T) {
 func validateValues(t *testing.T, values map[string]any, cfg types.Network) {
 	g := NewWithT(t)
 
-	podIPv4CIDR, podIPv6CIDR, err := utils.ParseCIDRs(cfg.GetPodCIDR())
+	podIPv4CIDR, podIPv6CIDR, err := utils.SplitCIDRStrings(cfg.GetPodCIDR())
 	g.Expect(err).ToNot(HaveOccurred())
 
-	svcIPv4CIDR, svcIPv6CIDR, err := utils.ParseCIDRs(cfg.GetServiceCIDR())
+	svcIPv4CIDR, svcIPv6CIDR, err := utils.SplitCIDRStrings(cfg.GetServiceCIDR())
 	g.Expect(err).ToNot(HaveOccurred())
 
 	// calico network

src/k8s/pkg/k8sd/features/cilium/network.go

@@ -44,7 +44,7 @@ func ApplyNetwork(ctx context.Context, snap snap.Snap, cfg types.Network, _ type
 		}, nil
 	}
 
-	ipv4CIDR, ipv6CIDR, err := utils.ParseCIDRs(cfg.GetPodCIDR())
+	ipv4CIDR, ipv6CIDR, err := utils.SplitCIDRStrings(cfg.GetPodCIDR())
 	if err != nil {
 		err = fmt.Errorf("invalid kube-proxy --cluster-cidr value: %v", err)
 		return types.FeatureStatus{

src/k8s/pkg/k8sd/features/cilium/network_test.go

@@ -163,7 +163,7 @@ func validateNetworkValues(t *testing.T, values map[string]any, cfg types.Networ
 	t.Helper()
 	g := NewWithT(t)
 
-	ipv4CIDR, ipv6CIDR, err := utils.ParseCIDRs(cfg.GetPodCIDR())
+	ipv4CIDR, ipv6CIDR, err := utils.SplitCIDRStrings(cfg.GetPodCIDR())
 	g.Expect(err).ToNot(HaveOccurred())
 
 	bpfMount, err := utils.GetMountPath("bpf")

src/k8s/pkg/k8sd/types/cluster_config_validate.go

@@ -6,6 +6,8 @@ import (
 	"net/netip"
 	"net/url"
 	"strings"
+
+	"github.com/canonical/k8s/pkg/utils"
 )
 
 func validateCIDRs(cidrString string) error {
@@ -21,6 +23,65 @@ func validateCIDRs(cidrString string) error {
 	return nil
 }
 
+// validateCIDROverlap checks for overlap and size constraints between pod and service CIDRs.
+// It parses the provided podCIDR and serviceCIDR strings, checks for IPv4 and IPv6 overlaps.
+func validateCIDROverlap(podCIDR string, serviceCIDR string) error {
+	// Parse the CIDRs
+	podIPv4CIDR, podIPv6CIDR, err := utils.SplitCIDRStrings(podCIDR)
+	if err != nil {
+		return fmt.Errorf("failed to parse pod CIDR: %w", err)
+	}
+
+	svcIPv4CIDR, svcIPv6CIDR, err := utils.SplitCIDRStrings(serviceCIDR)
+	if err != nil {
+		return fmt.Errorf("failed to parse service CIDR: %w", err)
+	}
+
+	// Check for IPv4 overlap
+	if podIPv4CIDR != "" && svcIPv4CIDR != "" {
+		if overlap, err := utils.CIDRsOverlap(podIPv4CIDR, svcIPv4CIDR); err != nil {
+			return fmt.Errorf("failed to check for IPv4 overlap: %w", err)
+		} else if overlap {
+			return fmt.Errorf("pod CIDR %q and service CIDR %q overlap", podCIDR, serviceCIDR)
+		}
+	}
+
+	// Check for IPv6 overlap
+	if podIPv6CIDR != "" && svcIPv6CIDR != "" {
+		if overlap, err := utils.CIDRsOverlap(podIPv6CIDR, svcIPv6CIDR); err != nil {
+			return fmt.Errorf("failed to check for IPv6 overlap: %w", err)
+		} else if overlap {
+			return fmt.Errorf("pod CIDR %q and service CIDR %q overlap", podCIDR, serviceCIDR)
+		}
+	}
+
+	return nil
+}
+
+// validateIPv6CIDRSize ensures that the service IPv6 CIDR is not larger than /108.
+// Ref: https://documentation.ubuntu.com/canonical-kubernetes/latest/snap/howto/networking/dualstack/#cidr-size-limitations
+func validateIPv6CIDRSize(serviceCIDR string) error {
+	_, svcIPv6CIDR, err := utils.SplitCIDRStrings(serviceCIDR)
+	if err != nil {
+		return fmt.Errorf("invalid CIDR: %w", err)
+	}
+
+	if svcIPv6CIDR == "" {
+		return nil
+	}
+
+	_, ipv6Net, err := net.ParseCIDR(svcIPv6CIDR)
+	if err != nil {
+		return fmt.Errorf("invalid CIDR: %w", err)
+	}
+
+	if prefixLength, _ := ipv6Net.Mask.Size(); prefixLength < 108 {
+		return fmt.Errorf("service CIDR %q cannot be larger than /108", serviceCIDR)
+	}
+
+	return nil
+}
+
 // Validate that a ClusterConfig does not have conflicting or incompatible options.
 func (c *ClusterConfig) Validate() error {
 	// check: validate that PodCIDR and ServiceCIDR are configured
@@ -31,6 +92,14 @@ func (c *ClusterConfig) Validate() error {
 		return fmt.Errorf("invalid service CIDR: %w", err)
 	}
 
+	if err := validateCIDROverlap(c.Network.GetPodCIDR(), c.Network.GetServiceCIDR()); err != nil {
+		return fmt.Errorf("invalid cidr configuration: %w", err)
+	}
+	// Can't be an else-if, because default values could already be set.
+	if err := validateIPv6CIDRSize(c.Network.GetServiceCIDR()); err != nil {
+		return fmt.Errorf("invalid service CIDR: %w", err)
+	}
+
 	// check: ensure network is enabled if any of ingress, gateway, load-balancer are enabled
 	if !c.Network.GetEnabled() {
 		if c.Gateway.GetEnabled() {

src/k8s/pkg/k8sd/types/cluster_config_validate_test.go

@@ -10,15 +10,18 @@ import (
 
 func TestValidateCIDR(t *testing.T) {
 	for _, tc := range []struct {
-		cidr      string
-		expectErr bool
+		cidr         string
+		expectPodErr bool
+		expectSvcErr bool
 	}{
-		{cidr: "10.1.0.0/16"},
-		{cidr: "2001:0db8::/32"},
-		{cidr: "10.1.0.0/16,2001:0db8::/32"},
-		{cidr: "", expectErr: true},
-		{cidr: "bananas", expectErr: true},
-		{cidr: "fd01::/64,fd02::/64,fd03::/64", expectErr: true},
+		{cidr: "192.168.0.0/16"},
+		{cidr: "2001:0db8::/108"},
+		{cidr: "10.2.0.0/16,2001:0db8::/108"},
+		{cidr: "", expectPodErr: true, expectSvcErr: true},
+		{cidr: "bananas", expectPodErr: true, expectSvcErr: true},
+		{cidr: "fd01::/108,fd02::/108,fd03::/108", expectPodErr: true, expectSvcErr: true},
+		{cidr: "10.1.0.0/32", expectPodErr: true, expectSvcErr: true},
+		{cidr: "2001:0db8::/32", expectSvcErr: true},
 	} {
 		t.Run(tc.cidr, func(t *testing.T) {
 			t.Run("Pod", func(t *testing.T) {
@@ -30,7 +33,7 @@ func TestValidateCIDR(t *testing.T) {
 					},
 				}
 				err := config.Validate()
-				if tc.expectErr {
+				if tc.expectPodErr {
 					g.Expect(err).To(HaveOccurred())
 				} else {
 					g.Expect(err).To(BeNil())
@@ -45,7 +48,7 @@ func TestValidateCIDR(t *testing.T) {
 					},
 				}
 				err := config.Validate()
-				if tc.expectErr {
+				if tc.expectSvcErr {
 					g.Expect(err).To(HaveOccurred())
 				} else {
 					g.Expect(err).To(BeNil())

src/k8s/pkg/utils/cidr.go

@@ -101,8 +101,8 @@ func ParseAddressString(address string, port int64) (string, error) {
 	return util.CanonicalNetworkAddress(address, port), nil
 }
 
-// ParseCIDRs parses the given CIDR string and returns the respective IPv4 and IPv6 CIDRs.
-func ParseCIDRs(CIDRstring string) (string, string, error) {
+// SplitCIDRStrings parses the given CIDR string and returns the respective IPv4 and IPv6 CIDRs.
+func SplitCIDRStrings(CIDRstring string) (string, string, error) {
 	clusterCIDRs := strings.Split(CIDRstring, ",")
 	if v := len(clusterCIDRs); v != 1 && v != 2 {
 		return "", "", fmt.Errorf("invalid CIDR list: %v", clusterCIDRs)
@@ -142,3 +142,25 @@ func ToIPString(ip net.IP) string {
 	}
 	return "[" + ip.String() + "]"
 }
+
+// CIDRsOverlap checks if two given CIDR blocks overlap.
+// It takes two strings representing the CIDR blocks as input and returns a boolean indicating
+// whether they overlap and an error if any of the CIDR blocks are invalid.
+func CIDRsOverlap(cidr1, cidr2 string) (bool, error) {
+	_, ipNet1, err1 := net.ParseCIDR(cidr1)
+	_, ipNet2, err2 := net.ParseCIDR(cidr2)
+
+	if err1 != nil {
+		return false, fmt.Errorf("couldn't parse CIDR block %q: %w", cidr1, err1)
+	}
+
+	if err2 != nil {
+		return false, fmt.Errorf("couldn't parse CIDR block %q: %w", cidr2, err2)
+	}
+
+	if ipNet1.Contains(ipNet2.IP) || ipNet2.Contains(ipNet1.IP) {
+		return true, nil
+	}
+
+	return false, nil
+}

src/k8s/pkg/utils/cidr_test.go

@@ -153,7 +153,7 @@ func TestParseCIDRs(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.input, func(t *testing.T) {
-			ipv4CIDR, ipv6CIDR, err := utils.ParseCIDRs(tc.input)
+			ipv4CIDR, ipv6CIDR, err := utils.SplitCIDRStrings(tc.input)
 			if tc.expectedErr {
 				Expect(err).To(HaveOccurred())
 			} else {