ipsec: fix per-node-pair-key computation

This commit ensures that

- each time we compute a per-node-pair-key we create an empty slice with
  the correct length first, and then append all the input data instead
  of appending to one of the input slices (`globalKey`) directly.
- the IPs that are used as arguments in `computeNodeIPsecKey` are
  canonical, meaning IPv4 IPs consist of 4 bytes and IPv6 IPs consist of
  16 bytes.

This is necessary to always have the same inputs on all nodes when
computing the per-node-pair-key. Without this IPs might not match on the
byte level, e.g on one node the input is a v6 mapped v4 address (IPv4
address in 16 bytes) and on the other it isn't when used as input to the
hash function. This will generate non-matching keys.

Co-authored-by: Zhichuan Liang <gray.liang@isovalent.com>
Signed-off-by: Robin Gögge <r.goegge@gmail.com>

pkg/datapath/linux/ipsec/ipsec_linux.go

@@ -150,14 +150,26 @@ func getGlobalIPsecKey(ip net.IP) *ipSecKey {
 // pre-shared key. The per-node-pair keys are computed with a SHA256 hash of
 // the global key, source node IP, destination node IP appended together.
 func computeNodeIPsecKey(globalKey, srcNodeIP, dstNodeIP, srcBootID, dstBootID []byte) []byte {
-	input := append(globalKey, srcNodeIP...)
+	inputLen := len(globalKey) + len(srcNodeIP) + len(dstNodeIP) + len(srcBootID) + len(dstBootID)
+	input := make([]byte, 0, inputLen)
+	input = append(input, globalKey...)
+	input = append(input, srcNodeIP...)
 	input = append(input, dstNodeIP...)
-	input = append(input, srcBootID...)
-	input = append(input, dstBootID...)
+	input = append(input, srcBootID[:36]...)
+	input = append(input, dstBootID[:36]...)
 	output := sha256.Sum256(input)
 	return output[:len(globalKey)]
 }
 
+// canonicalIP returns a canonical IPv4 address (4 bytes)
+// in case we were dealing with a v4 mapped V6 address.
+func canonicalIP(ip net.IP) net.IP {
+	if v4 := ip.To4(); v4 != nil {
+		return v4
+	}
+	return ip
+}
+
 // deriveNodeIPsecKey builds a per-node-pair ipSecKey object from the global
 // ipSecKey object.
 func deriveNodeIPsecKey(globalKey *ipSecKey, srcNodeIP, dstNodeIP net.IP, srcBootID, dstBootID string) *ipSecKey {
@@ -167,6 +179,9 @@ func deriveNodeIPsecKey(globalKey *ipSecKey, srcNodeIP, dstNodeIP net.IP, srcBoo
 		ESN:   globalKey.ESN,
 	}
 
+	srcNodeIP = canonicalIP(srcNodeIP)
+	dstNodeIP = canonicalIP(dstNodeIP)
+
 	if globalKey.Aead != nil {
 		nodeKey.Aead = &netlink.XfrmStateAlgo{
 			Name:   globalKey.Aead.Name,