Add server-registry store methods with record-ID validation (step 1)

New IStore methods for a per-server registry (GetServers, GetServerByID,
CreateServer, DeleteServer, GetServerSettings/SaveServerSettings,
GetServerHashes/SaveServerHashes), all additive - existing single-server
methods untouched. Adds util.ValidateRecordID/ValidateInterfaceName and
applies them to every new method taking a server ID, closing a path-
traversal gap before serverID is ever driven by user input (flagged by
a security review pass).

util/util.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"regexp"
 	"strconv"
 	"strings"
 	"text/template"
@@ -165,6 +166,31 @@ func ValidateServerAddresses(cidrs []string) bool {
 	return true
 }
 
+// recordIDPattern restricts identifiers that end up as scribble/jsondb
+// record keys (and therefore as filesystem path components) to a safe,
+// predictable character set - no "/", "..", or other path metacharacters.
+var recordIDPattern = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,64}$`)
+
+// ValidateRecordID validates an identifier before it is used as a jsondb
+// record key (i.e. a filename component under the db directory), to
+// prevent path traversal / arbitrary file writes via a crafted ID.
+func ValidateRecordID(id string) bool {
+	return recordIDPattern.MatchString(id)
+}
+
+// interfaceNamePattern enforces Linux's IFNAMSIZ limit (16 bytes including
+// the trailing NUL, so 15 usable characters) and a safe character set for
+// any string that may later be passed as a network interface name to
+// external tools (wg-quick, systemctl unit names, etc.).
+var interfaceNamePattern = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,15}$`)
+
+// ValidateInterfaceName validates a WireGuard interface name before it is
+// stored or ever used as an argument to exec'd tools such as wg-quick or
+// systemctl, to prevent command/argument injection and invalid interfaces.
+func ValidateInterfaceName(name string) bool {
+	return interfaceNamePattern.MatchString(name)
+}
+
 // ValidateIPAddress to validate the IPv4 and IPv6 address
 func ValidateIPAddress(ip string) bool {
 	if net.ParseIP(ip) == nil {