Reject negative manual ban durations

admin.go

@@ -880,17 +880,30 @@ func (b *Barnard) addManualBan(text string) {
 		b.AddOutputLine("Admin: ban address must be CIDR, for example 192.0.2.1/32")
 		return
 	}
-	minutes, err := strconv.Atoi(parts[1])
+	duration, err := manualBanDuration(parts[1])
 	if err != nil {
-		b.AddOutputLine("Admin: ban minutes must be a number")
+		b.AddOutputLine("Admin: " + err.Error())
 		return
 	}
 	reason := strings.Join(parts[2:], " ")
-	b.adminBanList.Add(ip, network.Mask, reason, time.Duration(minutes)*time.Minute)
+	b.adminBanList.Add(ip, network.Mask, reason, duration)
 	b.Client.Send(b.adminBanList)
 	b.AddOutputLine("Admin: manual ban sent")
 }
 
+// manualBanDuration validates user input before it reaches the unsigned
+// protocol duration field.
+func manualBanDuration(text string) (time.Duration, error) {
+	minutes, err := strconv.Atoi(text)
+	if err != nil {
+		return 0, fmt.Errorf("ban minutes must be a number")
+	}
+	if minutes < 0 {
+		return 0, fmt.Errorf("ban minutes must not be negative")
+	}
+	return time.Duration(minutes) * time.Minute, nil
+}
+
 func (b *Barnard) unbanIndex(index int) {
 	if index < 0 || index >= len(b.adminBanList) {
 		b.AddOutputLine("Admin: ban index out of range")