Harden backup and restore operations

internal/scheduler/cron.go

@@ -7,7 +7,10 @@ import (
 	"time"
 )
 
-type Expression struct{ fields [5]field }
+type Expression struct {
+	fields     [5]field
+	restricted [5]bool
+}
 type field map[int]bool
 
 var bounds = [5][2]int{{0, 59}, {0, 23}, {1, 31}, {1, 12}, {0, 6}}
@@ -24,6 +27,7 @@ func Parse(spec string) (Expression, error) {
 			return Expression{}, fmt.Errorf("cron field %d: %w", i+1, err)
 		}
 		expression.fields[i] = parsed
+		expression.restricted[i] = part != "*"
 	}
 	return expression, nil
 }
@@ -76,11 +80,19 @@ func parseField(value string, min, max int) (field, error) {
 func (e Expression) Matches(t time.Time) bool {
 	values := [5]int{t.Minute(), t.Hour(), t.Day(), int(t.Month()), int(t.Weekday())}
 	for i, value := range values {
+		if i == 2 || i == 4 {
+			continue
+		}
 		if !e.fields[i][value] {
 			return false
 		}
 	}
-	return true
+	dayOfMonth := e.fields[2][values[2]]
+	dayOfWeek := e.fields[4][values[4]]
+	if e.restricted[2] && e.restricted[4] {
+		return dayOfMonth || dayOfWeek
+	}
+	return dayOfMonth && dayOfWeek
 }
 
 func (e Expression) Next(after time.Time) time.Time {