fs: reject --bwlimit times without a colon or with signed digits

validateHour only checked the length of the hh:mm field and then
parsed the two halves with strconv.Atoi. It never checked the third
character, so "10h20" or "Mon-10.20" were accepted as 10:20, and
since Atoi accepts a sign, "+1:00" and "Mon-10:+5" were accepted
as 01:00 and 10:05.

Require the colon and four digits so these are reported as invalid
time specifications like other malformed times.

fs/bwtimetable.go

@@ -82,9 +82,15 @@ func (x BwTimetable) String() string {
 
 // Basic hour format checking
 func validateHour(HHMM string) error {
-	if len(HHMM) != 5 {
+	if len(HHMM) != 5 || HHMM[2] != ':' {
 		return fmt.Errorf("invalid time specification (hh:mm): %q", HHMM)
 	}
+	// strconv.Atoi accepts a sign, so check for digits explicitly
+	for _, i := range []int{0, 1, 3, 4} {
+		if HHMM[i] < '0' || HHMM[i] > '9' {
+			return fmt.Errorf("invalid time specification (hh:mm): %q", HHMM)
+		}
+	}
 	hh, err := strconv.Atoi(HHMM[0:2])
 	if err != nil {
 		return fmt.Errorf("invalid hour in time specification %q: %v", HHMM, err)

fs/bwtimetable_test.go

@@ -32,6 +32,10 @@ func TestBwTimetableSet(t *testing.T) {
 		{"bad-10:20,666", BwTimetable{}, true, ""},
 		{"Mon-bad,666", BwTimetable{}, true, ""},
 		{"Mon-10:20,bad", BwTimetable{}, true, ""},
+		{"10h20,666", BwTimetable{}, true, ""},
+		{"Mon-10.20,666", BwTimetable{}, true, ""},
+		{"+1:00,666", BwTimetable{}, true, ""},
+		{"Mon-10:+5,666", BwTimetable{}, true, ""},
 		{
 			"0",
 			BwTimetable{