[Bug #20797] Check seconds in UTC offset as well as minutes

spec/ruby/core/time/new_spec.rb

@@ -625,15 +625,15 @@ describe "Time.new with a timezone argument" do
 
         -> {
           Time.new("2020-12-25 00:56:17 +23:59:60")
-        }.should raise_error(ArgumentError, "utc_offset out of range")
+        }.should raise_error(ArgumentError, /utc_offset/)
 
         -> {
           Time.new("2020-12-25 00:56:17 +24:00")
-        }.should raise_error(ArgumentError, "utc_offset out of range")
+        }.should raise_error(ArgumentError, /utc_offset/)
 
         -> {
           Time.new("2020-12-25 00:56:17 +23:61")
-        }.should raise_error(ArgumentError, '"+HH:MM", "-HH:MM", "UTC" or "A".."I","K".."Z" expected for utc_offset: +23:61')
+        }.should raise_error(ArgumentError, /utc_offset/)
       end
 
       it "raises ArgumentError if string has not ascii-compatible encoding" do

test/ruby/test_time.rb

@@ -152,6 +152,18 @@ class TestTime < Test::Unit::TestCase
     assert_raise_with_message(ArgumentError, /can't parse/) {
       Time.new("2020-12-02 00:00:00 ")
     }
+    assert_raise_with_message(ArgumentError, /utc_offset/) {
+      Time.new("2020-12-25 00:00:00 +0960")
+    }
+    assert_raise_with_message(ArgumentError, /utc_offset/) {
+      Time.new("2020-12-25 00:00:00 +09:60")
+    }
+    assert_raise_with_message(ArgumentError, /utc_offset/) {
+      Time.new("2020-12-25 00:00:00 +090060")
+    }
+    assert_raise_with_message(ArgumentError, /utc_offset/) {
+      Time.new("2020-12-25 00:00:00 +09:00:60")
+    }
   end
 
   def test_time_add()

time.c

@@ -2211,6 +2211,7 @@ utc_offset_arg(VALUE arg)
         }
         if (sec) {
             if (!have_2digits(sec)) goto invalid_utc_offset;
+            if (sec[0] > '5') goto invalid_utc_offset;
             n += num_from_2digits(sec);
             ASSUME(min);
         }