Secure array slicing when expanding macro for stack trace (crystal-la…

…ng#11109)
makenowjust · Sep 24, 2021 · cc0b8d1 · cc0b8d1
1 parent ae915ae
commit cc0b8d1
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/src/compiler/crystal/exception.cr b/src/compiler/crystal/exception.cr
@@ -256,8 +256,9 @@ module Crystal
         source, _ = minimize_indentation(source.lines)
         io << Crystal.with_line_numbers(source, line_number, @color)
       else
-        from_index = [0, line_number - MACRO_LINES_TO_SHOW].max
-        source_slice = source.lines[from_index...line_number]
+        to_index = line_number.clamp(0..source.lines.size)
+        from_index = {0, to_index - MACRO_LINES_TO_SHOW}.max
+        source_slice = source.lines[from_index...to_index]
         source_slice, spaces_removed = minimize_indentation(source_slice)
 
         io << Crystal.with_line_numbers(source_slice, line_number, @color, line_number_start = from_index + 1)