patch 9.0.2112: [security]: overflow in shift_line

Problem:  [security]: overflow in shift_line
Solution: allow a max indent of INT_MAX

[security]: overflow in shift_line

When shifting lines in operator pending mode and using a very large
value, we may overflow the size of integer. Fix this by using a long
variable, testing if the result would be larger than INT_MAX and if so,
indent by INT_MAX value.

Special case: We cannot use long here, since on 32bit architectures (or
on Windows?), it typically cannot take larger values than a plain int,
so we have to use long long count, decide whether the resulting
multiplication of the shiftwidth value * amount is larger than INT_MAX
and if so, we will store INT_MAX as possible larges value in the long
long count variable.

Then we can safely cast it back to int when calling the functions to set
the indent (set_indent() or change_indent()). So this should be safe.

Add a test that when using a huge value in operator pending mode for
shifting, we will shift by INT_MAX

closes: #13535

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_indent.vim

@@ -275,4 +275,15 @@ func Test_formatting_keeps_first_line_indent()
   bwipe!
 endfunc
 
+" Test for indenting with large amount, causes overflow
+func Test_indent_overflow_count()
+  new
+  setl sw=8
+  call setline(1, "abc")
+  norm! V2147483647>
+  " indents by INT_MAX
+  call assert_equal(2147483647, indent(1))
+  close!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab