vim-patch:9.1.2023: [security]: Use-after-free in alist_add() with nasty autocmd

Problem:  A BufAdd autocommand may cause alist_add() to use freed
          memory, this is caused by the w_locked variable unset too
          early (henices)
Solution: in trigger_undo_ftplugin() only set w_locked to false, if it
          was false when calling the function.

related: v9.1.0678
closes: vim/vim#19023

9266a2a197

Co-authored-by: Christian Brabandt <cb@256bit.org>

src/nvim/buffer.c

@@ -131,13 +131,14 @@ typedef enum {
 
 static void trigger_undo_ftplugin(buf_T *buf, win_T *win)
 {
+  const bool win_was_locked = win->w_locked;
   window_layout_lock();
   buf->b_locked++;
   win->w_locked = true;
   // b:undo_ftplugin may be set, undo it
   do_cmdline_cmd("if exists('b:undo_ftplugin') | exe b:undo_ftplugin | endif");
   buf->b_locked--;
-  win->w_locked = false;
+  win->w_locked = win_was_locked;
   window_layout_unlock();
 }
 

test/old/testdir/test_arglist.vim

@@ -776,7 +776,6 @@ func Test_crash_arglist_uaf()
   "%argdelete
   new one
   au BufAdd XUAFlocal :bw
-  "call assert_fails(':arglocal XUAFlocal', 'E163:')
   arglocal XUAFlocal
   au! BufAdd
   bw! XUAFlocal
@@ -792,4 +791,15 @@ func Test_crash_arglist_uaf()
   au! BufAdd
 endfunc
 
+" This was using freed memory again
+func Test_crash_arglist_uaf2()
+  new
+  au BufAdd XUAFlocal :bw
+  arglocal XUAFlocal
+  redraw!
+  put ='abc'
+  2#
+  au! BufAdd
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab