vim-patch:9.1.0647: [security] use-after-free in tagstack_clear_entry

Problem:  [security] use-after-free in tagstack_clear_entry
          (Suyue Guo )
Solution: Instead of manually calling vim_free() on each of the tagstack
          entries, let's use tagstack_clear_entry(), which will
          also free the stack, but using the VIM_CLEAR macro,
          which prevents a use-after-free by setting those pointers
          to NULL

This addresses CVE-2024-41957

Github advisory:
https://github.com/vim/vim/security/advisories/GHSA-f9cr-gv85-hcr4

8a0bbe7b8a

Co-authored-by: Christian Brabandt <cb@256bit.org>
(cherry picked from commit 6af359ef4c)

src/nvim/tag.c

@@ -3183,7 +3183,7 @@ static int find_extra(char **pp)
 //
 // Free a single entry in a tag stack
 //
-static void tagstack_clear_entry(taggy_T *item)
+void tagstack_clear_entry(taggy_T *item)
 {
   XFREE_CLEAR(item->tagname);
   XFREE_CLEAR(item->user_data);

src/nvim/tag.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "nvim/buffer_defs.h"  // IWYU pragma: keep
 #include "nvim/eval/typval_defs.h"  // IWYU pragma: keep
 #include "nvim/ex_cmds_defs.h"  // IWYU pragma: keep
 #include "nvim/option_defs.h"  // IWYU pragma: keep

src/nvim/window.c

@@ -72,6 +72,7 @@
 #include "nvim/statusline.h"
 #include "nvim/strings.h"
 #include "nvim/syntax.h"
+#include "nvim/tag.h"
 #include "nvim/terminal.h"
 #include "nvim/types_defs.h"
 #include "nvim/ui.h"
@@ -5219,8 +5220,7 @@ void win_free(win_T *wp, tabpage_T *tp)
   xfree(wp->w_lines);
 
   for (int i = 0; i < wp->w_tagstacklen; i++) {
-    xfree(wp->w_tagstack[i].tagname);
-    xfree(wp->w_tagstack[i].user_data);
+    tagstack_clear_entry(&wp->w_tagstack[i]);
   }
 
   xfree(wp->w_localdir);

test/functional/legacy/crash_spec.lua

@@ -1,8 +1,12 @@
+local t = require('test.testutil')
 local n = require('test.functional.testnvim')()
 
 local assert_alive = n.assert_alive
 local clear = n.clear
 local command = n.command
+local eq = t.eq
+local eval = n.eval
+local exec = n.exec
 local feed = n.feed
 
 before_each(clear)
@@ -32,3 +36,18 @@ it('no crash with very long option error message', function()
   pcall(command, 'source test/old/testdir/crash/poc_did_set_langmap')
   assert_alive()
 end)
+
+it('no crash when closing window with tag in loclist', function()
+  exec([[
+    new
+    lexpr ['foo']
+    lopen
+    let g:qf_bufnr = bufnr()
+    lclose
+    call settagstack(1, #{items: [#{tagname: 'foo', from: [g:qf_bufnr, 1, 1, 0]}]})
+  ]])
+  eq(1, eval('bufexists(g:qf_bufnr)'))
+  command('1close')
+  eq(0, eval('bufexists(g:qf_bufnr)'))
+  assert_alive()
+end)

test/old/testdir/test_crash.vim

@@ -190,6 +190,12 @@ func Test_crash1_3()
   call term_sendkeys(buf, args)
   call TermWait(buf, 150)
 
+  let file = 'crash/double_free'
+  let cmn_args = "%s -u NONE -i NONE -n -e -s -S %s -c ':qa!'\<cr>"
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args)
+  call TermWait(buf, 50)
+
   " clean up
   exe buf .. "bw!"
   bw!