From c0f0e2380e5954f4a52a131bf6b8499838ad1dae Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Sun, 16 Feb 2025 16:06:38 +0100
Subject: [PATCH] patch 9.1.1115: [security]: use-after-free in str_to_reg()

Problem:  [security]: use-after-free in str_to_reg()
          (fizz-is-on-the-way)
Solution: when redirecting the :display command, check that one
          does not output to the register being displayed

Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-63p5-mwg2-787v

Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/register.c                 |  3 ++-
 src/testdir/test_registers.vim | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/register.c b/src/register.c
index 0df05054ca7229..a9630f8ef5db93 100644
--- a/src/register.c
+++ b/src/register.c
@@ -2405,7 +2405,8 @@ ex_display(exarg_T *eap)
 
 #ifdef FEAT_EVAL
 	if (name == MB_TOLOWER(redir_reg)
-		|| (redir_reg == '"' && yb == y_previous))
+		|| (vim_strchr((char_u *)"\"*+", redir_reg) != NULL &&
+		    (yb == y_previous || yb == &y_regs[0])))
 	    continue;	    // do not list register being written to, the
 			    // pointer can be freed
 #endif
diff --git a/src/testdir/test_registers.vim b/src/testdir/test_registers.vim
index 1177c2395d3f09..13127022666e04 100644
--- a/src/testdir/test_registers.vim
+++ b/src/testdir/test_registers.vim
@@ -929,4 +929,24 @@ func Test_register_y_append_reset()
   bwipe!
 endfunc
 
+" This caused use-after-free
+func Test_register_redir_display()
+  " don't touch the clipboard, so only perform this, when the clipboard is not working
+  if has("clipboard_working")
+    throw "Skipped: skip touching the clipboard register!"
+  endif
+  let @"=''
+  redir @+>
+  disp +"
+  redir END
+  call assert_equal("\nType Name Content", getreg('+'))
+  let a = [getreg('1'), getregtype('1')]
+  let @1='register 1'
+  redir @+
+  disp 1
+  redir END
+  call assert_equal("register 1", getreg('1'))
+  call setreg(1, a[0], a[1])
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
