From eec0c2b3a4cfab93dd8d4adaa60638d47a2bbc8a Mon Sep 17 00:00:00 2001
From: Christian Brabandt <cb@256bit.org>
Date: Tue, 28 Nov 2023 22:03:48 +0100
Subject: [PATCH] patch 9.0.2140: [security]: use-after-free in win-enter

Problem:  [security]: use-after-free in win-enter
Solution: validate window pointer before calling win_enter()

win_goto() may stop visual mode, if it is active. However, this may in
turn trigger the ModeChanged autocommand, which could potentially free
the wp pointer which was valid before now became stale and points to now
freed memory.

So before calling win_enter(), let's verify one more time, that the
wp pointer still points to a valid window structure.

Reported by @henices, thanks!

Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/testdir/crash/poc_win_enter_ext | Bin 0 -> 1958 bytes
 src/testdir/test_crash.vim          |   8 ++++++++
 src/version.c                       |   2 ++
 src/window.c                        |   6 ++++++
 4 files changed, 16 insertions(+)
 create mode 100644 src/testdir/crash/poc_win_enter_ext

diff --git a/src/testdir/crash/poc_win_enter_ext b/src/testdir/crash/poc_win_enter_ext
new file mode 100644
index 0000000000000000000000000000000000000000..73f53b575b699046d6bdc5402083dfa9c278769a
GIT binary patch
literal 1958
zcmd^9L2FY%5Z-|Akcri43qb{O0-=Jo65`23usv7{K}3RhNhsFcCWV*x@V$s03`vig
z3ZB)g1ia{>{sPZA<lx<3P!T)?FYD~SCTZkFk3yZpd%H8UJM(?>u{VSUu{8i6hx_5y
zV1H?;Fu;W1y>n;zB5;HdNPy=Djlu&&Jc;wfKg8RU^(Dls38aAV5#k*C{mn)p#Af$|
z`_^@#O{F|YY774GP3w1|nFH6m;?@<FiAuZ`&{{8r*CA9Cw(iLnb+G~~;-)R@IO&EX
zrP?N_DUjVFt$slv1CT*VLq|VT2|x{xLBG<xr&Y<D9}jgU-);&5nS)JJV+zvn?~oX8
zi2bkqe!s$IAsdi(F~&JgN-lQNwWJBo&D)go`13R`PL-{N7Nh4cN?{lfmXAEBTUjz@
zDKOZo9TJ)MfD^(@XhZCp6TiW2=Bk_-T`B2WL@_gK(TWV0DJ__CoF_nO<$5F1DQilT
zbu@FPo@uJg9C0qsDKGfm1>05iY&*IDKeH14NE@rb*m9yZO%k)GE0tt&REH6DU6#T$
z#*r{Kj8aT{N(U-x(Fo;TIcxe^J2xc^Y!uUJ#}zO4;68N02xHq1Xd;fI!iYqXfZA&a
zJhu*th}qW{48x<|4ml9wOuSsIp1F0F4}baKxNWgJp*I?6>4>JMw0t@J#?0EZI~wZK
z7!7lqoRx>~Q6)R<-Yok_wc)H7`#;QxJ&*DKw_0*|F#k+XhwtMt)l`hkj-4wLhv-wB
kbK+a;_22+f{79z`^d3}HQGA0`3ZCqE(kJ^S^AjU~0iVaYUjP6A

literal 0
HcmV?d00001

diff --git a/src/testdir/test_crash.vim b/src/testdir/test_crash.vim
index b093b053c5..11c5f4e014 100644
--- a/src/testdir/test_crash.vim
+++ b/src/testdir/test_crash.vim
@@ -128,6 +128,13 @@ func Test_crash1_2()
     \ '  && echo "crash 1: [OK]" > '.. result .. "\<cr>")
   call TermWait(buf, 150)
 
+  let file = 'crash/poc_win_enter_ext'
+  let cmn_args = "%s -u NONE -i NONE -n -e -s -S %s -c ':qa!'"
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args ..
+    \ '  && echo "crash 2: [OK]" >> '.. result .. "\<cr>")
+  call TermWait(buf, 350)
+
   " clean up
   exe buf .. "bw!"
 
@@ -135,6 +142,7 @@ func Test_crash1_2()
 
   let expected = [
       \ 'crash 1: [OK]',
+      \ 'crash 2: [OK]',
       \ ]
 
   call assert_equal(expected, getline(1, '$'))
diff --git a/src/version.c b/src/version.c
index 3fc23c17e5..e32e5c006d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2140,
 /**/
     2139,
 /**/
diff --git a/src/window.c b/src/window.c
index 0f4363b942..be010dc7fd 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5013,6 +5013,7 @@ tabpage_move(int nr)
  * Go to another window.
  * When jumping to another buffer, stop Visual mode.  Do this before
  * changing windows so we can yank the selection into the '*' register.
+ * (note: this may trigger ModeChanged autocommand!)
  * When jumping to another window on the same buffer, adjust its cursor
  * position to keep the same Visual area.
  */
@@ -5039,10 +5040,15 @@ win_goto(win_T *wp)
     }
 
     if (wp->w_buffer != curbuf)
+	// careful: triggers ModeChanged autocommand
 	reset_VIsual_and_resel();
     else if (VIsual_active)
 	wp->w_cursor = curwin->w_cursor;
 
+    // autocommand may have made wp invalid
+    if (!win_valid(wp))
+	return;
+
 #ifdef FEAT_GUI
     need_mouse_correct = TRUE;
 #endif