patch 8.2.4969: changing text in Visual mode may cause invalid memory access

Problem:    Changing text in Visual mode may cause invalid memory access.
Solution:   Check the Visual position after making a change.

src/change.c

@@ -548,6 +548,9 @@ changed_common(
 	curwin->w_changelistidx = curbuf->b_changelistlen;
     }
 
+    if (VIsual_active)
+	check_visual_pos();
+
     FOR_ALL_TAB_WINDOWS(tp, wp)
     {
 	if (wp->w_buffer == curbuf)

src/edit.c

@@ -2541,16 +2541,8 @@ stop_insert(
 
 	    // <C-S-Right> may have started Visual mode, adjust the position for
 	    // deleted characters.
-	    if (VIsual_active && VIsual.lnum == curwin->w_cursor.lnum)
-	    {
-		int len = (int)STRLEN(ml_get_curline());
-
-		if (VIsual.col > len)
-		{
-		    VIsual.col = len;
-		    VIsual.coladd = 0;
-		}
-	    }
+	    if (VIsual_active)
+		check_visual_pos();
 	}
     }
     did_ai = FALSE;

src/misc2.c

@@ -622,6 +622,31 @@ check_cursor(void)
     check_cursor_col();
 }
 
+/*
+ * Check if VIsual position is valid, correct it if not.
+ * Can be called when in Visual mode and a change has been made.
+ */
+    void
+check_visual_pos(void)
+{
+    if (VIsual.lnum > curbuf->b_ml.ml_line_count)
+    {
+	VIsual.lnum = curbuf->b_ml.ml_line_count;
+	VIsual.col = 0;
+	VIsual.coladd = 0;
+    }
+    else
+    {
+	int len = (int)STRLEN(ml_get(VIsual.lnum));
+
+	if (VIsual.col > len)
+	{
+	    VIsual.col = len;
+	    VIsual.coladd = 0;
+	}
+    }
+}
+
 #if defined(FEAT_TEXTOBJ) || defined(PROTO)
 /*
  * Make sure curwin->w_cursor is not on the NUL at the end of the line.
@@ -2416,7 +2441,7 @@ get_user_name(char_u *buf, int len)
     return OK;
 }
 
-#if defined(EXITFREE) || defined(PROTOS)
+#if defined(EXITFREE) || defined(PROTO)
 /*
  * Free the memory allocated by get_user_name()
  */

src/proto/misc2.pro

@@ -17,6 +17,7 @@ void check_cursor_lnum(void);
 void check_cursor_col(void);
 void check_cursor_col_win(win_T *win);
 void check_cursor(void);
+void check_visual_pos(void);
 void adjust_cursor_col(void);
 int leftcol_changed(void);
 int copy_option_part(char_u **option, char_u *buf, int maxlen, char *sep_chars);

src/testdir/test_visual.vim

@@ -1296,6 +1296,16 @@ func Test_visual_block_append_invalid_char()
   set isprint&
 endfunc
 
+func Test_visual_block_with_substitute()
+  " this was reading beyond the end of the line
+  new
+  norm a0)
+  sil! norm  O
+  s/)
+  sil! norm 
+  bwipe!
+endfunc
+
 func Test_visual_reselect_with_count()
   " this was causing an illegal memory access
   let lines =<< trim END

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4969,
 /**/
     4968,
 /**/