patch 8.2.3741: using freed memory in open command

Problem:    Using freed memory in open command.
Solution:   Make a copy of the current line.

src/ex_docmd.c

@@ -6877,13 +6877,17 @@ ex_open(exarg_T *eap)
 	regmatch.regprog = vim_regcomp(eap->arg, magic_isset() ? RE_MAGIC : 0);
 	if (regmatch.regprog != NULL)
 	{
+	    // make a copy of the line, when searching for a mark it might be
+	    // flushed
+	    char_u *line = vim_strsave(ml_get_curline());
+
 	    regmatch.rm_ic = p_ic;
-	    p = ml_get_curline();
-	    if (vim_regexec(&regmatch, p, (colnr_T)0))
-		curwin->w_cursor.col = (colnr_T)(regmatch.startp[0] - p);
+	    if (vim_regexec(&regmatch, line, (colnr_T)0))
+		curwin->w_cursor.col = (colnr_T)(regmatch.startp[0] - line);
 	    else
 		emsg(_(e_nomatch));
 	    vim_regfree(regmatch.regprog);
+	    vim_free(line);
 	}
 	// Move to the NUL, ignore any other arguments.
 	eap->arg += STRLEN(eap->arg);

src/testdir/test_ex_mode.vim

@@ -121,6 +121,19 @@ func Test_open_command()
   close!
 endfunc
 
+func Test_open_command_flush_line()
+  " this was accessing freed memory: the regexp match uses a pointer to the
+  " current line which becomes invalid when searching for the ') mark.
+  new
+  call setline(1, ['one', 'two. three'])
+  s/one/ONE
+  try
+    open /\%')/
+  catch /E479/
+  endtry
+  bwipe!
+endfunc
+
 " Test for :g/pat/visual to run vi commands in Ex mode
 " This used to hang Vim before 8.2.0274.
 func Test_Ex_global()

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3741,
 /**/
     3740,
 /**/