PHP3 safe_mode and popen()

[kris () KOEHNTOPP DE (Kristian Koehntopp)]

PHP3 (http://www.php.net) is a scripting language used in many
webhosting setups. Often in hosting setups so called "safe_mode"
is enabled, which restricts the user in many ways. For example,
in safe_mode you are supposed to be able to execute only
programs from a safe_mode_exec_dir, if one is defined. Within
that directory there should be only a restricted command set
that is considered safe.

When safe_mode is enabled, PHP3 is supposed to apply
EscapeShellCmd() to each shell command to prevent the user from
breaking out of this directory. As it turns out, the popen()
function does not do this in safe_mode. I was able to set up a
web server with safe_mode enabled and a safe_mode_exec_dir
containing only "ls". I then wrote the following script:

<?php
  $fp = popen("ls -l /opt/bin; /usr/bin/id", "r");
  echo "$fp<br>\n";
  while($line = fgets($fp, 1024)):
    printf("%s<br>\n", $line);
  endwhile;
  pclose($fp);

  phpinfo();
 ?>

which gave me the following output

1
total 53
-rwxr-xr-x 1 root root 52292 Jan 3 22:05 ls
uid=30(wwwrun) gid=65534(nogroup) groups=65534(nogroup)

and from the configuration values of phpinfo():

safe_mode            0             1

The following patch against functions/file.c fixes the problem,
I hope:

Index: functions/file.c
===================================================================
RCS file: /repository/php3/functions/file.c,v
retrieving revision 1.229
retrieving revision 1.230
diff -u -r1.229 -r1.230
--- functions/file.c    2000/01/01 04:31:15     1.229
+++ functions/file.c    2000/01/03 21:31:31     1.230
@@ -26,7 +26,7 @@
    | Authors: Rasmus Lerdorf <rasmus () lerdorf on ca>                       |
    +----------------------------------------------------------------------+
  */
-/* $Id: file.c,v 1.229 2000/01/01 04:31:15 sas Exp $ */
+/* $Id: file.c,v 1.230 2000/01/03 21:31:31 kk Exp $ */
 #include "php.h"

 #include <stdio.h>
@@ -51,6 +51,7 @@
 #include "safe_mode.h"
 #include "php3_list.h"
 #include "php3_string.h"
+#include "exec.h"
 #include "file.h"
 #if HAVE_PWD_H
 #if MSVC5
@@ -575,7 +576,7 @@
        pval *arg1, *arg2;
        FILE *fp;
        int id;
-       char *p;
+       char *p, *tmp = NULL;
        char *b, buf[1024];
        TLS_VARS;

@@ -600,7 +601,11 @@
                } else {
                        snprintf(buf,sizeof(buf),"%s/%s",php3_ini.safe_mode_exec_dir,arg1->value.str.val);
                }
-               fp = popen(buf,p);
+
+               tmp = _php3_escapeshellcmd(buf);
+               fp = popen(tmp,p);
+               efree(tmp); /* temporary copy, no longer necessary */
+
                if (!fp) {
                        php3_error(E_WARNING,"popen(\"%s\",\"%s\") - %s",buf,p,strerror(errno));
                        RETURN_FALSE;

As a web hoster, you should not rely on safe_mode for security,
but use the CGI version of PHP in a chroot()ed environment
instead.

Kristian