having horrors untainting a path string for moving a file

leocharre has asked for the wisdom of the Perl Monks concerning the following question:

I need to let users via a web interface, to tell the server to move a file from one place to another (i don't like this either).

This file is on a chunk of filetree that is mounted... So, it seems I need to use backticks and mv command. stuff like File::Copy will not steadily work accross filesystems

I'm running -Tw, and it's getting really angry at me for this.. I'm having a hard time untainting paths like /this/that/that/etc

I get this: Insecure $ENV{PATH} while running with -T switch at move.cgi line 148

This is my untainting and moving..

my %a=();
#their files may have @ signs, yea.. sigh
# from
if ("$$DMS{CONF}{DOC}/$filepath"=~m/^([\/_\@\w .-]+)$/){

    $a{from} = $1;
}

#to
if ("$$DMS{CONF}{DOC}/$$DMS{S}{session_file}/$$DMS{F}{$filepath}{file_
+name}"=~m/^([\/_\@\w .-]+)$/){
    $a{to}=$1;
}


$a{from}=~m/\w/ or die("from failed untaint");
$a{to}=~m/\w/ or die("to failed untaint");

my $err = `mv "$a{from}" "$a{to}"`; # and here we freak out
    
if ($err){ die("mov problem.. [$err]"); }
[download]

Is there some other way I should be untainting a path?

Comment on having horrors untainting a path string for moving a file Select or Download Code

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Re: having horrors untainting a path string for moving a file by virtualsue (Vicar) on Mar 14, 2006 at 18:39 UTC
Insecure $ENV{PATH} while running with -T switch at move.cgi line 148 This error message is trying to tell you to tighten down the $PATH environment setting. What I do is set $ENV{PATH} to '' (clear it) and use a known _absolute_ path for every external program being executed. /bin/mv, /bin/rm, etc. Taint is trying to protect you from being easy prey for a trojan horse attack.	[reply]
Re: having horrors untainting a path string for moving a file by ikegami (Patriarch) on Mar 14, 2006 at 18:37 UTC
You need to untaint `$ENV{PATH}` because the user could change it to run his `mv` instead of the system one. This is particularly relevant in setuid scripts. In this case, why don't you do `rename $a{from}, $a{to} or die("mov problem.. [$!]");` [download]	[reply] [d/l] [select]
Re^2: having horrors untainting a path string for moving a file by Fletch (Bishop) on Mar 14, 2006 at 18:47 UTC
The OP mentioned this may have to work across different mount points, and rename can't do that. And this is why he can't use File::Copy's `mv` since under the hood that also uses rename.	[reply] [d/l]
Re^3: having horrors untainting a path string for moving a file by ikegami (Patriarch) on Mar 14, 2006 at 18:50 UTC
Me bad! I didn't notice that. In that case, `File::Copy::move($a{from}, $a{to});` [download] or `system('/bin/mv', $a{from}, $a{to});` [download] is much safer! He'll might still need to untaint `$ENV{PATH}` (by setting it to a known value), but there's no shell involved. `mv` sets the error result, so that can be used instead of capturing the output.	[reply] [d/l] [select]