Re: [NSE] Adding mkdir support

[Patrick Donnelly <batrick () batbytes com>]

On Wed, Apr 4, 2012 at 3:55 PM, Djalal Harouni <tixxdz () opendz org> wrote:
> Hi Patrik,
>
> On Sat, Mar 31, 2012 at 10:20:09PM +0200, Patrik Karlsson wrote:
> > Hi Djalal,
> >
> > Your comment got me thinking and while working on the luadoc documentation
> > I went through all of the functionality the fs library provides. To be
> > honest, I don't think it should be a problem including any of the functions.
> Ok, I took a quick look, and I think that we should modify the following:
>
> make_dir() function calls mkdir() in this way:
>
>   mkdir (path, S_IRUSR | S_IWUSR | S_IXUSR | S_IRGRP |
>                S_IWGRP | S_IXGRP | S_IROTH | S_IXOTH );
>                ^^^^^^^
>
> At least we should use 0755 regardless of the current value of umask
> and avoid situations where groups are shared...
>
> Other solutions:
> 1) use 0700 mode ? (I like this one).
> 2) add an extra argument to control the mode ?
>
> David, Patrick what do you think ? should we report this upstream ?

I believe the reason they don't support a mode argument for mkdir is
because it's not supported for Windows. In any case, I agree that 0700
is the correct mode. It should be reported upstream.

> BTW while we are at this thing, IMHO we should add checks to only write
> to directories owned by the current user and writable only by the current
> user, and try to avoid issues that can raise from following crafted urls
> and links from servers. Perhaps we should define something like "/" root
> directory and write all the stuff there in case...

I really think we should avoid modifying lfs as much as possible. The
main reason I encouraged using lfs is because it is fairly standard in
the community and mostly portable.

> > something searching for this when new code is committed as an additional
> > check maybe?
> That would be nice, a simple script that evaluates or identifies Lua
> functions will help.
>
> This can be a simple and nice GSoC task.

This is non-trivial. It is quite easy to have Lua code reference
something like os.execute without actually being obvious (from a code
analysis standpoint) about it:

local os = require "os"

os[string.gsub("dwdbtsd", ".", function(a) return
string.char(string.byte(a)+1) end)]("echo hi")

Of course that's suspicious code but you get the idea. The only safe
thing to do is remove os.execute which is not something we've wanted
to do in the past. I also use the term "safe" cautiously. I don't
think we can ever truly protect against malicious scripts without
seriously hamstringing the available freedoms scripts currently enjoy.

-- 
- Patrick Donnelly
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