Re: if file exist

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Keith Thompson <kst@cts.com> writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> [...]
> > I'm not sure what the second command is attempting to do, but I'm pretty
> > sure that on Unix systems, if you have no access to directory "dir"
> > (i.e., rwx bits all zero), then you can't find out whether a given file
> > name exists in dir.  E.g., "ls dir/exists" and "ls dir/not-exists" will
> > both produce the same error message, even though exists exists and
> > not-exists does not.  Attempting to run a directory as a command will
> > cause an error, too, so I don't see how the second command causes a
> > security flaw.  Please explain the 'ls `dirname filename`'.
> 
> I think you missed the backticks and/or the fact that "dirname" is a
> Unix command that prints a given filename with the trailing component
> removed.

I missed the fact that "dirname" was the dirname command.
I thought it meant "the name of some directory".

I still don't see how this introduces a security hole.
The dirname command just works on a string -- it doesn't care whether
the given file and directory names exist.  And 'ls' won't tell you
whether the file exists either.

(The security hole in question is when I have a private directory foo,
can outsiders find out the name(s) of my files in foo.)

- Bob