Re: Hide command line arguments

[Bob Proulx]

Martin Bernreuther wrote:
> on a common Linux system, everyone can use e.g.
> ps and will see running processes of all users including
> the command line arguments.

Yes.  This is a long standing reason that programs that deal with
secure data such as passwords should avoid putting passwords in the
argument list, for example.

> I'd like to hide the command line arguments e.g. for the cp command,
> which sometimes uses quite a long time to copy large files, to keep
> the path and file names secret.

I suggest using the 'rsync --from0 --files-from=FILE' options.  This
will read a list of files (optionally from stdin if FILE is "-") and
therefore the filenames will never appear in the argument list of the
process.

Another alternative is to use the 'cp -R' to copy a directory of
files.  In that case cp reads the directory listing itself and
therefore the filenames are never in the argument list.

> Writing a small C program, it's quite easy to
> overwrite all chars of the argv[] strings with 0
> after the commandline options are being processed.
> 
> Is there a possibility to activate such a feature
> in e.g. cp? (like cp --hideargs ...)

Unfortunately that doesn't really work.  If a ps is done very quickly
after the program starts but before it can obscure the argument list
then the values are still seen.  It reduces the time that arguments
are exposed but this creates a false sense of security.  This false
sense of security may be worse because it would lead people to believe
they are safe when they are not.

If you really need to hide the files then it is better to solve the
problem 100% and _never_ put the filename in the argument list.  That
means that the list of files needs to read by the program by other
means.  Either by having the program read the directory itself or by
passing it a list through the environment or by passing it a list by
file.

The rsync command seems perfectly fitted to this task.  Although I
will admit that sending the list of files to copy to it through a
file/stdin is slightly more involved than cp.  But here since you are
wanting more then a little more work to get it seems reasonable.

Bob