Re: clearenv(3): implies that it's a security tool

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 18 February 2016 at 21:34, Matt Zimmerman <mdz-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org> wrote:
> Thanks for following up.  My recommendation is to say something like:
>
> This function DOES NOT securely erase the contents of the environment.
> Security-conscious applications which need to do this should use ....
> instead.

So, I think this report is a little confused, but mainly because of
the poor description in the man page.

The security-conscious applications in this context are those that
want to precisely control the environment passed to an exec()ed
program. clearenv() cannot, indeed must not, try to erase the buffers
containing the environment definitions. (See putenv(3) to understand
why.) I've adjusted the man page in away that I hope explains things
better:

       The  clearenv()  function  may  be  useful  in security-conscious
       applications that want to precisely control the environment  that
       is  passed  to  programs executed using exec(3).  The application
       would do this by first clearing the environment and  then  adding
       select environment variables.

       Note that the main effect of clearenv() is to adjust the value of
       the pointer environ(7); this function does not erase the contents
       of the buffers containing the environment definitions.

Cheers,

Michael
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