Overwriting paging files

[Guy Harris]

> >In a system using NFS ... if the process using that file tries to
> >fetch a page from a file that has been modified since the process
> >in question first attached to it, it gets zapped by a SIGKILL (a
> >message is printed on the user's terminal, if there's a terminal
> >associated with this process).
> 
> Not very nice.  It would be better if the pages were brought over
> and stored locally until the process is done with them.  This could
> be done as a `background task', to keep it from affecting performance
> much.

When would the pages be brought over?  When the program was first executed?
This may narrow the window of vulnerability, but it wouldn't close it
entirely.  I also wouldn't go so far as to say doing it as a background task
wouldn't affect performance much, without seeing some hard data - if the
program is very big, you will be tying your network and your server's disk
up fetching a bunch of pages which, presumably, you'll not be using.

When the file is written?  No can do.  The file may be written by another
machine, so you have no way of knowing it's being written.
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy at sun.com (or guy at sun.arpa)