Re: access(2)--a security hole?

[scs () lokkur dexter mi us (Steve Simmons)]

In bugtraq various folks wrote:

> The security hole in access() is really that it has an implicit race
> condition in it.  You check a file, and then you assume moments later that
> the same access is granted.  So, if the file is a really a symlink, and
> someone changes where it points to between the access() and the open(), a
> completely different file might be affected.  This is the root of many of
> the holes that get posted here (xterm, /bin/mail come to mind).

The obvious correct coding is to open *first*, then check access, and
close it back up if you shouldn't have opened it.