Paul Eggert wrote:
> there are races on GNU/Linux which can lead to potential security problems. 
> Perhaps we can't fix these races on MS-Windows but we should be able to fix them 
> on a GNUish host. However, we will need to change the semantics of rename-file 
> etc. slightly, since no single system call supports the cp-like target rewriting 
> of these functions. I have a fix in mind to do that in a hopefully 
> compatible-enough way, which I'll try to propose soon. I'll keep 
> case-insensitive file systems in mind when I do that.

Attached is a proposed patch to fix this security problem. If I understand 
things correctly, the fix should work on MS-Windows and on case-insensitive file 
systems. Since this patch entails an incompatible change to the (undocumented) 
behavior of (rename-file A B) when B is a directory but is not a directory name, 
I'll mention the proposed change on emacs-devel.