[fpc-pascal] GetTempFileName in Linux

[Michael Van Canneyt]

On Wed, 6 Oct 2010, Jonas Maebe wrote:

>
> On 06 Oct 2010, at 11:05, Michael Van Canneyt wrote:
>
>> On Wed, 6 Oct 2010, Jonas Maebe wrote:
>> 
>>> On 06 Oct 2010, at 09:41, Michael Van Canneyt wrote:
>>> 
>>>> This is always true on Unix, the only way to make sure is to have the 
>>>> kernel
>>>> create the temporary name and file for you. Unix - to my knowledge - does 
>>>> not have a way to create and lock a file in one atomic operation; There 
>>>> are
>>>> always 2 operations involved, and so anything can happen between the 2
>>>> calls.
>>> 
>>> You can at least open a file with O_CREAT|O_EXCL|O_NOFOLLOW to make sure 
>>> that it does not yet exist at the point that you create it (and that it's 
>>> not a symlink either).
>> 
>> This is correct, but doesn't lock the file,
>
> Locking is always advisory on Unix, so that doesn't matter anyway.
>
>> and so it doesn't prevent
>> someone from 'stealing' the file before the lock is applied.
>
> Nobody else can steal the file once you have created it, because they won't 
> be the owner nor have the necessary permissions. That is the main security 
> risk and it is solved by this approach. The fact that another process running 
> under your login not using O_EXCL could overwrite it is not an extra security 
> risk (if you have a rogue process running under your login, nothing that you 
> do is safe because it can use ptrace to modify any process in any way it sees 
> fit anyway).

And that is why I think the whole point is hugely exaggerated :-)

But it doesn't mean we shouldn't do our best to make it minimally safe.

Michael.