Re: [PATCH v2 2/2] rusage: allow 64-bit times ru_utime/ru_stime

[Ingo Molnar <mingo@kernel.org>]

* Eric W. Biederman <ebiederm@xmission.com> wrote:

> Ingo Molnar <mingo@kernel.org> writes:
> 
> > * Eric W. Biederman <ebiederm@xmission.com> wrote:
> >
> >> The trouble with attributes is that means you can't filter your system
> >> call arguments with seccomp. [...]
> >
> > There's nothing keeping seccomp from securely fetching those arguments and 
> > extending filtering to them as well ...
> >
> > Allowing that would make sense for a lot of other system calls as
> > well.
> 
> Possibly.  The challenge is that if the fetch for the kernel to use
> those arguments is different from the fetch of seccomp to test those
> arguments you have a time of test vs time of use race.

Those fetched values should obviously then be used to call permitted system calls.

> Given the location of the seccomp hook at the kernel user space border
> there is no easy way for seccomp to share the fetch with the system
> call itself.
> 
> So I don't see how seccomp could perform the fetch securely.

Looks like more of a seccomp mis-design/mis-implementation than some fundamental 
problem.

Mis-designed security features should not hinder system call design.

Thanks,

	Ingo