On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:
> A common pattern for syscall extensions is increasing the size of a
> struct passed from userspace, such that the zero-value of the new fields
> result in the old kernel behaviour (allowing for a mix of userspace and
> kernel vintages to operate on one another in most cases). This is done
> in both directions -- hence two helpers -- though it's more common to
> have to copy user space structs into kernel space.
>
> Previously there was no common lib/ function that implemented
> the necessary extension-checking semantics (and different syscalls
> implemented them slightly differently or incompletely[1]). A future
> patch replaces all of the common uses of this pattern to use the new
> copy_struct_{to,from}_user() helpers.
>
> [1]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
> similar checks to copy_struct_from_user() while rt_sigprocmask(2)
> always rejects differently-sized struct arguments.
>
> Suggested-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx>
I would probably split this out into a separate patchset. It can very
well go in before openat2(). Thoughts?
Christian
