Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers

On 2019-09-05, Christian Brauner [off-list ref] wrote:

On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:

quoted

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@rasmusvillemoes.dk>
Signed-off-by: Aleksa Sarai <redacted>

I would probably split this out into a separate patchset. It can very
well go in before openat2(). Thoughts?

Yeah, I'll split this and the related patches out -- though I will admit
I'm not sure how you're supposed to deal with multiple independent
patchsets that depend on each other. How will folks reviewing openat2(2)
know to include the lib/struct_user.c changes?

Also, whose tree should it go through?

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>