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    SubjectRe: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers
    On 2019-09-05, Christian Brauner <christian.brauner@ubuntu.com> wrote:
    > 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@rasmusvillemoes.dk>
    > > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
    >
    > 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/>
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