Re: [PATCH v4 0/4] lib: introduce copy_struct_from_user() helper

Christian Brauner
2019-10-01T16:01:45Z

On Tue, Oct 01, 2019 at 11:10:51AM +1000, Aleksa Sarai wrote:
> Patch changelog:
> v4:
> * __always_inline copy_struct_from_user(). [Kees Cook]
> * Rework test_user_copy.ko changes. [Kees Cook]
> v3: <https://lore.kernel.org/lkml/20190930182810.6090-1-cyphar@cyphar.com/>
> <https://lore.kernel.org/lkml/20190930191526.19544-1-asarai@suse.de/>
> v2: <https://lore.kernel.org/lkml/20190925230332.18690-1-cyphar@cyphar.com/>
> v1: <https://lore.kernel.org/lkml/20190925165915.8135-1-cyphar@cyphar.com/>
>
> This series was split off from the openat2(2) syscall discussion[1].
> However, the copy_struct_to_user() helper has been dropped, because
> after some discussion it appears that there is no really obvious
> semantics for how copy_struct_to_user() should work on mixed-vintages
> (for instance, whether [2] is the correct semantics for all syscalls).
>
> 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).
>
> Previously there was no common lib/ function that implemented
> the necessary extension-checking semantics (and different syscalls
> implemented them slightly differently or incompletely[3]). This series
> implements the helper and ports several syscalls to use it.
>
> Some in-kernel selftests are included in this patch. More complete
> self-tests for copy_struct_from_user() are included in the openat2()
> patchset.
>
> [1]: https://lore.kernel.org/lkml/20190904201933.10736-1-cyphar@cyphar.com/
>
> [2]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
> robustify sched_read_attr() ABI logic and code")
>
> [3]: 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.
>
> Aleksa Sarai (4):
> lib: introduce copy_struct_from_user() helper
> clone3: switch to copy_struct_from_user()
> sched_setattr: switch to copy_struct_from_user()
> perf_event_open: switch to copy_struct_from_user()
>
> include/linux/bitops.h | 7 ++
> include/linux/uaccess.h | 70 +++++++++++++++++++
> include/uapi/linux/sched.h | 2 +
> kernel/events/core.c | 47 +++----------
> kernel/fork.c | 34 ++--------
> kernel/sched/core.c | 43 ++----------
> lib/strnlen_user.c | 8 +--
> lib/test_user_copy.c | 136 +++++++++++++++++++++++++++++++++++--
> lib/usercopy.c | 55 +++++++++++++++
> 9 files changed, 288 insertions(+), 114 deletions(-)

I've picked this up now and it's sitting in
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=copy_struct_from_user

It should show up in linux-next tomorrow. I will let this sit there for
a few days but overall this seems good to have in rc2.
If someone objects and prefers to take it through their tree I can drop
it.

Christian