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

Aleksa Sarai
2019-10-01T01:10:51Z

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(-)

--
2.23.0