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Subject[PATCH v1 0/4] lib: introduce copy_struct_from_user() helper
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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.

[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/uaccess.h | 4 +++
include/uapi/linux/sched.h | 2 ++
kernel/events/core.c | 47 +++++-------------------
kernel/fork.c | 34 ++++--------------
kernel/sched/core.c | 43 ++++------------------
lib/Makefile | 2 +-
lib/strnlen_user.c | 52 +++++++++++++++++++++++++++
lib/struct_user.c | 73 ++++++++++++++++++++++++++++++++++++++
8 files changed, 155 insertions(+), 102 deletions(-)
create mode 100644 lib/struct_user.c

--
2.23.0

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