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Subject[PATCH v2 0/4] lib: introduce copy_struct_from_user() helper
Date
Patch changelog:
v2:
* Switch to less buggy handling of alignment. [Linus Torvalds, Al Viro]
* Move is_zeroed_user() to lib/usercopy.c. [kbuild test robot]
* Move copy_struct_to_user() to lib/usercopy.c. [Christian Brauner]
* Add self-tests for is_zeroed_user() to lib/test_user_copy.c.
[Christian Brauner]
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.

[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 | 4 ++
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 | 59 +++++++++++++++++--
lib/usercopy.c | 115 +++++++++++++++++++++++++++++++++++++
9 files changed, 205 insertions(+), 114 deletions(-)

--
2.23.0

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