]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
lib: introduce copy_struct_from_user() helper
authorAleksa Sarai <cyphar@cyphar.com>
Tue, 1 Oct 2019 01:10:52 +0000 (11:10 +1000)
committerChristian Brauner <christian.brauner@ubuntu.com>
Tue, 1 Oct 2019 13:45:03 +0000 (15:45 +0200)
commitf5a1a536fa14895ccff4e94e6a5af90901ce86aa
tree04c131cf6206c2dc929dd2ccf6341adfa1a2e814
parent54ecb8f7028c5eb3d740bb82b0f1d90f2df63c5c
lib: introduce copy_struct_from_user() helper

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).

While this interface exists for communication in both directions, only
one interface is straightforward to have reasonable semantics for
(userspace passing a struct to the kernel). For kernel returns to
userspace, what the correct semantics are (whether there should be an
error if userspace is unaware of a new extension) is very
syscall-dependent and thus probably cannot be unified between syscalls
(a good example of this problem is [1]).

Previously there was no common lib/ function that implemented
the necessary extension-checking semantics (and different syscalls
implemented them slightly differently or incompletely[2]). Future
patches replace common uses of this pattern to make use of
copy_struct_from_user().

Some in-kernel selftests that insure that the handling of alignment and
various byte patterns are all handled identically to memchr_inv() usage.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

[2]: 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>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191001011055.19283-2-cyphar@cyphar.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
include/linux/bitops.h
include/linux/uaccess.h
lib/strnlen_user.c
lib/test_user_copy.c
lib/usercopy.c