On Wed, Sep 25, 2019 at 06:59:11PM +0200, Aleksa Sarai wrote: > 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@xxxxxxxxxx/ > > [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. Thank for splitting this out! :) I should be able to review this tomorrow. Christian
