On Sat, May 30, 2020 at 05:17:24AM +0200, Jann Horn wrote: > On Sat, May 30, 2020 at 4:43 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > I mean, yes, that's certainly better, but it just seems a shame that > > everyone has to do the get_unused/put_unused dance just because of how > > SCM_RIGHTS does this weird put_user() in the middle. > > > > Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we > > move the put_user() after instead? > > Honestly, I think trying to remove file descriptors and such after > -EFAULT is a waste of time. If userspace runs into -EFAULT, userspace Agreed, we've never bothered with trying to recover from EFAULT. Just look at kernel/fork.c:_do_fork(): if (clone_flags & CLONE_PARENT_SETTID) put_user(nr, args->parent_tid); we don't even bother even though we technically could. > is beyond saving and can't really do much other than exit immediately. > There are a bunch of places that will change state and then throw > -EFAULT at the end if userspace supplied an invalid address, because > trying to hold locks across userspace accesses just in case userspace > supplied a bogus address is kinda silly (and often borderline > impossible). > > You can actually see that even scm_detach_fds() currently just > silently swallows errors if writing some header fields fails at the > end. There's really no point in trying to save a broken scm message imho.
