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 > 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). Logically, I agree. I'm more worried about the behavioral change -- if we don't remove the fd on failure, the fd is installed with no indication to the process that it exists (it won't know the close it -- if it keeps running -- and it may survive across exec). Before, it never entered the file table. > You can actually see that even scm_detach_fds() currently just > silently swallows errors if writing some header fields fails at the > end. Yeah, and it's a corner case. But it should be possible (trivial, even) to clean up on failure to retain the original results. -- Kees Cook
