On 10/21/2019 10:21 AM, David Howells wrote: > Chris von Recklinghausen <creck...@redhat.com> wrote: > >> The put_user call from keyring_read_iterator caused a page fault which >> attempts to lock mm->mmap_sem and type->lock_class (key->sem) in the reverse >> order that keyring_read_iterator did, thus causing the circular locking >> dependency. >> >> Remedy this by using access_ok and __put_user instead of put_user so we'll >> return an error instead of faulting in the page. > I wonder if it's better to create a kernel buffer outside of the lock in > keyctl_read_key(). Hmmm... The reason I didn't want to do that is that > keyrings have don't have limits on the size. Maybe that's not actually a > problem, since 1MiB would be able to hold a list of a quarter of a million > keys. > > David >
Hi David, Thanks for the feedback. I can try to prototype that, but regardless of where the kernel buffer is allocated, the important part is causing the initial pagefault in the read path outside the lock so __put_user won't fail due to a valid user address but page backing the user address isn't in-core. I'll start work on v2. Thanks, Chris