Re: [PATCH] security/keyring: avoid pagefaults in keyring_read_iterator

[David Howells <dhowells@redhat.com>]

Chris von Recklinghausen <crecklin@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