In the Linux kernel, the following vulnerability has been resolved:
dax: read holder_ops once in dax_holder_notify_failure()
dax_holder_notify_failure() reads dax_dev->holder_ops twice without
READ_ONCE() — once for the NULL check and once for the indirect
notify_failure() call. A concurrent fs_put_dax() can clear holder_ops
between the two reads, so the check can observe a non-NULL pointer while
the call dereferences NULL. (kill_dax() also clears holder_ops, but only
after synchronize_srcu(), so it cannot race a reader that is inside
dax_read_lock(); fs_put_dax() does no such synchronization.)
Fetch holder_ops once into a local with READ_ONCE() so the NULL check and
the indirect call observe the same value.
