udf: prevent speculative execution

udf: prevent speculative execution

Since the eahd->appAttrLocation value in function
udf_add_extendedattr() seems to be controllable by
userspace and later on conditionally (upon bound check)
used in following memmove, insert an observable speculation
barrier before its usage. This should prevent
observable speculation on that branch and avoid
kernel memory leak.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Orabug: 27340445
CVE: CVE-2017-5753

Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>
Reviewed-by: John Haxby <john.haxby@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>