(krb5kdc): NULL pointer dereference in the TGS handling (MITKRB5-SA-2011-007)

The process_tgs_req function in do_tgs_req.c in the Key Distribution Center (KDC) in MIT Kerberos 5 (aka krb5) 1.9 through 1.9.2 allows remote authenticated users to cause a denial of service (NULL pointer dereference and daemon crash) via a crafted TGS request that triggers an error other than the KRB5_KDB_NOENTRY error.