integrity: prevent loading untrusted certificates on the IMA trusted keyring

If IMA_LOAD_X509 is enabled, either directly or indirectly via
IMA_APPRAISE_SIGNED_INIT, certificates are loaded onto the IMA
trusted keyring by the kernel via key_create_or_update(). When
the KEY_ALLOC_TRUSTED flag is provided, certificates are loaded
without first verifying the certificate is properly signed by a
trusted key on the system keyring.  This patch removes the
KEY_ALLOC_TRUSTED flag.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>
Cc:  <stable@vger.kernel.org> # 3.19+
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/digsig.c

@@ -105,7 +105,7 @@ int __init integrity_load_x509(const unsigned int id, const char *path)
 				   rc,
 				   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
 				    KEY_USR_VIEW | KEY_USR_READ),
-				   KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_TRUSTED);
+				   KEY_ALLOC_NOT_IN_QUOTA);
 	if (IS_ERR(key)) {
 		rc = PTR_ERR(key);
 		pr_err("Problem loading X.509 certificate (%d): %s\n",