IMA: prevent keys on the .ima_blacklist from being removed

Set the KEY_FLAGS_KEEP on the .ima_blacklist to prevent userspace
from removing keys from the keyring.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_mok.c

@@ -47,7 +47,9 @@ __init int ima_mok_init(void)
 	if (IS_ERR(ima_mok_keyring) || IS_ERR(ima_blacklist_keyring))
 		panic("Can't allocate IMA MOK or blacklist keyrings.");
 	set_bit(KEY_FLAG_TRUSTED_ONLY, &ima_mok_keyring->flags);
+
 	set_bit(KEY_FLAG_TRUSTED_ONLY, &ima_blacklist_keyring->flags);
+	set_bit(KEY_FLAG_KEEP, &ima_blacklist_keyring->flags);
 	return 0;
 }