drbd: Work on permission enforcement

Now we have the capabilities of the sending process available,
use them to enforce CAP_SYS_ADMIN.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/drbd/drbd_nl.c

@@ -2000,7 +2000,7 @@ static struct cn_handler_struct cnd_table[] = {
 	[ P_new_c_uuid ]	= { &drbd_nl_new_c_uuid,	0 },
 };
 
-static void drbd_connector_callback(struct cn_msg *req)
+static void drbd_connector_callback(struct cn_msg *req, struct netlink_skb_parms *nsp)
 {
 	struct drbd_nl_cfg_req *nlp = (struct drbd_nl_cfg_req *)req->data;
 	struct cn_handler_struct *cm;
@@ -2017,6 +2017,11 @@ static void drbd_connector_callback(struct cn_msg *req)
 		return;
 	}
 
+	if (!cap_raised(nsp->eff_cap, CAP_SYS_ADMIN)) {
+		retcode = ERR_PERM;
+		goto fail;
+	}
+
 	mdev = ensure_mdev(nlp);
 	if (!mdev) {
 		retcode = ERR_MINOR_INVALID;

include/linux/drbd.h

@@ -138,6 +138,7 @@ enum drbd_ret_codes {
 	ERR_VERIFY_RUNNING	= 149, /* DRBD 8.2 only */
 	ERR_DATA_NOT_CURRENT	= 150,
 	ERR_CONNECTED		= 151, /* DRBD 8.3 only */
+	ERR_PERM		= 152,
 
 	/* insert new ones above this line */
 	AFTER_LAST_ERR_CODE