[PATCH v6 2/8] nbd: disallow NBD_SET_SOCK on an active device

We cannot add a socket to an already running nbd device, the reconfigure
for netlink can only active an inactive socket. But for ioctl path, we can
call NBD_SET_SOCK after NBD_DO_IT, reject this using nbd->pid which has
been setted when NBD_DO_IT. Besides, it is the root cause for commit
b98e762e3d71 ("nbd: freeze the queue while we're adding connections").

Reviewed-by: Yu Kuai <[email protected]>
Signed-off-by: Yang Erkun <[email protected]>
---
 drivers/block/nbd.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b1a5acd57426..7ec85f94f742 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1278,6 +1278,13 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
 	/* Arg will be cast to int, check it to avoid overflow */
 	if (arg > INT_MAX)
 		return -EINVAL;
+
+	if (nbd->pid) {
+		dev_err(disk_to_dev(nbd->disk),
+			"Cannot add socket to a running device\n");
+		return -EBUSY;
+	}
+
 	sock = nbd_get_socket(nbd, arg, &err);
 	if (!sock)
 		return err;
-- 
2.52.0