nbd: don't copy kernel creds

No need to copy kernel credentials.

Link: https://patch.msgid.link/20251103-work-creds-init_cred-v1-6-cb3ec8711a6a@kernel.org
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

drivers/block/nbd.c

@@ -52,7 +52,6 @@
 static DEFINE_IDR(nbd_index_idr);
 static DEFINE_MUTEX(nbd_index_mutex);
 static struct workqueue_struct *nbd_del_wq;
-static struct cred *nbd_cred;
 static int nbd_total_devices = 0;
 
 struct nbd_sock {
@@ -555,7 +554,6 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 	int result;
 	struct msghdr msg = {} ;
 	unsigned int noreclaim_flag;
-	const struct cred *old_cred;
 
 	if (unlikely(!sock)) {
 		dev_err_ratelimited(disk_to_dev(nbd->disk),
@@ -564,33 +562,32 @@ static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 		return -EINVAL;
 	}
 
-	old_cred = override_creds(nbd_cred);
-
 	msg.msg_iter = *iter;
 
 	noreclaim_flag = memalloc_noreclaim_save();
-	do {
-		sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
-		sock->sk->sk_use_task_frag = false;
-		msg.msg_flags = msg_flags | MSG_NOSIGNAL;
-
-		if (send)
-			result = sock_sendmsg(sock, &msg);
-		else
-			result = sock_recvmsg(sock, &msg, msg.msg_flags);
-
-		if (result <= 0) {
-			if (result == 0)
-				result = -EPIPE; /* short read */
-			break;
-		}
-		if (sent)
-			*sent += result;
-	} while (msg_data_left(&msg));
 
-	memalloc_noreclaim_restore(noreclaim_flag);
+	scoped_with_kernel_creds() {
+		do {
+			sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
+			sock->sk->sk_use_task_frag = false;
+			msg.msg_flags = msg_flags | MSG_NOSIGNAL;
 
-	revert_creds(old_cred);
+			if (send)
+				result = sock_sendmsg(sock, &msg);
+			else
+				result = sock_recvmsg(sock, &msg, msg.msg_flags);
+
+			if (result <= 0) {
+				if (result == 0)
+					result = -EPIPE; /* short read */
+				break;
+			}
+			if (sent)
+				*sent += result;
+		} while (msg_data_left(&msg));
+	}
+
+	memalloc_noreclaim_restore(noreclaim_flag);
 
 	return result;
 }
@@ -2683,15 +2680,7 @@ static int __init nbd_init(void)
 		return -ENOMEM;
 	}
 
-	nbd_cred = prepare_kernel_cred(&init_task);
-	if (!nbd_cred) {
-		destroy_workqueue(nbd_del_wq);
-		unregister_blkdev(NBD_MAJOR, "nbd");
-		return -ENOMEM;
-	}
-
 	if (genl_register_family(&nbd_genl_family)) {
-		put_cred(nbd_cred);
 		destroy_workqueue(nbd_del_wq);
 		unregister_blkdev(NBD_MAJOR, "nbd");
 		return -EINVAL;
@@ -2746,7 +2735,6 @@ static void __exit nbd_cleanup(void)
 	/* Also wait for nbd_dev_remove_work() completes */
 	destroy_workqueue(nbd_del_wq);
 
-	put_cred(nbd_cred);
 	idr_destroy(&nbd_index_idr);
 	unregister_blkdev(NBD_MAJOR, "nbd");
 }