net: ethtool: fix leaking netdev ref if ethnl_default_parse() failed

Ido spotted that I made a mistake in commit under Fixes,
ethnl_default_parse() may acquire a dev reference even when it returns
an error. This may have been driven by the code structure in dumps
(which unconditionally release dev before handling errors), but it's
too much of a trap. Functions should undo what they did before returning
an error, rather than expecting caller to clean up.

Rather than fixing ethnl_default_set_doit() directly make
ethnl_default_parse() clean up errors.

Reported-by: Ido Schimmel <[e-mail]>
Link: https://lore.kernel.org/aGEPszpq9eojNF4Y@shredder
Fixes: 963781bdfe20 ("net: ethtool: call .parse_request for SET handlers")
Reviewed-by: Ido Schimmel <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ethtool/netlink.c

···
 	if (request_ops->parse_request) {
 		ret = request_ops->parse_request(req_info, tb, info->extack);
 		if (ret < 0)
-			return ret;
+			goto err_dev;
 	}
 
 	return 0;
+
+err_dev:
+	netdev_put(req_info->dev, &req_info->dev_tracker);
+	req_info->dev = NULL;
+	return ret;
 }
 
 /**
···
 
 	ret = ethnl_default_parse(req_info, info, ops, !ops->allow_nodev_do);
 	if (ret < 0)
-		goto err_dev;
+		goto err_free;
 	ethnl_init_reply_data(reply_data, ops, req_info->dev);
 
 	rtnl_lock();
···
 		ops->cleanup_data(reply_data);
 err_dev:
 	netdev_put(req_info->dev, &req_info->dev_tracker);
+err_free:
 	kfree(reply_data);
 	kfree(req_info);
 	return ret;
···
 	}
 
 	ret = ethnl_default_parse(req_info, &info->info, ops, false);
+	if (ret < 0)
+		goto free_reply_data;
 	if (req_info->dev) {
 		/* We ignore device specification in dump requests but as the
 		 * same parser as for non-dump (doit) requests is used, it
···
 		netdev_put(req_info->dev, &req_info->dev_tracker);
 		req_info->dev = NULL;
 	}
-	if (ret < 0)
-		goto free_reply_data;
 
 	ctx->ops = ops;
 	ctx->req_info = req_info;
···
 	 * the dev's ifindex, .dumpit() will grab and release the netdev itself.
 	 */
 	ret = ethnl_default_parse(req_info, &info->info, ops, false);
+	if (ret < 0)
+		goto free_reply_data;
 	if (req_info->dev) {
 		phy_ctx->ifindex = req_info->dev->ifindex;
 		netdev_put(req_info->dev, &req_info->dev_tracker);
 		req_info->dev = NULL;
 	}
-	if (ret < 0)
-		goto free_reply_data;
 
 	ctx->ops = ops;
 	ctx->req_info = req_info;