There's a consistent pattern where the .cleanup_data() callback is
called when .prepare_data() fails, when it should really be called to
clean after a successfull .prepare_data() as per the documentation.

Rewrite the error-handling paths to make sure we don't cleanup
un-prepared data.

Fixes: 728480f12442 ("ethtool: default handlers for GET requests")
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 net/ethtool/netlink.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index a163d40c6431..977beeaaa2f9 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -500,7 +500,7 @@ static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
 		netdev_unlock_ops(req_info->dev);
 	rtnl_unlock();
 	if (ret < 0)
-		goto err_cleanup;
+		goto err_dev;
 	ret = ops->reply_size(req_info, reply_data);
 	if (ret < 0)
 		goto err_cleanup;
@@ -560,7 +560,7 @@ static int ethnl_default_dump_one(struct sk_buff *skb, struct net_device *dev,
 	netdev_unlock_ops(dev);
 	rtnl_unlock();
 	if (ret < 0)
-		goto out;
+		goto out_cancel;
 	ret = ethnl_fill_reply_header(skb, dev, ctx->ops->hdr_attr);
 	if (ret < 0)
 		goto out;
@@ -569,6 +569,7 @@ static int ethnl_default_dump_one(struct sk_buff *skb, struct net_device *dev,
 out:
 	if (ctx->ops->cleanup_data)
 		ctx->ops->cleanup_data(ctx->reply_data);
+out_cancel:
 	ctx->reply_data->dev = NULL;
 	if (ret < 0)
 		genlmsg_cancel(skb, ehdr);
@@ -793,7 +794,7 @@ static void ethnl_default_notify(struct net_device *dev, unsigned int cmd,
 	ethnl_init_reply_data(reply_data, ops, dev);
 	ret = ops->prepare_data(req_info, reply_data, &info);
 	if (ret < 0)
-		goto err_cleanup;
+		goto err_rep;
 	ret = ops->reply_size(req_info, reply_data);
 	if (ret < 0)
 		goto err_cleanup;
@@ -828,6 +829,7 @@ static void ethnl_default_notify(struct net_device *dev, unsigned int cmd,
 err_cleanup:
 	if (ops->cleanup_data)
 		ops->cleanup_data(reply_data);
+err_rep:
 	kfree(reply_data);
 	kfree(req_info);
 	return;
-- 
2.49.0

On Thu, Apr 03, 2025 at 03:24:46PM +0200, Maxime Chevallier wrote:
> There's a consistent pattern where the .cleanup_data() callback is
> called when .prepare_data() fails, when it should really be called to
> clean after a successfull .prepare_data() as per the documentation.

Nit, if you have to respin for some other reason: successful

> 
> Rewrite the error-handling paths to make sure we don't cleanup
> un-prepared data.
> 
> Fixes: 728480f12442 ("ethtool: default handlers for GET requests")
> Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

I agree this makes sense and addresses all instances
of this problem in this file.

Reviewed-by: Simon Horman <horms@kernel.org>