Subject: Re: [RFC PATCH net-next 02/12] devlink: Hold a reference on parent device

From: Jiri Pirko <[email-masked]>
Date: Tue, 17 Oct 2023 09:56:18 +0200

Tue, Oct 17, 2023 at 09:42:47AM CEST, [email-masked] wrote:
>Each devlink instance is associated with a parent device and a pointer
>to this device is stored in the devlink structure, but devlink does not
>hold a reference on this device.
>
>This is going to be a problem in the next patch where - among other
>things - devlink will acquire the device lock during netns dismantle,
>before the reload operation. Since netns dismantle is performed
>asynchronously and since a reference is not held on the parent device,
>it will be possible to hit a use-after-free.
>
>Prepare for the upcoming change by holding a reference on the parent
>device.
>

Just a note, I'm currently pushing the same patch as a part
of my patchset:
https://lore.kernel.org/all/[email-masked]/

>Signed-off-by: Ido Schimmel <[email-masked]>
>Reviewed-by: Jiri Pirko <[email-masked]>
>---
> net/devlink/core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/net/devlink/core.c b/net/devlink/core.c
>index bcbbb952569f..5b8b692b8c76 100644
>--- a/net/devlink/core.c
>+++ b/net/devlink/core.c
>@@ -4,6 +4,7 @@
>  * Copyright (c) 2016 Jiri Pirko <[email-masked]>
>  */
> 
>+#include <linux/device.h>
> #include <net/genetlink.h>
> #define CREATE_TRACE_POINTS
> #include <trace/events/devlink.h>
>@@ -310,6 +311,7 @@ static void devlink_release(struct work_struct *work)
> 
> 	mutex_destroy(&devlink->lock);
> 	lockdep_unregister_key(&devlink->lock_key);
>+	put_device(devlink->dev);
> 	kfree(devlink);
> }
> 
>@@ -425,6 +427,7 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
> 	if (ret < 0)
> 		goto err_xa_alloc;
> 
>+	get_device(dev);
> 	devlink->dev = dev;

Nit:
	devlink->dev = get_device(dev);

> 	devlink->ops = ops;
> 	xa_init_flags(&devlink->ports, XA_FLAGS_ALLOC);
>-- 
>2.40.1
>
>