Subject: Re: [PATCH] netfilter: nf_tables: fix use-after-free on ops->dev

From: Pablo Neira Ayuso <[email-masked]>
Date: Tue, 3 Mar 2026 00:08:56 +0100

On Mon, Mar 02, 2026 at 06:26:05PM -0300, Helen Koike wrote:
> struct nf_hook_ops has a pointer to dev, which can be used by
> __nf_unregister_net_hook() after it has been freed by tun_chr_close().
> 
> Fix it  by calling dev_hold() when saving dev to ops struct.

Sorry, I don't think this patch works, dev_hold()/dev_put() use
per_cpu area.

The nf_tables_flowtable_event() function used to release the hook, but
now things have changed since there is auto-hook registration.

> Reported-by: [email-masked]
> Closes: https://syzkaller.appspot.com/bug?extid=bb9127e278fa198e110c
> Signed-off-by: Helen Koike <[email-masked]>
> ---
>  net/netfilter/nf_tables_api.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> index fd7f7e4e2a43..00b5f900a51d 100644
> --- a/net/netfilter/nf_tables_api.c
> +++ b/net/netfilter/nf_tables_api.c
> @@ -352,6 +352,7 @@ static void nft_netdev_hook_free_ops(struct nft_hook *hook)
>  
>  	list_for_each_entry_safe(ops, next, &hook->ops_list, list) {
>  		list_del(&ops->list);
> +		dev_put(ops->dev);
>  		kfree(ops);
>  	}
>  }
> @@ -2374,6 +2375,7 @@ static struct nft_hook *nft_netdev_hook_alloc(struct net *net,
>  			err = -ENOMEM;
>  			goto err_hook_free;
>  		}
> +		dev_hold(dev);
>  		ops->dev = dev;
>  		list_add_tail(&ops->list, &hook->ops_list);
>  	}
> -- 
> 2.53.0
>