linux-kernel - Re: [PATCH bpf] xsk: fix init race causing NPD/UAF in xsk

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Message-Id: <33188e4423c52e3db72a6897e721674d8a9cb45534640e4999e906d1c4d948fa@mail.kernel.org>
Date: Thu,  8 Jan 2026 11:53:06 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: qikeyu2017@...il.com,bpf@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,bjorn@...nel.org,hawk@...nel.org,pabeni@...hat.com,magnus.karlsson@...el.com,daniel@...earbox.net,maciej.fijalkowski@...el.com,kuba@...nel.org,edumazet@...gle.com,horms@...nel.org,ast@...nel.org,sdf@...ichev.me,john.fastabend@...il.com,qikeyu2017@...il.com,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf] xsk: fix init race causing NPD/UAF in xsk_create()

> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index f093c3453f64..63b48e4b8b65 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -1942,16 +1938,20 @@ static int __init xsk_init(void)
>  		goto out_unreg_notif;
>  	}
>
> +	err = sock_register(&xsk_family_ops);
> +	if (err)
> +		goto out_proto;

If sock_register() fails here, does xsk_tx_generic_cache get leaked?
The kmem_cache was successfully created just above this, but the error
path at out_proto does not appear to call kmem_cache_destroy().

Looking at the error unwind below:

> +
>  	return 0;
>
>  out_unreg_notif:
>  	unregister_netdevice_notifier(&xsk_netdev_notifier);
>  out_pernet:
>  	unregister_pernet_subsys(&xsk_net_ops);
> -out_sk:
> -	sock_unregister(PF_XDP);
>  out_proto:
>  	proto_unregister(&xsk_proto);

The path from sock_register() failure goes to out_proto, which only calls
proto_unregister() before falling through. There is no kmem_cache_destroy()
for xsk_tx_generic_cache in this error path.

Should there be a new label between out_unreg_notif and out_pernet that
destroys the kmem_cache, and should out_proto jump there instead?


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/20815690741