netdev - Re: [PATCH bpf-next v7 03/10] bpf: net_sched: Add basic bpf qdisc kfuncs

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Message-ID: <CAP01T77ibGcEhwsyJb1WVaH-vhbZB_M2yVA8Uyv9b5fy=ErWQQ@mail.gmail.com>
Date: Fri, 11 Apr 2025 15:32:00 +0200
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: Amery Hung <ameryhung@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, alexei.starovoitov@...il.com, 
	andrii@...nel.org, daniel@...earbox.net, edumazet@...gle.com, kuba@...nel.org, 
	xiyou.wangcong@...il.com, jhs@...atatu.com, martin.lau@...nel.org, 
	jiri@...nulli.us, stfomichev@...il.com, toke@...hat.com, sinquersw@...il.com, 
	ekarani.silvestre@....ufcg.edu.br, yangpeihao@...u.edu.cn, 
	yepeilin.cs@...il.com, kernel-team@...a.com
Subject: Re: [PATCH bpf-next v7 03/10] bpf: net_sched: Add basic bpf qdisc kfuncs

On Wed, 9 Apr 2025 at 23:46, Amery Hung <ameryhung@...il.com> wrote:
>
> From: Amery Hung <amery.hung@...edance.com>
>
> Add basic kfuncs for working on skb in qdisc.
>
> Both bpf_qdisc_skb_drop() and bpf_kfree_skb() can be used to release
> a reference to an skb. However, bpf_qdisc_skb_drop() can only be called
> in .enqueue where a to_free skb list is available from kernel to defer
> the release. bpf_kfree_skb() should be used elsewhere. It is also used
> in bpf_obj_free_fields() when cleaning up skb in maps and collections.
>
> bpf_skb_get_hash() returns the flow hash of an skb, which can be used
> to build flow-based queueing algorithms.
>
> Finally, allow users to create read-only dynptr via bpf_dynptr_from_skb().
>
> Signed-off-by: Amery Hung <amery.hung@...edance.com>
> Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---

How do we prevent UAF when dynptr is accessed after bpf_kfree_skb?

>  [...]