netdev - Re: [PATCH bpf-next v5 09/13] bpf: net_sched: Disable attaching bpf qdisc to non root

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Message-ID: <CAADnVQJ-kSNw4hiZ5p_fpsVAyYWDSu50OJyY_NGmaxk9+ofiiQ@mail.gmail.com>
Date: Fri, 14 Mar 2025 13:31:38 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Amery Hung <ameryhung@...il.com>
Cc: Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Jakub Kicinski <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Cong Wang <xiyou.wangcong@...il.com>, 
	Jamal Hadi Salim <jhs@...atatu.com>, Kui-Feng Lee <sinquersw@...il.com>, 
	Toke Høiland-Jørgensen <toke@...hat.com>, 
	Jiri Pirko <jiri@...nulli.us>, Stanislav Fomichev <stfomichev@...il.com>, 
	ekarani.silvestre@....ufcg.edu.br, yangpeihao@...u.edu.cn, 
	Peilin Ye <yepeilin.cs@...il.com>, Kernel Team <kernel-team@...a.com>
Subject: Re: [PATCH bpf-next v5 09/13] bpf: net_sched: Disable attaching bpf
 qdisc to non root

On Thu, Mar 13, 2025 at 12:03 PM Amery Hung <ameryhung@...il.com> wrote:
>
> Do not allow users to attach bpf qdiscs to classful qdiscs. This is to
> prevent accidentally breaking existings classful qdiscs if they rely on
> some data in the child qdisc. This restriction can potentially be lifted
> in the future. Note that, we still allow bpf qdisc to be attached to mq.
>
> Signed-off-by: Amery Hung <ameryhung@...il.com>
> ---
>  net/sched/bpf_qdisc.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/net/sched/bpf_qdisc.c b/net/sched/bpf_qdisc.c
> index e4e7a5879869..c2f33cd35674 100644
> --- a/net/sched/bpf_qdisc.c
> +++ b/net/sched/bpf_qdisc.c
> @@ -170,8 +170,11 @@ static int bpf_qdisc_gen_prologue(struct bpf_insn *insn_buf, bool direct_write,
>                 return 0;
>
>         *insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
> +       *insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1, 16);
>         *insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 0);

Both loads need a comment.
It's st_ops callback specific and not obvious what ends up in r1 and r2.

>         *insn++ = BPF_CALL_KFUNC(0, bpf_qdisc_init_prologue_ids[0]);
> +       *insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1);
> +       *insn++ = BPF_EXIT_INSN();
>         *insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_6);
>         *insn++ = prog->insnsi[0];
>
> @@ -239,11 +242,26 @@ __bpf_kfunc void bpf_qdisc_watchdog_schedule(struct Qdisc *sch, u64 expire, u64
>  }
>
>  /* bpf_qdisc_init_prologue - Hidden kfunc called in prologue of .init. */
> -__bpf_kfunc void bpf_qdisc_init_prologue(struct Qdisc *sch)
> +__bpf_kfunc int bpf_qdisc_init_prologue(struct Qdisc *sch,
> +                                       struct netlink_ext_ack *extack)
>  {
>         struct bpf_sched_data *q = qdisc_priv(sch);
> +       struct net_device *dev = qdisc_dev(sch);
> +       struct Qdisc *p;
> +
> +       if (sch->parent != TC_H_ROOT) {
> +               p = qdisc_lookup(dev, TC_H_MAJ(sch->parent));
> +               if (!p)
> +                       return -ENOENT;
> +
> +               if (!(p->flags & TCQ_F_MQROOT)) {
> +                       NL_SET_ERR_MSG(extack, "BPF qdisc only supported on root or mq");
> +                       return -EINVAL;
> +               }
> +       }
>
>         qdisc_watchdog_init(&q->watchdog, sch);
> +       return 0;
>  }
>
>  /* bpf_qdisc_reset_destroy_epilogue - Hidden kfunc called in epilogue of .reset
> --
> 2.47.1
>