netdev - Re: [PATCH net/bpf] bpf: add bpf_prog_run_data

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Message-ID: <CA+NMeC9WciDGe0hfNTSZsjbHDbO_SyFG3+cO0hHEc5dUyw5tTw@mail.gmail.com>
Date: Thu, 13 Nov 2025 13:18:03 -0300
From: Victor Nogueira <victor@...atatu.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	bpf@...r.kernel.org, Simon Horman <horms@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	Toke Høiland-Jørgensen <toke@...hat.com>, 
	eric.dumazet@...il.com, syzbot <syzkaller@...glegroups.com>, 
	Paul Blakey <paulb@...dia.com>
Subject: Re: [PATCH net/bpf] bpf: add bpf_prog_run_data_pointers()

On Wed, Nov 12, 2025 at 9:55 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> syzbot found that cls_bpf_classify() is able to change
> tc_skb_cb(skb)->drop_reason triggering a warning in sk_skb_reason_drop().
>
> WARNING: CPU: 0 PID: 5965 at net/core/skbuff.c:1192 __sk_skb_reason_drop net/core/skbuff.c:1189 [inline]
> WARNING: CPU: 0 PID: 5965 at net/core/skbuff.c:1192 sk_skb_reason_drop+0x76/0x170 net/core/skbuff.c:1214
>
> struct tc_skb_cb has been added in commit ec624fe740b4 ("net/sched:
> Extend qdisc control block with tc control block"), which added a wrong
> interaction with db58ba459202 ("bpf: wire in data and data_end for
> cls_act_bpf").
>
> drop_reason was added later.
>
> Add bpf_prog_run_data_pointers() helper to save/restore the net_sched
> storage colliding with BPF data_meta/data_end.
>
> Fixes: ec624fe740b4 ("net/sched: Extend qdisc control block with tc control block")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Closes: https://lore.kernel.org/netdev/6913437c.a70a0220.22f260.013b.GAE@google.com/
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Paul Blakey <paulb@...dia.com>

Reviewed-by: Victor Nogueira <victor@...atatu.com>

Thanks!