From: Martin KaFai Lau <martin.lau@linux.dev>
To: nhudson@akamai.com
Cc: bot+bpf-ci@kernel.org, bpf@vger.kernel.org,
netdev@vger.kernel.org, willemb@google.com, mtottenh@akamai.com,
aglasgal@akamai.com, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com,
davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
pabeni@redhat.com, linux-kernel@vger.kernel.org,
martin.lau@kernel.org, yonghong.song@linux.dev, clm@meta.com,
ihor.solodrai@linux.dev
Subject: Re: [PATCH v5 5/6] bpf: clear decap tunnel GSO state in skb_adjust_room
Date: Mon, 27 Apr 2026 15:19:53 -0700 [thread overview]
Message-ID: <2026427201356.-eYM.martin.lau@linux.dev> (raw)
In-Reply-To: <82df2b6834553e3f2da26e5ee1f1b880f8a1af073e6fd88894a4839c66b7b121@mail.kernel.org>
On Mon, Apr 20, 2026 at 11:19:31AM +0000, bot+bpf-ci@kernel.org wrote:
> > + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_UDP) &&
> > + (shinfo->gso_type & (SKB_GSO_UDP_TUNNEL |
> > + SKB_GSO_UDP_TUNNEL_CSUM)))
> > + shinfo->gso_type &= ~(SKB_GSO_UDP_TUNNEL |
> > + SKB_GSO_UDP_TUNNEL_CSUM);
> > + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_GRE) &&
> > + (shinfo->gso_type & (SKB_GSO_GRE | SKB_GSO_GRE_CSUM)))
> > + shinfo->gso_type &= ~(SKB_GSO_GRE |
> > + SKB_GSO_GRE_CSUM);
> > + if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP4) &&
> > + (shinfo->gso_type & SKB_GSO_IPXIP4))
> > + shinfo->gso_type &= ~SKB_GSO_IPXIP4;
> > + if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP6) &&
> > + (shinfo->gso_type & SKB_GSO_IPXIP6))
> > + shinfo->gso_type &= ~SKB_GSO_IPXIP6;
> > +
> > + /* Clear encapsulation flag only when no tunnel GSO flags remain */
> > + if (flags & (BPF_F_ADJ_ROOM_DECAP_L4_MASK |
> > + BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK)) {
> > + if (!(shinfo->gso_type & (SKB_GSO_UDP_TUNNEL |
> > + SKB_GSO_UDP_TUNNEL_CSUM |
> > + SKB_GSO_GRE |
> > + SKB_GSO_GRE_CSUM |
> > + SKB_GSO_IPXIP4 |
> > + SKB_GSO_IPXIP6 |
> > + SKB_GSO_ESP)))
> > + if (skb->encapsulation)
> > + skb->encapsulation = 0;
> > + }
>
> All of this new GSO flag clearing logic is added inside the if (skb_is_gso(skb))
> block in bpf_skb_net_shrink(). Does this mean non-GSO packets bypass the
> decapsulation state clearing?
>
> BPF programs can call bpf_skb_adjust_room() to decapsulate non-GSO packets
> as well. If a non-GSO packet undergoes decapsulation with the tunnel headers
> stripped, but skb->encapsulation remains set, could this cause downstream
> network stack components to misinterpret the packet as still being
> encapsulated?
It has been asked multiple times by different AI review agents but has been
ignored afaik. Please reply/address it so they won't reiterate. From
a quick look, bpf_skb_net_grow() sets the encapsulation regardless
of skb_is_gso.
next prev parent reply other threads:[~2026-04-27 22:20 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-20 10:40 [PATCH bpf-next v5 0/6] bpf: decap flags and GSO state updates Nick Hudson
2026-04-20 10:40 ` [PATCH v5 1/6] bpf: name the enum for BPF_FUNC_skb_adjust_room flags Nick Hudson
2026-04-20 10:40 ` [PATCH v5 2/6] bpf: refactor masks for ADJ_ROOM flags and encap validation Nick Hudson
2026-04-20 19:42 ` Willem de Bruijn
2026-04-27 22:40 ` Martin KaFai Lau
2026-04-20 10:40 ` [PATCH v5 3/6] bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation Nick Hudson
2026-04-20 19:44 ` Willem de Bruijn
2026-04-20 10:40 ` [PATCH v5 4/6] bpf: allow new DECAP flags and add guard rails Nick Hudson
2026-04-20 19:45 ` Willem de Bruijn
2026-04-20 10:40 ` [PATCH v5 5/6] bpf: clear decap tunnel GSO state in skb_adjust_room Nick Hudson
2026-04-20 11:19 ` bot+bpf-ci
2026-04-27 22:19 ` Martin KaFai Lau [this message]
2026-04-20 19:46 ` Willem de Bruijn
2026-04-20 10:40 ` [PATCH v5 6/6] selftests/bpf: tc_tunnel validate decap GSO state Nick Hudson
2026-04-20 11:19 ` bot+bpf-ci
2026-04-27 22:36 ` Martin KaFai Lau
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