From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Nick Hudson <nhudson@akamai.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org,
Willem de Bruijn <willemb@google.com>,
Martin KaFai Lau <martin.lau@linux.dev>
Cc: Nick Hudson <nhudson@akamai.com>,
Max Tottenham <mtottenh@akamai.com>,
Anna Glasgall <aglasgal@akamai.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v4 5/6] bpf: clear decap tunnel GSO state in skb_adjust_room
Date: Thu, 16 Apr 2026 08:32:13 -0400 [thread overview]
Message-ID: <willemdebruijn.kernel.30d031033dc61@gmail.com> (raw)
In-Reply-To: <20260416075514.927101-6-nhudson@akamai.com>
Nick Hudson wrote:
> On shrink in bpf_skb_adjust_room(), clear tunnel-specific GSO flags
> according to the decapsulation flags:
>
> - BPF_F_ADJ_ROOM_DECAP_L4_UDP clears SKB_GSO_UDP_TUNNEL{,_CSUM}
> - BPF_F_ADJ_ROOM_DECAP_L4_GRE clears SKB_GSO_GRE{,_CSUM}
> - BPF_F_ADJ_ROOM_DECAP_IPXIP4 clears SKB_GSO_IPXIP4
> - BPF_F_ADJ_ROOM_DECAP_IPXIP6 clears SKB_GSO_IPXIP6
>
> When all tunnel-related GSO bits are cleared, also clear
> skb->encapsulation.
>
> Handle the ESP inside a UDP tunnel case where encapsulation should remain
> set.
>
> If UDP decap is performed, clear encap_hdr_csum and remcsum_offload.
>
> Co-developed-by: Max Tottenham <mtottenh@akamai.com>
> Signed-off-by: Max Tottenham <mtottenh@akamai.com>
> Co-developed-by: Anna Glasgall <aglasgal@akamai.com>
> Signed-off-by: Anna Glasgall <aglasgal@akamai.com>
> Signed-off-by: Nick Hudson <nhudson@akamai.com>
> ---
> net/core/filter.c | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 7f8d43420afb..e113ae2f3f14 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3667,6 +3667,44 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
> skb_increase_gso_size(shinfo, len_diff);
>
> + /* Selective GSO flag clearing based on decap type.
> + * Only clear the flags for the tunnel layer being removed.
> + */
> + 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;
> +
> + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_UDP) {
> + skb->encap_hdr_csum = 0;
This field is not used with UDP_L4.
Similar to remcsum, I'd ignore it entirely in this series.
> + skb->remcsum_offload = 0;
Why still include remote checksum handling?
> + }
> + }
> +
> /* Header must be checked, and gso_segs recomputed. */
> shinfo->gso_type |= SKB_GSO_DODGY;
> shinfo->gso_segs = 0;
> --
> 2.34.1
>
next prev parent reply other threads:[~2026-04-16 12:32 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260416075514.927101-1-nhudson@akamai.com>
2026-04-16 7:55 ` [PATCH bpf-next v4 1/6] bpf: name the enum for BPF_FUNC_skb_adjust_room flags Nick Hudson
2026-04-16 7:55 ` [PATCH bpf-next v4 2/6] bpf: refactor masks for ADJ_ROOM flags and encap validation Nick Hudson
2026-04-16 7:55 ` [PATCH bpf-next v4 3/6] bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation Nick Hudson
2026-04-16 7:55 ` [PATCH bpf-next v4 4/6] bpf: allow new DECAP flags and add guard rails Nick Hudson
2026-04-16 7:55 ` [PATCH bpf-next v4 5/6] bpf: clear decap tunnel GSO state in skb_adjust_room Nick Hudson
2026-04-16 8:34 ` bot+bpf-ci
2026-04-16 12:32 ` Willem de Bruijn [this message]
2026-04-17 12:27 ` Hudson, Nick
2026-04-16 7:55 ` [PATCH bpf-next v4 6/6] selftests/bpf: tc_tunnel validate decap GSO state Nick Hudson
2026-04-16 12:33 ` Willem de Bruijn
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