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[34.85.165.172]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7a36e42ff26sm89073237b3.9.2026.04.08.08.10.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2026 08:10:27 -0700 (PDT) Date: Wed, 08 Apr 2026 11:10:25 -0400 From: Willem de Bruijn To: Nick Hudson , bpf@vger.kernel.org, netdev@vger.kernel.org, Willem de Bruijn , Martin KaFai Lau Cc: Nick Hudson , Max Tottenham , Anna Glasgall , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org Message-ID: In-Reply-To: <20260407105005.1639815-6-nhudson@akamai.com> References: <20260407105005.1639815-1-nhudson@akamai.com> <20260407105005.1639815-6-nhudson@akamai.com> Subject: Re: [PATCH bpf-next v3 5/6] bpf: clear decap tunnel GSO state in skb_adjust_room Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit 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}, and > SKB_GSO_TUNNEL_REMCSUM > - 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 and GSO state removed then reset encap_hdr_csum, and > remcsum_offload. > > Co-developed-by: Max Tottenham > Signed-off-by: Max Tottenham > Co-developed-by: Anna Glasgall > Signed-off-by: Anna Glasgall > Signed-off-by: Nick Hudson > --- > net/core/filter.c | 40 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 40 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 7f8d43420afb..04059d07d368 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -3667,6 +3667,46 @@ 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 | > + SKB_GSO_TUNNEL_REMCSUM))) > + shinfo->gso_type &= ~(SKB_GSO_UDP_TUNNEL | > + SKB_GSO_UDP_TUNNEL_CSUM | > + SKB_GSO_TUNNEL_REMCSUM); REMCSUM was previously not included in the series. It is a non-obvious and rare enough feature that I would exclude it, or move it to a separate patch. > + 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 = !!(shinfo->gso_type & SKB_GSO_UDP_TUNNEL_CSUM); Since the flag is never set, only possibly cleared: just clear this field when clearing the flag? It appears that this is only used for deprecated UFO anyway. > + skb->remcsum_offload = !!(shinfo->gso_type & SKB_GSO_TUNNEL_REMCSUM); Always zero?