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[34.85.134.180]) by smtp.gmail.com with UTF8SMTPSA id 956f58d0204a3-64e91bb9344sm2236439d50.12.2026.03.18.13.09.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Mar 2026 13:09:29 -0700 (PDT) Date: Wed, 18 Mar 2026 16:09:28 -0400 From: Willem de Bruijn To: Nick Hudson , bpf@vger.kernel.org, netdev@vger.kernel.org Cc: Willem de Bruijn , Nick Hudson , Max Tottenham , Anna Glasgall , Martin KaFai Lau , Daniel Borkmann , Alexei Starovoitov , Andrii Nakryiko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org Message-ID: In-Reply-To: <20260318134242.2725749-6-nhudson@akamai.com> References: <20260318134242.2725749-1-nhudson@akamai.com> <20260318134242.2725749-6-nhudson@akamai.com> Subject: Re: [PATCH v2 5/5] bpf: clear decap tunnel GSO state in skb_adjust_room Precedence: bulk X-Mailing-List: netdev@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} > - 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. > > 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 | 31 +++++++++++++++++++++++++++++++ > 1 file changed, 31 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 47aec44a9cd3..35af1199ab97 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -3665,6 +3665,37 @@ 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_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))) > + if (skb->encapsulation) > + skb->encapsulation = 0; Is there any chance that this might clear it while some other tunnel is still active? From a quick grep on skb->encapsulation the only possible hit I see is SKB_GSO_ESP. > + } > + > /* Header must be checked, and gso_segs recomputed. */ > shinfo->gso_type |= SKB_GSO_DODGY; > shinfo->gso_segs = 0; > -- > 2.34.1 >