From: Nick Hudson <nhudson@akamai.com>
To: 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: [PATCH v6 5/6] bpf: clear decap state on skb_adjust_room shrink path
Date: Mon, 4 May 2026 11:17:58 +0100 [thread overview]
Message-ID: <20260504101759.3319427-6-nhudson@akamai.com> (raw)
In-Reply-To: <20260504101759.3319427-1-nhudson@akamai.com>
On shrink in bpf_skb_adjust_room(), apply decapsulation state updates
according to BPF_F_ADJ_ROOM_DECAP_* flags.
For GSO skbs, clear only the tunnel gso_type bits that correspond to the
requested decap layer:
- DECAP_L4_UDP: SKB_GSO_UDP_TUNNEL{,_CSUM}
- DECAP_L4_GRE: SKB_GSO_GRE{,_CSUM}
- DECAP_IPXIP4: SKB_GSO_IPXIP4
- DECAP_IPXIP6: SKB_GSO_IPXIP6
Then clear skb->encapsulation only if no tunnel GSO bits remain, keeping
encapsulation set for cases such as ESP-in-UDP where tunnel state remains.
For non-GSO skbs, there are no tunnel GSO bits to consult, so clear
skb->encapsulation directly when DECAP_L4_* or DECAP_IPXIP_* flags are set.
This keeps decap state handling consistent between GSO and non-GSO packets.
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 | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index 185a11f425fa..3213732dff84 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3666,9 +3666,48 @@ 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;
+ }
+
/* Header must be checked, and gso_segs recomputed. */
shinfo->gso_type |= SKB_GSO_DODGY;
shinfo->gso_segs = 0;
+ } else {
+ /* For non-GSO packets, clear encapsulation if decap flags are set */
+ if ((flags & (BPF_F_ADJ_ROOM_DECAP_L4_MASK |
+ BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK)) &&
+ skb->encapsulation)
+ skb->encapsulation = 0;
}
return 0;
--
2.34.1
next prev parent reply other threads:[~2026-05-04 10:19 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-04 10:17 [PATCH bpf-next v6 0/6] bpf: decap flags and GSO state updates Nick Hudson
2026-05-04 10:17 ` [PATCH v6 1/6] bpf: name the enum for BPF_FUNC_skb_adjust_room flags Nick Hudson
2026-05-04 11:03 ` bot+bpf-ci
2026-05-04 10:17 ` [PATCH v6 2/6] bpf: refactor masks for ADJ_ROOM flags and encap validation Nick Hudson
2026-05-04 11:03 ` bot+bpf-ci
2026-05-04 17:14 ` Willem de Bruijn
2026-05-04 10:17 ` [PATCH v6 3/6] bpf: add BPF_F_ADJ_ROOM_DECAP_* flags for tunnel decapsulation Nick Hudson
2026-05-04 11:03 ` bot+bpf-ci
2026-05-04 10:17 ` [PATCH v6 4/6] bpf: allow new DECAP flags and add guard rails Nick Hudson
2026-05-04 10:17 ` Nick Hudson [this message]
2026-05-04 17:15 ` [PATCH v6 5/6] bpf: clear decap state on skb_adjust_room shrink path Willem de Bruijn
2026-05-04 10:17 ` [PATCH v6 6/6] selftests/bpf: tc_tunnel - validate decap GSO and encapsulation state Nick Hudson
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