[PATCH bpf-next v7 5/6] bpf: clear decap state on skb_adjust_room shrink path
flat view
COLD51d
IN BPF-NEXT: 1 (1M)
From: Nick Hudson <hidden>
Date: 2026-08-12 08:32:00
Also in:
bpf, lkml
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
1 review trailer; queued in bpf-next as ec20dee2f2c4 on 2026-08-17.
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 <redacted>
Signed-off-by: Max Tottenham <redacted>
Co-developed-by: Anna Glasgall <redacted>
Signed-off-by: Anna Glasgall <redacted>
Signed-off-by: Nick Hudson <redacted>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
net/core/filter.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index 981b75941e7f..89effff3bc52 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -3754,9 +3754,48 @@ 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