Re: [PATCH v2 5/5] bpf: clear decap tunnel GSO state in skb_adjust_room
From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2026-03-18 20:09:30
Also in:
bpf, lkml
Nick Hudson wrote:
quoted hunk ↗ jump to hunk
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 <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> --- 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