[PATCH bpf-next v7 4/6] bpf: allow new DECAP flags and add guard rails
From: Nick Hudson <hidden>
Date: 2026-08-12 08:31:59
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
Add checks to require shrink-only decap, reject conflicting decap flag combinations, and verify removed length is sufficient for claimed header decapsulation. 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 | 44 +++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 43 insertions(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 89e516049c85..981b75941e7f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -56,6 +56,7 @@ #include <net/sock_reuseport.h> #include <net/busy_poll.h> #include <net/tcp.h> +#include <net/gre.h> #include <net/xfrm.h> #include <net/udp.h> #include <linux/bpf_trace.h>
@@ -3572,6 +3573,12 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb) #define BPF_F_ADJ_ROOM_DECAP_L3_MASK (BPF_F_ADJ_ROOM_DECAP_L3_IPV4 | \ BPF_F_ADJ_ROOM_DECAP_L3_IPV6) +#define BPF_F_ADJ_ROOM_DECAP_L4_MASK (BPF_F_ADJ_ROOM_DECAP_L4_UDP | \ + BPF_F_ADJ_ROOM_DECAP_L4_GRE) + +#define BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK (BPF_F_ADJ_ROOM_DECAP_IPXIP4 | \ + BPF_F_ADJ_ROOM_DECAP_IPXIP6) + #define BPF_F_ADJ_ROOM_ENCAP_MASK (BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \ BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \ BPF_F_ADJ_ROOM_ENCAP_L4_UDP | \
@@ -3579,7 +3586,9 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb) BPF_F_ADJ_ROOM_ENCAP_L2( \ BPF_ADJ_ROOM_ENCAP_L2_MASK)) -#define BPF_F_ADJ_ROOM_DECAP_MASK (BPF_F_ADJ_ROOM_DECAP_L3_MASK) +#define BPF_F_ADJ_ROOM_DECAP_MASK (BPF_F_ADJ_ROOM_DECAP_L3_MASK | \ + BPF_F_ADJ_ROOM_DECAP_L4_MASK | \ + BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) #define BPF_F_ADJ_ROOM_MASK (BPF_F_ADJ_ROOM_FIXED_GSO | \ BPF_F_ADJ_ROOM_ENCAP_MASK | \
@@ -3827,6 +3836,8 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, } if (flags & BPF_F_ADJ_ROOM_DECAP_MASK) { + u32 len_decap_min = 0; + if (!shrink) return -EINVAL;
@@ -3835,6 +3846,37 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, BPF_F_ADJ_ROOM_DECAP_L3_MASK) return -EINVAL; + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_MASK) == + BPF_F_ADJ_ROOM_DECAP_L4_MASK) + return -EINVAL; + + if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) == + BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK) + return -EINVAL; + + /* Reject mutually exclusive decap tunnel type flags. */ + if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_MASK) && + (flags & BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK)) + return -EINVAL; + + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_MASK) + len_decap_min += bpf_skb_net_base_len(skb); + + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_UDP) + len_decap_min += sizeof(struct udphdr); + + if (flags & BPF_F_ADJ_ROOM_DECAP_L4_GRE) + len_decap_min += sizeof(struct gre_base_hdr); + + if (flags & BPF_F_ADJ_ROOM_DECAP_IPXIP4) + len_decap_min += sizeof(struct iphdr); + + if (flags & BPF_F_ADJ_ROOM_DECAP_IPXIP6) + len_decap_min += sizeof(struct ipv6hdr); + + if (len_diff_abs < len_decap_min) + return -EINVAL; + if (flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV4) len_min = sizeof(struct iphdr);
--
2.34.1