> I think you prefer like this:
Yes, this looks good to me. A few comments inline.
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2644,6 +2644,11 @@ union bpf_attr {
> * Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the
> * L2 type as Ethernet.
> *
> + * * **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**,
> + * **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**:
> + * Indicates the new IP header version after decapsulate the
> + * outer IP header.
> + *
> * A call to this helper is susceptible to change the underlying
> * packet buffer. Therefore, at load time, all checks on pointers
> * previously done by the verifier are invalidated and must be
> @@ -5803,6 +5808,8 @@ enum {
> BPF_F_ADJ_ROOM_ENCAP_L4_UDP = (1ULL << 4),
> BPF_F_ADJ_ROOM_NO_CSUM_RESET = (1ULL << 5),
> BPF_F_ADJ_ROOM_ENCAP_L2_ETH = (1ULL << 6),
> + BPF_F_ADJ_ROOM_DECAP_L3_IPV4 = (1ULL << 7),
> + BPF_F_ADJ_ROOM_DECAP_L3_IPV6 = (1ULL << 8),
> };
>
> enum {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 43cc1fe58a2c..0bbe5e67337c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3381,13 +3381,17 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb)
> #define BPF_F_ADJ_ROOM_ENCAP_L3_MASK (BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 | \
> BPF_F_ADJ_ROOM_ENCAP_L3_IPV6)
>
> +#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_MASK (BPF_F_ADJ_ROOM_FIXED_GSO | \
> BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \
> BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \
> BPF_F_ADJ_ROOM_ENCAP_L4_UDP | \
> BPF_F_ADJ_ROOM_ENCAP_L2_ETH | \
> BPF_F_ADJ_ROOM_ENCAP_L2( \
> - BPF_ADJ_ROOM_ENCAP_L2_MASK))
> + BPF_ADJ_ROOM_ENCAP_L2_MASK) | \
> + BPF_F_ADJ_ROOM_DECAP_L3_MASK)
>
> static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> u64 flags)
> @@ -3501,6 +3505,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> int ret;
>
> if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO |
> + BPF_F_ADJ_ROOM_DECAP_L3_MASK |
> BPF_F_ADJ_ROOM_NO_CSUM_RESET)))
> return -EINVAL;
>
> @@ -3519,6 +3524,14 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> if (unlikely(ret < 0))
> return ret;
>
> + /* Match skb->protocol to new outer l3 protocol */
> + if (skb->protocol == htons(ETH_P_IP) &&
> + flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV6)
> + skb->protocol = htons(ETH_P_IPV6);
> + else if (skb->protocol == htons(ETH_P_IPV6) &&
> + flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV4)
> + skb->protocol = htons(ETH_P_IP);
> +
> if (skb_is_gso(skb)) {
> struct skb_shared_info *shinfo = skb_shinfo(skb);
>
> @@ -3597,6 +3610,10 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> proto != htons(ETH_P_IPV6)))
> return -ENOTSUPP;
>
> + if (unlikely(shrink && flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV4 &&
> + flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV6))
> + return -EINVAL;
> +
parentheses and can use mask:
if (shrink && (flags & .._MASK == .._MASK)
also should fail if the flags are passed but shrink is false.
> off = skb_mac_header_len(skb);
> switch (mode) {
> case BPF_ADJ_ROOM_NET:
> @@ -3608,6 +3625,16 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> return -ENOTSUPP;
> }
>
> + if (shrink) {
> + if (proto == htons(ETH_P_IP) &&
> + flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV6) {
> + len_min = sizeof(struct ipv6hdr);
> + } else if (proto == htons(ETH_P_IPV6) &&
> + flags & BPF_F_ADJ_ROOM_DECAP_L3_IPV4) {
> + len_min = sizeof(struct iphdr);
> + }
> + }
> +
No need to test proto first?
> len_cur = skb->len - skb_network_offset(skb);
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 464ca3f01fe7..041361bc6ccf 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -2644,6 +2644,11 @@ union bpf_attr {
> * Use with BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the
> * L2 type as Ethernet.
> *
> + * * **BPF_F_ADJ_ROOM_DECAP_L3_IPV4**,
> + * **BPF_F_ADJ_ROOM_DECAP_L3_IPV6**:
> + * Indicates the new IP header version after decapsulate the
> + * outer IP header.
> + *
> * A call to this helper is susceptible to change the underlying
> * packet buffer. Therefore, at load time, all checks on pointers
> * previously done by the verifier are invalidated and must be
> @@ -5803,6 +5808,8 @@ enum {
> BPF_F_ADJ_ROOM_ENCAP_L4_UDP = (1ULL << 4),
> BPF_F_ADJ_ROOM_NO_CSUM_RESET = (1ULL << 5),
> BPF_F_ADJ_ROOM_ENCAP_L2_ETH = (1ULL << 6),
> + BPF_F_ADJ_ROOM_DECAP_L3_IPV4 = (1ULL << 7),
> + BPF_F_ADJ_ROOM_DECAP_L3_IPV6 = (1ULL << 8),
> };
>
> enum {
>
