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Message-ID: <CA+FuTSeE-S9_Uc6Cqs=EqYZd-K6kj=Ex4sudNx7u8HMLcrereQ@mail.gmail.com>
Date: Mon, 9 Jan 2023 08:32:05 -0500
From: Willem de Bruijn <willemb@...gle.com>
To: "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, bpf@...r.kernel.org, netdev@...r.kernel.org,
martin.lau@...ux.dev, song@...nel.org, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com,
jolsa@...nel.org, sdf@...gle.com
Subject: Re: [PATCH bpf-next 1/2] bpf: Add ipip6 and ip6ip decap support for bpf_skb_adjust_room()
On Mon, Jan 9, 2023 at 4:20 AM Ziyang Xuan (William)
<william.xuanziyang@...wei.com> wrote:
>
> > On Fri, Jan 6, 2023 at 2:55 PM <sdf@...gle.com> wrote:
> >>
> >> On 01/06, Ziyang Xuan wrote:
> >>> Add ipip6 and ip6ip decap support for bpf_skb_adjust_room().
> >>> Main use case is for using cls_bpf on ingress hook to decapsulate
> >>> IPv4 over IPv6 and IPv6 over IPv4 tunnel packets.
> >>
> >> CC'd Willem since he has done bpf_skb_adjust_room changes in the past.
> >> There might be a lot of GRO/GSO context I'm missing.
> >>
> >>> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
> >>> ---
> >>> net/core/filter.c | 34 ++++++++++++++++++++++++++++++++--
> >>> 1 file changed, 32 insertions(+), 2 deletions(-)
> >>
> >>> diff --git a/net/core/filter.c b/net/core/filter.c
> >>> index 929358677183..73982fb4fe2e 100644
> >>> --- a/net/core/filter.c
> >>> +++ b/net/core/filter.c
> >>> @@ -3495,6 +3495,12 @@ static int bpf_skb_net_grow(struct sk_buff *skb,
> >>> u32 off, u32 len_diff,
> >>> static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> >>> u64 flags)
> >>> {
> >>> + union {
> >>> + struct iphdr *v4;
> >>> + struct ipv6hdr *v6;
> >>> + unsigned char *hdr;
> >>> + } ip;
> >>> + __be16 proto;
> >>> int ret;
> >>
> >>> if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO |
> >>> @@ -3512,10 +3518,19 @@ static int bpf_skb_net_shrink(struct sk_buff
> >>> *skb, u32 off, u32 len_diff,
> >>> if (unlikely(ret < 0))
> >>> return ret;
> >>
> >>> + ip.hdr = skb_inner_network_header(skb);
> >>> + if (ip.v4->version == 4)
> >>> + proto = htons(ETH_P_IP);
> >>> + else
> >>> + proto = htons(ETH_P_IPV6);
> >>> +
> >>> ret = bpf_skb_net_hdr_pop(skb, off, len_diff);
> >>> if (unlikely(ret < 0))
> >>> return ret;
> >>
> >>> + /* Match skb->protocol to new outer l3 protocol */
> >>> + skb->protocol = proto;
> >>> +
> >>> if (skb_is_gso(skb)) {
> >>> struct skb_shared_info *shinfo = skb_shinfo(skb);
> >>
> >>> @@ -3578,10 +3593,14 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *,
> >>> skb, s32, len_diff,
> >>> u32, mode, u64, flags)
> >>> {
> >>> u32 len_cur, len_diff_abs = abs(len_diff);
> >>> - u32 len_min = bpf_skb_net_base_len(skb);
> >>> - u32 len_max = BPF_SKB_MAX_LEN;
> >>> + u32 len_min, len_max = BPF_SKB_MAX_LEN;
> >>> __be16 proto = skb->protocol;
> >>> bool shrink = len_diff < 0;
> >>> + union {
> >>> + struct iphdr *v4;
> >>> + struct ipv6hdr *v6;
> >>> + unsigned char *hdr;
> >>> + } ip;
> >>> u32 off;
> >>> int ret;
> >>
> >>> @@ -3594,6 +3613,9 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *,
> >>> skb, s32, len_diff,
> >>> proto != htons(ETH_P_IPV6)))
> >>> return -ENOTSUPP;
> >>
> >>> + if (unlikely(shrink && !skb->encapsulation))
> >>> + return -ENOTSUPP;
> >>> +
> >
> > This new restriction might break existing users.
> >
> > There is no pre-existing requirement that shrink is used solely with
> > packets encapsulated by the protocol stack.
> >
> > Indeed, skb->encapsulation is likely not set on packets arriving from
> > the wire, even if encapsulated. Referring to your comment "Main use
> > case is for using cls_bpf on ingress hook to decapsulate"
> >
> > Can a combination of the existing bpf_skb_adjust_room and
> > bpf_skb_change_proto address your problem?
>
> Hello Willem,
>
> I think combination bpf_skb_adjust_room and bpf_skb_change_proto can not
> address my problem.
>
> Now, bpf_skb_adjust_room() would fail for "len_cur - len_diff_abs < len_min"
> when decap ipip6 packet, because "len_min" should be sizeof(struct iphdr)
> but not sizeof(struct ipv6hdr).
>
> We can remove skb->encapsulation restriction and parse outer and inner IP
> header to determine ipip6 and ip6ip packets. As following:
Adding logic for network layer protocol conversion like this looks
good to me. bpf_skb_adjust_room already has a few other metadata
quirks.
But like those, let's make this intent explicit: define a new flag
that requests this behavior.
Let's avoid introducing a new union. Just use check (ip_hdr(skb)->version == 4).
>
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3498,6 +3498,12 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> u64 flags)
> {
> + union {
> + struct iphdr *v4;
> + struct ipv6hdr *v6;
> + unsigned char *hdr;
> + } ip;
> + __be16 proto;
> int ret;
>
> if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO |
> @@ -3515,10 +3521,23 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> if (unlikely(ret < 0))
> return ret;
>
> + ip.hdr = skb_network_header(skb);
> + if (ip.v4->version == 4) {
> + if (ip.v4->protocol == IPPROTO_IPV6)
> + proto = htons(ETH_P_IPV6);
> + } else {
> + struct ipv6_opt_hdr *opt_hdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) + sizeof(struct ipv6hdr));
> + if (ip.v6->nexthdr == NEXTHDR_DEST && opt_hdr->nexthdr == NEXTHDR_IPV4)
> + proto = htons(ETH_P_IP);
> + }
> +
> ret = bpf_skb_net_hdr_pop(skb, off, len_diff);
> if (unlikely(ret < 0))
> return ret;
>
> + /* Match skb->protocol to new outer l3 protocol */
> + skb->protocol = proto;
> +
> if (skb_is_gso(skb)) {
> struct skb_shared_info *shinfo = skb_shinfo(skb);
>
> @@ -3585,6 +3604,11 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> u32 len_max = BPF_SKB_MAX_LEN;
> __be16 proto = skb->protocol;
> bool shrink = len_diff < 0;
> + union {
> + struct iphdr *v4;
> + struct ipv6hdr *v6;
> + unsigned char *hdr;
> + } ip;
> u32 off;
> int ret;
>
> @@ -3608,6 +3632,19 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> return -ENOTSUPP;
> }
>
> + if (shrink) {
> + ip.hdr = skb_network_header(skb);
> + if (ip.v4->version == 4) {
> + if (ip.v4->protocol == IPPROTO_IPV6)
> + len_min = sizeof(struct ipv6hdr);
> + } else {
> + struct ipv6_opt_hdr *opt_hdr = (struct ipv6_opt_hdr *)(skb_network_header(skb) + sizeof(struct ipv6hdr));
> + if (ip.v6->nexthdr == NEXTHDR_DEST && opt_hdr->nexthdr == NEXTHDR_IPV4) {
> + len_min = sizeof(struct iphdr);
> + }
> + }
> + }
> +
> len_cur = skb->len - skb_network_offset(skb);
>
>
> Look forward to your comments and suggestions.
>
> Thank you!
>
> >
> >>> off = skb_mac_header_len(skb);
> >>> switch (mode) {
> >>> case BPF_ADJ_ROOM_NET:
> >>> @@ -3605,6 +3627,14 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *,
> >>> skb, s32, len_diff,
> >>> return -ENOTSUPP;
> >>> }
> >>
> >>> + if (shrink) {
> >>> + ip.hdr = skb_inner_network_header(skb);
> >>> + if (ip.v4->version == 4)
> >>> + len_min = sizeof(struct iphdr);
> >>> + else
> >>> + len_min = sizeof(struct ipv6hdr);
> >>> + }
> >>> +
> >>> len_cur = skb->len - skb_network_offset(skb);
> >>> if ((shrink && (len_diff_abs >= len_cur ||
> >>> len_cur - len_diff_abs < len_min)) ||
> >>> --
> >>> 2.25.1
> >>
> > .
> >
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