[PATCH bpf-next 1/2] bpf: Add ipip6 and ip6ip decap support for bpf_skb_adjust_room()

[Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>]

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.

Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
---
 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;
+
 	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