[PATCH v1 3/5] bpf: add helper masks for ADJ_ROOM decap flags

[Nick Hudson]

Introduce helper masks for bpf_skb_adjust_room() decapsulation flags
to simplify validation and keep flag handling readable:

- BPF_F_ADJ_ROOM_DECAP_L4_MASK
- BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK
- BPF_F_ADJ_ROOM_ENCAP_MASK
- BPF_F_ADJ_ROOM_DECAP_MASK

Also fold these masks into BPF_F_ADJ_ROOM_MASK and per-path flag
validation checks.

This is a refactoring/plumbing change; functional decapsulation and
GSO behavior updates are handled in later patches.

Co-developed-by: Max Tottenham <mtottenh@xxxxxxxxxx>
Signed-off-by: Max Tottenham <mtottenh@xxxxxxxxxx>
Co-developed-by: Anna Glasgall <aglasgal@xxxxxxxxxx>
Signed-off-by: Anna Glasgall <aglasgal@xxxxxxxxxx>
Signed-off-by: Nick Hudson <nhudson@xxxxxxxxxx>
---
 net/core/filter.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 0d5d5a17acb2..ac7e1068fe4c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3483,14 +3483,27 @@ 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_MASK		(BPF_F_ADJ_ROOM_FIXED_GSO | \
-					 BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \
+#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 | \
 					 BPF_F_ADJ_ROOM_ENCAP_L2_ETH | \
 					 BPF_F_ADJ_ROOM_ENCAP_L2( \
-					  BPF_ADJ_ROOM_ENCAP_L2_MASK) | \
-					 BPF_F_ADJ_ROOM_DECAP_L3_MASK)
+					  BPF_ADJ_ROOM_ENCAP_L2_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 | \
+					 BPF_F_ADJ_ROOM_DECAP_MASK | \
+					 BPF_F_ADJ_ROOM_NO_CSUM_RESET)
 
 static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 			    u64 flags)
@@ -3502,6 +3515,11 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
 	unsigned int gso_type = SKB_GSO_DODGY;
 	int ret;
 
+	if (unlikely(flags & ~(BPF_F_ADJ_ROOM_ENCAP_MASK |
+			       BPF_F_ADJ_ROOM_NO_CSUM_RESET |
+			       BPF_F_ADJ_ROOM_FIXED_GSO)))
+		return -EINVAL;
+
 	if (skb_is_gso(skb) && !skb_is_gso_tcp(skb)) {
 		/* udp gso_size delineates datagrams, only allow if fixed */
 		if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) ||
@@ -3611,8 +3629,8 @@ 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 |
+	if (unlikely(flags & ~(BPF_F_ADJ_ROOM_DECAP_MASK |
+			       BPF_F_ADJ_ROOM_FIXED_GSO |
 			       BPF_F_ADJ_ROOM_NO_CSUM_RESET)))
 		return -EINVAL;
 
@@ -3708,8 +3726,7 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
 	u32 off;
 	int ret;
 
-	if (unlikely(flags & ~(BPF_F_ADJ_ROOM_MASK |
-			       BPF_F_ADJ_ROOM_NO_CSUM_RESET)))
+	if (unlikely(flags & ~BPF_F_ADJ_ROOM_MASK))
 		return -EINVAL;
 	if (unlikely(len_diff_abs > 0xfffU))
 		return -EFAULT;
-- 
2.34.1