Re: [PATCH v2 3/5] bpf: add helper masks for ADJ_ROOM flags and encap validation

On 3/26/26 10:02 AM, Hudson, Nick wrote:

quoted

quoted

    static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
       u64 flags)

@@ -3502,6 +3513,11 @@ 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)))

Under which case this new check will be hit?

If a user supplies +ve len_diff and attempts to pass a DECAP flag.

The commit message had

     Add flag validation to bpf_skb_net_grow() to reject invalid encap
     flags early.

There is DECAP_MASK check in bpf_skb_adjust_room() and then !shrink is 
rejected. What am I missing?