Re: [PATCH bpf-next v3 01/10] bpf: Add dynptr type for skb metadata

On Tue, Jul 22, 2025 at 05:37 PM -07, Martin KaFai Lau wrote:

On 7/21/25 3:52 AM, Jakub Sitnicki wrote:

quoted

@@ -21788,12 +21798,17 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
  	if (offset)
  		return;
  -	if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
+	if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb] ||
+	    func_id == special_kfunc_list[KF_bpf_dynptr_from_skb_meta]) {

I don't think this check is needed. The skb_meta is writable to tc.

quoted

  		seen_direct_write = env->seen_direct_write;
  		is_rdonly = !may_access_direct_pkt_data(env, NULL, BPF_WRITE);

is_rdonly is always false here.

quoted

  -		if (is_rdonly)
-			*addr = (unsigned long)bpf_dynptr_from_skb_rdonly;
+		if (is_rdonly) {
+			if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb])
+				*addr = (unsigned long)bpf_dynptr_from_skb_rdonly;
+			else if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb_meta])
+				*addr = (unsigned long)bpf_dynptr_from_skb_meta_rdonly;
+		}

[ ... ]

quoted

+int bpf_dynptr_from_skb_meta_rdonly(struct __sk_buff *skb, u64 flags,

so I suspect this is never used and not needed now. Please check.
It can be revisited in the future when other hooks are supported. It will be a
useful comment in the commit message.

You're right. This is dead code ATM. I missed that. Will remove.

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