bpf: net_sched: Use the correct destructor kfunc type

With CONFIG_CFI_CLANG enabled, the kernel strictly enforces that
indirect function calls use a function pointer type that matches
the target function. As bpf_kfree_skb() signature differs from the
btf_dtor_kfunc_t pointer type used for the destructor calls in
bpf_obj_free_fields(), add a stub function with the correct type to
fix the type mismatch.

Signed-off-by: Sami Tolvanen <[email protected]>

Author: samitolvanen

net/sched/bpf_qdisc.c

@@ -202,6 +202,13 @@ __bpf_kfunc void bpf_kfree_skb(struct sk_buff *skb)
 	kfree_skb(skb);
 }
 
+__used __retain void __bpf_kfree_skb(void *skb)
+{
+	bpf_kfree_skb(skb);
+}
+
+CFI_NOSEAL(__bpf_kfree_skb);
+
 /* bpf_qdisc_skb_drop - Drop an skb by adding it to a deferred free list.
  * @skb: The skb whose reference to be released and dropped.
  * @to_free_list: The list of skbs to be dropped.
@@ -449,7 +456,7 @@ static struct bpf_struct_ops bpf_Qdisc_ops = {
 	.owner = THIS_MODULE,
 };
 
-BTF_ID_LIST_SINGLE(bpf_sk_buff_dtor_ids, func, bpf_kfree_skb)
+BTF_ID_LIST_SINGLE(bpf_sk_buff_dtor_ids, func, __bpf_kfree_skb)
 
 static int __init bpf_qdisc_kfunc_init(void)
 {