bpf: Set kptr_struct_meta for node param to list and rbtree insert funcs

In verifier.c, fixup_kfunc_call uses struct bpf_insn_aux_data's
kptr_struct_meta field to pass information about local kptr types to
various helpers and kfuncs at runtime. The recent bpf_refcount series
added a few functions to the set that need this information:

  * bpf_refcount_acquire
    * Needs to know where the refcount field is in order to increment
  * Graph collection insert kfuncs: bpf_rbtree_add, bpf_list_push_{front,back}
    * Were migrated to possibly fail by the bpf_refcount series. If
      insert fails, the input node is bpf_obj_drop'd. bpf_obj_drop needs
      the kptr_struct_meta in order to decr refcount and properly free
      special fields.

Unfortunately the verifier handling of collection insert kfuncs was not
modified to actually populate kptr_struct_meta. Accordingly, when the
node input to those kfuncs is passed to bpf_obj_drop, it is done so
without the information necessary to decr refcount.

This patch fixes the issue by populating kptr_struct_meta for those
kfuncs.

Fixes: d2dcc67 ("bpf: Migrate bpf_rbtree_add and bpf_list_push_{front,back} to possibly fail")
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>

kernel/bpf/verifier.c

@@ -10475,6 +10475,8 @@ __process_kf_arg_ptr_to_graph_node(struct bpf_verifier_env *env,
 			node_off, btf_name_by_offset(reg->btf, t->name_off));
 		return -EINVAL;
 	}
+	meta->arg_btf = reg->btf;
+	meta->arg_btf_id = reg->btf_id;
 
 	if (node_off != field->graph_root.node_offset) {
 		verbose(env, "arg#1 offset=%d, but expected %s at offset=%d in struct %s\n",
@@ -11040,6 +11042,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	    meta.func_id == special_kfunc_list[KF_bpf_rbtree_add_impl]) {
 		release_ref_obj_id = regs[BPF_REG_2].ref_obj_id;
 		insn_aux->insert_off = regs[BPF_REG_2].off;
+		insn_aux->kptr_struct_meta = btf_find_struct_meta(meta.arg_btf, meta.arg_btf_id);
 		err = ref_convert_owning_non_owning(env, release_ref_obj_id);
 		if (err) {
 			verbose(env, "kfunc %s#%d conversion of owning ref to non-owning failed\n",