Re: [PATCH bpf-next] bpf: Check cfi_stubs before registering a struct_ops type.

[Martin KaFai Lau <martin.lau@linux.dev>]

On 2/14/24 6:24 PM, thinker.li@gmail.com wrote:
> From: Kui-Feng Lee <thinker.li@gmail.com>
> 
> Recently, cfi_stubs were introduced. However, existing struct_ops types
> that are not in the upstream may not be aware of this, resulting in kernel
> crashes. By rejecting struct_ops types that do not provide cfi_stubs during
> registration, these crashes can be avoided.
> 
> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
> ---
>   kernel/bpf/bpf_struct_ops.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 0d7be97a2411..e35958142dce 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -302,6 +302,11 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
>   	}
>   	sprintf(value_name, "%s%s", VALUE_PREFIX, st_ops->name);
>   
> +	if (!st_ops->cfi_stubs) {

How about *(void **)(st_ops->cfi_stubs + moff) ? Does it need a NULL check?

Please add a test.

> +		pr_warn("The struct_ops %s has no cfi_stubs\n", st_ops->name);
> +		return -EINVAL;
> +	}
> +
>   	type_id = btf_find_by_name_kind(btf, st_ops->name,
>   					BTF_KIND_STRUCT);
>   	if (type_id < 0) {