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

[Kui-Feng Lee <sinquersw@gmail.com>]

On 2/15/24 10:23, Martin KaFai Lau wrote:
> 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?

This NULL check is necessary to prevent the crash but good to have.

> 
> Please add a test.

Got it!

> 
>> +        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) {
>