Re: [PATCH v9 06/10] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

[Daniel Borkmann <daniel@iogearbox.net>]

[...]
>>> +noinline __weak struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
>>
>> Why the need for noinline and the __weak here and below? (If indeed needed
>> this
>> should probably be explained in the commit desc.)
> 
> Oh, I took from v3 of KP's patch set. It is gone in v5. Will do
> the same as well.
> 
>>> +{
>>> +	key_ref_t key_ref;
>>> +	struct bpf_key *bkey;
>>> +
>>> +	/* Keep in sync with include/linux/key.h. */
>>> +	if (flags > (KEY_LOOKUP_PARTIAL << 1) - 1)
>>
>> Can't we just simplify and test flags &
>> ~(KEY_LOOKUP_CREATE|KEY_LOOKUP_PARTIAL)?
> 
> I thought as if we have many flags.

I'd keep it simple for now, and if the actual need comes this can still be changed.

>>> +		return NULL;
>>> +
>>> +	/* Permission check is deferred until actual kfunc using the key. */
>>> +	key_ref = lookup_user_key(serial, flags, KEY_DEFER_PERM_CHECK);
>>> +	if (IS_ERR(key_ref))
>>> +		return NULL;
>>> +
>>> +	bkey = kmalloc(sizeof(*bkey), GFP_KERNEL);
>>> +	if (!bkey) {
>>> +		key_put(key_ref_to_ptr(key_ref));
>>> +		return bkey;
>>
>> nit: just return NULL probably cleaner
> 
> Ok.