Re: [bpf-next PATCH v2 05/18] bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data

Daniel Borkmann
2018-03-15T22:17:17Z

On 03/15/2018 10:59 PM, Alexei Starovoitov wrote:
> On Mon, Mar 12, 2018 at 12:23:29PM -0700, John Fastabend wrote:
>>
>> +/* User return codes for SK_MSG prog type. */
>> +enum sk_msg_action {
>> + SK_MSG_DROP = 0,
>> + SK_MSG_PASS,
>> +};
>
> do we really need new enum here?
> It's the same as 'enum sk_action' and SK_DROP == SK_MSG_DROP
> and there will be only drop/pass in both enums.
> Also I don't see where these two new SK_MSG_* are used...
>
>> +
>> +/* user accessible metadata for SK_MSG packet hook, new fields must
>> + * be added to the end of this structure
>> + */
>> +struct sk_msg_md {
>> + __u32 data;
>> + __u32 data_end;
>> +};
>
> I think it's time for me to ask for forgiveness :)

:-)

> I used __u32 for data and data_end only because all other fields
> in __sk_buff were __u32 at the time and I couldn't easily figure out
> how to teach verifier to recognize 8-byte rewrites.
> Unfortunately my mistake stuck and was copied over into xdp.
> Since this is new struct let's do it right and add
> 'void *data, *data_end' here,
> since bpf prog will use them as 'void *' pointers.
> There are no compat issues here, since bpf is always 64-bit.

But at least offset-wise when you do the ctx rewrite this would then
be a bit more tricky when you have 64 bit kernel with 32 bit user
space since void * members are in each cases at different offset. So
unless I'm missing something, this still should either be __u32 or
__u64 instead of void *, no?

>> +static int bpf_map_msg_verdict(int _rc, struct sk_msg_buff *md)
>> +{
>> + return ((_rc == SK_PASS) ?
>> + (md->map ? __SK_REDIRECT : __SK_PASS) :
>> + __SK_DROP);
>
> you're using old SK_PASS here too ;)
> that's to my point of not adding SK_MSG_PASS...
>
> Overall the patch set looks absolutely great.
> Thank you for working on it.

+1