Subject: Re: [PATCH net-next] act_bpf: properly support late binding of bpf action to a classifier

From: Alexei Starovoitov <[email-masked]>
Date: Mon, 3 Aug 2015 09:36:04 -0700

On 8/3/15 7:21 AM, Daniel Borkmann wrote:
> Since the introduction of the BPF action in d23b8ad8ab23 ("tc: add BPF
> based action"), late binding was not working as expected. I.e. setting
> the action part for a classifier only via 'bpf index <num>', where <num>
> is the index of an existing action, is being rejected by the kernel due
> to other missing parameters.
>
> It doesn't make sense to require these parameters such as BPF opcodes
> etc, as they are not going to be used anyway: in this case, they're just
> allocated/parsed and then freed again w/o doing anything meaningful.
>
> Instead, parse and verify the remaining parameters*after*  the test on
> tcf_hash_check(), when we really know that we're dealing with creation
> of a new action or replacement of an existing one and where late binding
> is thus irrelevant.
>
> After patch, test case is now working:
>
>    FOO="1,6 0 0 4294967295,"
>    tc actions add action bpf bytecode "$FOO"
>    tc filter add dev foo parent 1: bpf bytecode "$FOO" flowid 1:1 action bpf index 1
>    tc actions show action bpf
>      action order 0: bpf bytecode '1,6 0 0 4294967295' default-action pipe
>      index 1 ref 2 bind 1
>    tc filter show dev foo
>      filter protocol all pref 49152 bpf
>      filter protocol all pref 49152 bpf handle 0x1 flowid 1:1 bytecode '1,6 0 0 4294967295'
>      action order 1: bpf bytecode '1,6 0 0 4294967295' default-action pipe
>      index 1 ref 2 bind 1
>
> Late binding of a BPF action can be useful for preloading maps (e.g. before
> they hit traffic) in case of eBPF programs, or to share a single eBPF action
> with multiple classifiers.
>
> Signed-off-by: Daniel Borkmann<[email-masked]>
> ---
>   This one was still in my queue of fixes, net-next is totally fine here.
>   Will push out minor iproute2 change afterwards.

All makes sense.
Acked-by: Alexei Starovoitov <[email-masked]>