On Wed, Oct 17, 2018 at 04:36:15PM -0700, Song Liu wrote: > BPF programs of BPF_PROG_TYPE_CGROUP_SKB need to access headers in the > skb. This patch enables direct access of skb for these programs. > > In __cgroup_bpf_run_filter_skb(), bpf_compute_data_pointers() is called > to compute proper data_end for the BPF program. > > Signed-off-by: Song Liu <songliubrav...@fb.com> > --- > kernel/bpf/cgroup.c | 4 ++++ > net/core/filter.c | 36 +++++++++++++++++++++++++++++++++++- > 2 files changed, 39 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > index 00f6ed2e4f9a..340d496f35bd 100644 > --- a/kernel/bpf/cgroup.c > +++ b/kernel/bpf/cgroup.c > @@ -566,6 +566,10 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk, > save_sk = skb->sk; > skb->sk = sk; > __skb_push(skb, offset); > + > + /* compute pointers for the bpf prog */ > + bpf_compute_data_pointers(skb);
cg_skb_is_valid_access() below looks good to me now, but I just realized that above change is not safe for all sockets. After sk_filter_trim_cap() is called in udp_queue_rcv_skb() it needs to see valid UDP_SKB_CB. But sizeof(struct udp_skb_cb)==28, so bpf_compute_data_pointers() would mangle the end of it. So we have to save/restore data_end/data_meta pointers as well. I'm thinking that new helper like: bpf_compute_and_save_data_pointers(skb, &buffer_of_16_bytes); BPF_PROG_RUN_ARRAY(); bpf_restore_data_pointers(skb, &buffer_of_16_bytes); would be decent interface.
