tree 295b1d647364407c42990d916358a72381f4d534
parent 3431205e03977aaf32bce6d4b16fb8244b510056
author Alexei Starovoitov <ast@plumgrid.com> 1433437914 -0700
committer David S. Miller <davem@davemloft.net> 1433667693 -0700

bpf: allow programs to write to certain skb fields

allow programs read/write skb->mark, tc_index fields and
((struct qdisc_skb_cb *)cb)->data.

mark and tc_index are generically useful in TC.
cb[0]-cb[4] are primarily used to pass arguments from one
program to another called via bpf_tail_call() which can
be seen in sockex3_kern.c example.

All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs.
mark, tc_index are writeable from tc_cls_act only.
cb[0]-cb[4] are writeable by both sockets and tc_cls_act.

Add verifier tests and improve sample code.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>