bpf: fix bpf helpers to use skb->mac_header relative offsets

For the short-term solution, lets fix bpf helper functions to use
skb->mac_header relative offsets instead of skb->data in order to
get the same eBPF programs with cls_bpf and act_bpf work on ingress
and egress qdisc path. We need to ensure that mac_header is set
before calling into programs. This is effectively the first option
from below referenced discussion.

More long term solution for LD_ABS|LD_IND instructions will be more
intrusive but also more beneficial than this, and implemented later
as it's too risky at this point in time.

I.e., we plan to look into the option of moving skb_pull() out of
eth_type_trans() and into netif_receive_skb() as has been suggested
as second option. Meanwhile, this solution ensures ingress can be
used with eBPF, too, and that we won't run into ABI troubles later.
For dealing with negative offsets inside eBPF helper functions,
we've implemented bpf_skb_clone_unwritable() to test for unwriteable
headers.

Reference: http://thread.gmane.org/gmane.linux.network/359129/focus=359694
Fixes: 608cd71a9c7c ("tc: bpf: generalize pedit action")
Fixes: 91bc4822c3d6 ("tc: bpf: add checksum helpers")
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 34c7936ca114..c97340e43dd6 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -79,8 +79,11 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_RANDOM	56
 #define SKF_AD_VLAN_TPID	60
 #define SKF_AD_MAX	64
-#define SKF_NET_OFF   (-0x100000)
-#define SKF_LL_OFF    (-0x200000)
 
+#define SKF_NET_OFF	(-0x100000)
+#define SKF_LL_OFF	(-0x200000)
+
+#define BPF_NET_OFF	SKF_NET_OFF
+#define BPF_LL_OFF	SKF_LL_OFF
 
 #endif /* _UAPI__LINUX_FILTER_H__ */