netdev - [PATCH net-next 1/3] bpf: make skb->tc

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Date:	Wed, 16 Mar 2016 01:42:49 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	davem@...emloft.net
Cc:	alexei.starovoitov@...il.com, netdev@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH net-next 1/3] bpf: make skb->tc_classid also readable

Currently, the tc_classid from eBPF skb context is write-only, but there's
no good reason for tc programs to limit it to write-only. For example,
it can be used to transfer its state via tail calls where the resulting
tc_classid gets filled gradually.

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
 net/core/filter.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 6fc3893..69c7b2f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2069,16 +2069,14 @@ static bool sk_filter_is_valid_access(int off, int size,
 static bool tc_cls_act_is_valid_access(int off, int size,
 				       enum bpf_access_type type)
 {
-	if (off == offsetof(struct __sk_buff, tc_classid))
-		return type == BPF_WRITE ? true : false;
-
 	if (type == BPF_WRITE) {
 		switch (off) {
 		case offsetof(struct __sk_buff, mark):
 		case offsetof(struct __sk_buff, tc_index):
 		case offsetof(struct __sk_buff, priority):
 		case offsetof(struct __sk_buff, cb[0]) ...
-			offsetof(struct __sk_buff, cb[4]):
+		     offsetof(struct __sk_buff, cb[4]):
+		case offsetof(struct __sk_buff, tc_classid):
 			break;
 		default:
 			return false;
@@ -2195,8 +2193,10 @@ static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
 		ctx_off -= offsetof(struct __sk_buff, tc_classid);
 		ctx_off += offsetof(struct sk_buff, cb);
 		ctx_off += offsetof(struct qdisc_skb_cb, tc_classid);
-		WARN_ON(type != BPF_WRITE);
-		*insn++ = BPF_STX_MEM(BPF_H, dst_reg, src_reg, ctx_off);
+		if (type == BPF_WRITE)
+			*insn++ = BPF_STX_MEM(BPF_H, dst_reg, src_reg, ctx_off);
+		else
+			*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg, ctx_off);
 		break;
 
 	case offsetof(struct __sk_buff, tc_index):
-- 
1.9.3