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@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 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 @@
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):