On 01/12/2019 03:55 AM, Cong Wang wrote:
> Martin reported a set of filters don't work after changing
> from reclassify to continue. Looking into the code, it
> looks like skb protocol is not always fetched for each
> iteration of the filters. But, as demonstrated by Martin,
> TC actions could modify skb->protocol, for example act_vlan,
> this means we have to refetch skb protocol in each iteration,
> rather than using the one we fetch in the beginning of the loop.
>
> This bug is _not_ introduced by commit 3b3ae880266d
> ("net: sched: consolidate tc_classify{,_compat}"), technically,
> if act_vlan is the only action that modifies skb protocol, then
> it is commit c7e2b9689ef8 ("sched: introduce vlan action") which
> introduced this bug.
>
> Reported-by: Martin Olsson <[email protected]>
> Cc: Jamal Hadi Salim <[email protected]>
> Cc: Jiri Pirko <[email protected]>
> Signed-off-by: Cong Wang <[email protected]>
> ---
> net/sched/cls_api.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 8ce2a0507970..e2b5cb2eb34e 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -1277,7 +1277,6 @@ EXPORT_SYMBOL(tcf_block_cb_unregister);
> int tcf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
> struct tcf_result *res, bool compat_mode)
> {
> - __be16 protocol = tc_skb_protocol(skb);
> #ifdef CONFIG_NET_CLS_ACT
> const int max_reclassify_loop = 4;
> const struct tcf_proto *orig_tp = tp;
> @@ -1287,6 +1286,7 @@ int tcf_classify(struct sk_buff *skb, const struct
> tcf_proto *tp,
> reclassify:
> #endif
> for (; tp; tp = rcu_dereference_bh(tp->next)) {
> + __be16 protocol = tc_skb_protocol(skb);
> int err;
>
> if (tp->protocol != protocol &&
Can't we do something like the below instead? Otherwise we'll needlessly refetch
protocol every time there is a mismatch in above tp->protocol check as well.
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 8ce2a05..dc725a1 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1305,6 +1305,11 @@ int tcf_classify(struct sk_buff *skb, const struct
tcf_proto *tp,
#endif
if (err >= 0)
return err;
+
+ /* We also need to refetch protocol from here as e.g.
+ * act_vlan could have changed it.
+ */
+ protocol = tc_skb_protocol(skb);
}
return TC_ACT_UNSPEC; /* signal: continue lookup */
Thanks,
Daniel
