[PATCH net-next v2 2/2] net, sched: Add tcf_set_drop_reason for {__,}tcf_classify

Daniel Borkmann
2023-10-09T09:27:08Z

Add an initial user for the newly added tcf_set_drop_reason() helper to set the
drop reason for internal errors leading to TC_ACT_SHOT inside {__,}tcf_classify().

Right now this only adds a very basic SKB_DROP_REASON_TC_ERROR as a generic
fallback indicator to mark drop locations. Where needed, such locations can be
converted to more specific codes, for example, when hitting the reclassification
limit, etc.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Victor Nogueira <victor@mojatatu.com>
Cc: Jakub Kicinski <kuba@kernel.org>
---
include/net/dropreason-core.h | 3 +++
net/sched/cls_api.c | 26 ++++++++++++++++++++------
2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index a587e83fc169..845dce805de7 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -80,6 +80,7 @@
FN(IPV6_NDISC_BAD_OPTIONS) \
FN(IPV6_NDISC_NS_OTHERHOST) \
FN(QUEUE_PURGE) \
+ FN(TC_ERROR) \
FNe(MAX)

/**
@@ -345,6 +346,8 @@ enum skb_drop_reason {
SKB_DROP_REASON_IPV6_NDISC_NS_OTHERHOST,
/** @SKB_DROP_REASON_QUEUE_PURGE: bulk free. */
SKB_DROP_REASON_QUEUE_PURGE,
+ /** @SKB_DROP_REASON_TC_ERROR: generic internal tc error. */
+ SKB_DROP_REASON_TC_ERROR,
/**
* @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
* shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index a193cc7b3241..1daeb2182b70 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1681,12 +1681,16 @@ static inline int __tcf_classify(struct sk_buff *skb,
* time we got here with a cookie from hardware.
*/
if (unlikely(n->tp != tp || n->tp->chain != n->chain ||
- !tp->ops->get_exts))
+ !tp->ops->get_exts)) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }

exts = tp->ops->get_exts(tp, n->handle);
- if (unlikely(!exts || n->exts != exts))
+ if (unlikely(!exts || n->exts != exts)) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }

n = NULL;
err = tcf_exts_exec_ex(skb, exts, act_index, res);
@@ -1712,8 +1716,10 @@ static inline int __tcf_classify(struct sk_buff *skb,
return err;
}

- if (unlikely(n))
+ if (unlikely(n)) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }

return TC_ACT_UNSPEC; /* signal: continue lookup */
#ifdef CONFIG_NET_CLS_ACT
@@ -1723,6 +1729,7 @@ static inline int __tcf_classify(struct sk_buff *skb,
tp->chain->block->index,
tp->prio & 0xffff,
ntohs(tp->protocol));
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
}

@@ -1759,8 +1766,10 @@ int tcf_classify(struct sk_buff *skb,
if (ext->act_miss) {
n = tcf_exts_miss_cookie_lookup(ext->act_miss_cookie,
&act_index);
- if (!n)
+ if (!n) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }

chain = n->chain_index;
} else {
@@ -1768,8 +1777,10 @@ int tcf_classify(struct sk_buff *skb,
}

fchain = tcf_chain_lookup_rcu(block, chain);
- if (!fchain)
+ if (!fchain) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }

/* Consume, so cloned/redirect skbs won't inherit ext */
skb_ext_del(skb, TC_SKB_EXT);
@@ -1788,8 +1799,11 @@ int tcf_classify(struct sk_buff *skb,
struct tc_skb_cb *cb = tc_skb_cb(skb);

ext = tc_skb_ext_alloc(skb);
- if (WARN_ON_ONCE(!ext))
+ if (WARN_ON_ONCE(!ext)) {
+ tcf_set_drop_reason(res, SKB_DROP_REASON_TC_ERROR);
return TC_ACT_SHOT;
+ }
+
ext->chain = last_executed_chain;
ext->mru = cb->mru;
ext->post_ct = cb->post_ct;
--
2.34.1