On 10/26/23 1:13 AM, Jamal Hadi Salim wrote:
On Wed, Oct 25, 2023 at 9:46 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 10/25/23 3:21 PM, Jamal Hadi Salim wrote:
On Wed, Oct 25, 2023 at 7:52 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 10/25/23 1:05 PM, Jamal Hadi Salim wrote:
On Wed, Oct 25, 2023 at 6:01 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 10/25/23 10:59 AM, Ido Schimmel wrote:
On Mon, Oct 09, 2023 at 11:26:54AM +0200, Daniel Borkmann wrote:
diff --git a/net/core/dev.c b/net/core/dev.c
index 606a366cc209..664426285fa3 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3910,7 +3910,8 @@ EXPORT_SYMBOL_GPL(netdev_xmit_skip_txqueue);
#endif /* CONFIG_NET_EGRESS */
#ifdef CONFIG_NET_XGRESS
-static int tc_run(struct tcx_entry *entry, struct sk_buff *skb)
+static int tc_run(struct tcx_entry *entry, struct sk_buff *skb,
+ enum skb_drop_reason *drop_reason)
{
int ret = TC_ACT_UNSPEC;
#ifdef CONFIG_NET_CLS_ACT
@@ -3922,12 +3923,14 @@ static int tc_run(struct tcx_entry *entry, struct sk_buff *skb)
tc_skb_cb(skb)->mru = 0;
tc_skb_cb(skb)->post_ct = false;
+ res.drop_reason = *drop_reason;
mini_qdisc_bstats_cpu_update(miniq, skb);
ret = tcf_classify(skb, miniq->block, miniq->filter_list, &res, false);
/* Only tcf related quirks below. */
switch (ret) {
case TC_ACT_SHOT:
+ *drop_reason = res.drop_reason;
Daniel,
Getting the following splat [1] with CONFIG_DEBUG_NET=y and this
reproducer [2]. Problem seems to be that classifiers clear 'struct
tcf_result::drop_reason', thereby triggering the warning in
__kfree_skb_reason() due to reason being 'SKB_NOT_DROPPED_YET' (0).
Fixed by maintaining the original drop reason if the one returned from
tcf_classify() is 'SKB_NOT_DROPPED_YET' [3]. I can submit this fix
unless you have a better idea.
Thanks for catching this, looks reasonable to me as a fix.
[1]
WARNING: CPU: 0 PID: 181 at net/core/skbuff.c:1082 kfree_skb_reason+0x38/0x130
Modules linked in:
CPU: 0 PID: 181 Comm: mausezahn Not tainted 6.6.0-rc6-custom-ge43e6d9582e0 #682
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc37 04/01/2014
RIP: 0010:kfree_skb_reason+0x38/0x130
[...]
Call Trace:
<IRQ>
__netif_receive_skb_core.constprop.0+0x837/0xdb0
__netif_receive_skb_one_core+0x3c/0x70
process_backlog+0x95/0x130
__napi_poll+0x25/0x1b0
net_rx_action+0x29b/0x310
__do_softirq+0xc0/0x29b
do_softirq+0x43/0x60
</IRQ>
[2]
#!/bin/bash
ip link add name veth0 type veth peer name veth1
ip link set dev veth0 up
ip link set dev veth1 up
tc qdisc add dev veth1 clsact
tc filter add dev veth1 ingress pref 1 proto all flower dst_mac 00:11:22:33:44:55 action drop
mausezahn veth0 -a own -b 00:11:22:33:44:55 -q -c 1
I didn't know you're using mausezahn, nice :)
[3]
diff --git a/net/core/dev.c b/net/core/dev.c
index a37a932a3e14..abd0b13f3f17 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3929,7 +3929,8 @@ static int tc_run(struct tcx_entry *entry, struct sk_buff *skb,
/* Only tcf related quirks below. */
switch (ret) {
case TC_ACT_SHOT:
- *drop_reason = res.drop_reason;
+ if (res.drop_reason != SKB_NOT_DROPPED_YET)
+ *drop_reason = res.drop_reason;
mini_qdisc_qstats_cpu_drop(miniq);
break;
case TC_ACT_OK:
Out of curiosity - how does the policy say "drop" but drop_reason does
not reflect it?
Ido, Jamal, wdyt about this alternative approach - these were the locations I could
find from an initial glance (compile-tested) :
From a3d46a55aac484372b60b783cb6a3c98a0fef75c Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Date: Wed, 25 Oct 2023 11:43:44 +0000
Subject: [PATCH] net, sched: fix..
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
include/net/pkt_cls.h | 12 ++++++++++++
net/sched/cls_basic.c | 2 +-
net/sched/cls_bpf.c | 2 +-
net/sched/cls_flower.c | 2 +-
net/sched/cls_fw.c | 2 +-
net/sched/cls_matchall.c | 2 +-
net/sched/cls_route.c | 4 ++--
net/sched/cls_u32.c | 2 +-
8 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index a76c9171db0e..31d8e8587824 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -160,6 +160,18 @@ static inline void tcf_set_drop_reason(struct tcf_result *res,
res->drop_reason = reason;
}
+static inline void tcf_set_result(struct tcf_result *to,
+ const struct tcf_result *from)
+{
+ /* tcf_result's drop_reason which is the last member must be
+ * preserved and cannot be copied from the cls'es tcf_result
+ * template given this is carried all the way and potentially
+ * set to a concrete tc drop reason upon error or intentional
+ * drop. See tcf_set_drop_reason() locations.
+ */
+ memcpy(to, from, offsetof(typeof(*to), drop_reason));
+}
+
Daniel, IMO, doing this at cls_api is best instead (like what Victors
or my original patch did). Iam ~30K feet right now with a lousy
keyboard - you can either do it, or i or Victor can send the patch by
end of day today. There are missing cases which were covered by Victor
and possibly something else will pop up next.
Sure, if you have sth clean and simple for today, go for it. Otherwise I
can cook a proper one out of this as a fix and ship it tomorrow AM, so we
have a fix for the splat in CONFIG_DEBUG_NET kernels and you can still
refactor later.
I was thinking something along these lines:
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1662,6 +1662,7 @@ static inline int __tcf_classify(struct sk_buff *skb,
const int max_reclassify_loop = 16;
const struct tcf_proto *first_tp;
int limit = 0;
+ u32 reason_code = res->drop_reason;
reclassify:
#endif
@@ -1712,8 +1713,11 @@ static inline int __tcf_classify(struct sk_buff *skb,
goto reset;
}
#endif
- if (err >= 0)
+ if (err >= 0) {
+ if (err == TC_ACT_SHOT) /* policy drop */
+ tcf_set_drop_reason(res, orig_reason);
return err;
+ }
}
if (unlikely(n)) {
But tbh, i am struggling with the whole approach you took in the
earlier patch - i.e setting the drop reason from cls_act and then
expecting it not to be changed on policy drops; while it works for
clsact, it is not going to work for the rest of the qdiscs - unless we
change all the qdisc enqueues to take an extra param for drop_reason.
Thoughts?
The downside of the above would be that you then cannot make use of
tcf_set_drop_reason() further down the tc engine, for example, within
classifiers/actions, e.g. tcf_action_exec() where you also have drops
like:
[...]
} else if (TC_ACT_EXT_CMP(ret, TC_ACT_GOTO_CHAIN)) {
if (unlikely(!rcu_access_pointer(a->goto_chain))) {
net_warn_ratelimited("can't go to NULL chain!\n");
return TC_ACT_SHOT;
}
tcf_action_goto_chain_exec(a, res);
}
[...]
If I spot this correctly, qdiscs also use tcf_classify() as well, and
so far none of them have kfree_skb_reason() support, but if you plan to
add it you can just set a default res.drop_reason from there as well
since tcf_classify() already takes the res param.
Thanks,
Daniel
