Subject: Re: [PATCH net] net: flow_offload: protect driver_block_list in flow_block_cb_setup_simple()

From: Pablo Neira Ayuso <[email-masked]>
Date: Tue, 17 Feb 2026 12:42:13 +0100

On Sun, Feb 15, 2026 at 02:06:42PM +0100, Florian Westphal wrote:
> Jakub Kicinski <[email-masked]> wrote:
> > On Fri, 13 Feb 2026 12:30:58 +0100 Florian Westphal wrote:
> > > > > Looking at the *upper layer*, I don't think it expected drivers to use
> > > > > a single global list for this bit something that is scoped to the
> > > > > net_device.  
> > > > 
> > > > Maybe subjective but the fix seems a little off to me.
> > > > Isn't flow_block_cb_setup_simple() just a "simple" implementation 
> > > > for reuse in drivers locking in there doesn't really guarantee much?  
> > > 
> > > Not sure what you mean.  I see the same pattern as netdevsim in all
> > > drivers using this API. 
> > 
> > Grep for flow_block_cb_add(). Not all drivers use
> 
> static int
> mtk_eth_setup_tc_block(struct net_device *dev, struct flow_block_offload *f)
> {
>         struct mtk_mac *mac = netdev_priv(dev);
>         struct mtk_eth *eth = mac->hw;
>         static LIST_HEAD(block_cb_list);
> 	~~~~~~
> I have a question.
> 
> [..]
>         f->driver_block_list = &block_cb_list;
> 
> Now I have many questions!
> 
> How is this supposed to work?

Last time I met people, I asked how is hw offload actually working
with netns (6 years ago?), someone told me: "maybe there is a driver
that supports it...". I have never seen one, but I am very much
outdates on how this has evolved TBH, I might be wrong.

I don't think any driver really supports netns + hardware offload, so
I suggest to restrict it, see attached patch.

It would be better to add a helper function such as int net_setup_tc()
for the myriad of ->ndo_setup_tc() calls in the code, then move this
check in it to consolidate, but I think you want something you can
pass to -stable at this stage?
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 99ac747b7906..a97838c1c56d 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -692,6 +692,9 @@ struct tc_cls_u32_offload {
 
 static inline bool tc_can_offload(const struct net_device *dev)
 {
+	if (!net_eq(dev_net(dev), &init_net))
+		return false;
+
 	return dev->features & NETIF_F_HW_TC;
 }
 
diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index b1966b68c48a..c6d426052765 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -1173,6 +1173,9 @@ static int nf_flow_table_offload_cmd(struct flow_block_offload *bo,
 {
 	int err;
 
+	if (!net_eq(dev_net(dev), &init_net))
+		return -EOPNOTSUPP;
+
 	nf_flow_table_block_offload_init(bo, dev_net(dev), cmd, flowtable,
 					 extack);
 	down_write(&flowtable->flow_block_lock);
diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
index fd30e205de84..048fa5f356d9 100644
--- a/net/netfilter/nf_tables_offload.c
+++ b/net/netfilter/nf_tables_offload.c
@@ -233,6 +233,9 @@ bool nft_chain_offload_support(const struct nft_base_chain *basechain)
 			    ops->hooknum != NF_NETDEV_INGRESS)
 				return false;
 
+			if (!net_eq(dev_net(dev), &init_net))
+				return false;
+
 			dev = ops->dev;
 			if (!dev->netdev_ops->ndo_setup_tc &&
 			    !flow_indr_dev_exists())
diff --git a/net/sched/sch_cbs.c b/net/sched/sch_cbs.c
index 8c9a0400c862..6daa9f702a59 100644
--- a/net/sched/sch_cbs.c
+++ b/net/sched/sch_cbs.c
@@ -281,7 +281,7 @@ static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
 	struct tc_cbs_qopt_offload cbs = { };
 	int err;
 
-	if (!ops->ndo_setup_tc) {
+	if (!tc_can_offload(dev) || !ops->ndo_setup_tc) {
 		NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
 		return -EOPNOTSUPP;
 	}
diff --git a/net/sched/sch_etf.c b/net/sched/sch_etf.c
index c74d778c32a1..7801e009e025 100644
--- a/net/sched/sch_etf.c
+++ b/net/sched/sch_etf.c
@@ -323,7 +323,7 @@ static int etf_enable_offload(struct net_device *dev, struct etf_sched_data *q,
 	struct tc_etf_qopt_offload etf = { };
 	int err;
 
-	if (!ops->ndo_setup_tc) {
+	if (!tc_can_offload(dev) || !ops->ndo_setup_tc) {
 		NL_SET_ERR_MSG(extack, "Specified device does not support ETF offload");
 		return -EOPNOTSUPP;
 	}
diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index f3e5ef9a9592..d853f3b60121 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -410,7 +410,7 @@ static int mqprio_init(struct Qdisc *sch, struct nlattr *opt,
 	 * the queue mapping then run ndo_setup_tc otherwise use the
 	 * supplied and verified mapping
 	 */
-	if (qopt->hw) {
+	if (qopt->hw && tc_can_offload(dev)) {
 		err = mqprio_enable_offload(sch, qopt, extack);
 		if (err)
 			return err;
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 300d577b3286..7451d74af91f 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1522,7 +1522,7 @@ static int taprio_enable_offload(struct net_device *dev,
 	struct tc_taprio_caps caps;
 	int tc, err = 0;
 
-	if (!ops->ndo_setup_tc) {
+	if (!tc_can_offload(dev) || !ops->ndo_setup_tc) {
 		NL_SET_ERR_MSG(extack,
 			       "Device does not support taprio offload");
 		return -EOPNOTSUPP;