net/sched: act_mirred: better wording on protection against excessive stack growth

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2150278
Upstream Status: net-next.git commit 78dcdff

commit 78dcdff
Author: Davide Caratti <dcaratti@redhat.com>
Date:   Fri Jan 20 18:01:39 2023 +0100

    net/sched: act_mirred: better wording on protection against excessive stack growth

    with commit e2ca070 ("net: sched: protect against stack overflow in
    TC act_mirred"), act_mirred protected itself against excessive stack growth
    using per_cpu counter of nested calls to tcf_mirred_act(), and capping it
    to MIRRED_RECURSION_LIMIT. However, such protection does not detect
    recursion/loops in case the packet is enqueued to the backlog (for example,
    when the mirred target device has RPS or skb timestamping enabled). Change
    the wording from "recursion" to "nesting" to make it more clear to readers.

    CC: Jamal Hadi Salim <jhs@mojatatu.com>
    Signed-off-by: Davide Caratti <dcaratti@redhat.com>
    Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
    Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

net/sched/act_mirred.c

@@ -28,8 +28,8 @@
 static LIST_HEAD(mirred_list);
 static DEFINE_SPINLOCK(mirred_list_lock);
 
-#define MIRRED_RECURSION_LIMIT    4
-static DEFINE_PER_CPU(unsigned int, mirred_rec_level);
+#define MIRRED_NEST_LIMIT    4
+static DEFINE_PER_CPU(unsigned int, mirred_nest_level);
 
 static bool tcf_mirred_is_act_redirect(int action)
 {
@@ -225,7 +225,7 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	struct sk_buff *skb2 = skb;
 	bool m_mac_header_xmit;
 	struct net_device *dev;
-	unsigned int rec_level;
+	unsigned int nest_level;
 	int retval, err = 0;
 	bool use_reinsert;
 	bool want_ingress;
@@ -236,11 +236,11 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	int mac_len;
 	bool at_nh;
 
-	rec_level = __this_cpu_inc_return(mirred_rec_level);
-	if (unlikely(rec_level > MIRRED_RECURSION_LIMIT)) {
+	nest_level = __this_cpu_inc_return(mirred_nest_level);
+	if (unlikely(nest_level > MIRRED_NEST_LIMIT)) {
 		net_warn_ratelimited("Packet exceeded mirred recursion limit on dev %s\n",
 				     netdev_name(skb->dev));
-		__this_cpu_dec(mirred_rec_level);
+		__this_cpu_dec(mirred_nest_level);
 		return TC_ACT_SHOT;
 	}
 
@@ -310,7 +310,7 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 			err = tcf_mirred_forward(res->ingress, skb);
 			if (err)
 				tcf_action_inc_overlimit_qstats(&m->common);
-			__this_cpu_dec(mirred_rec_level);
+			__this_cpu_dec(mirred_nest_level);
 			return TC_ACT_CONSUMED;
 		}
 	}
@@ -322,7 +322,7 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 		if (tcf_mirred_is_act_redirect(m_eaction))
 			retval = TC_ACT_SHOT;
 	}
-	__this_cpu_dec(mirred_rec_level);
+	__this_cpu_dec(mirred_nest_level);
 
 	return retval;
 }