net: sched: cls_u32: Fix u32's systematic failure to free IDR entries for hnodes.

To generate hnode handles (in gen_new_htid()), u32 uses IDR and
encodes the returned small integer into a structured 32-bit
word. Unfortunately, at disposal time, the needed decoding
is not done. As a result, idr_remove() fails, and the IDR
fills up. Since its size is 2048, the following script ends up
with "Filter already exists":

  tc filter add dev myve $FILTER1
  tc filter add dev myve $FILTER2
  for i in {1..2048}
  do
    echo $i
    tc filter del dev myve $FILTER2
    tc filter add dev myve $FILTER2
  done

This patch adds the missing decoding logic for handles that
deserve it.

Fixes: e761437 ("net_sched: use idr to allocate u32 filter handles")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Alexandre Ferrieux <alexandre.ferrieux@orange.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20241110172836.331319-1-alexandre.ferrieux@orange.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: ferrieux

net/sched/cls_u32.c

@@ -92,6 +92,16 @@ struct tc_u_common {
 	long			knodes;
 };
 
+static u32 handle2id(u32 h)
+{
+	return ((h & 0x80000000) ? ((h >> 20) & 0x7FF) : h);
+}
+
+static u32 id2handle(u32 id)
+{
+	return (id | 0x800U) << 20;
+}
+
 static inline unsigned int u32_hash_fold(__be32 key,
 					 const struct tc_u32_sel *sel,
 					 u8 fshift)
@@ -310,7 +320,7 @@ static u32 gen_new_htid(struct tc_u_common *tp_c, struct tc_u_hnode *ptr)
 	int id = idr_alloc_cyclic(&tp_c->handle_idr, ptr, 1, 0x7FF, GFP_KERNEL);
 	if (id < 0)
 		return 0;
-	return (id | 0x800U) << 20;
+	return id2handle(id);
 }
 
 static struct hlist_head *tc_u_common_hash;
@@ -360,7 +370,7 @@ static int u32_init(struct tcf_proto *tp)
 		return -ENOBUFS;
 
 	refcount_set(&root_ht->refcnt, 1);
-	root_ht->handle = tp_c ? gen_new_htid(tp_c, root_ht) : 0x80000000;
+	root_ht->handle = tp_c ? gen_new_htid(tp_c, root_ht) : id2handle(0);
 	root_ht->prio = tp->prio;
 	root_ht->is_root = true;
 	idr_init(&root_ht->handle_idr);
@@ -612,7 +622,7 @@ static int u32_destroy_hnode(struct tcf_proto *tp, struct tc_u_hnode *ht,
 		if (phn == ht) {
 			u32_clear_hw_hnode(tp, ht, extack);
 			idr_destroy(&ht->handle_idr);
-			idr_remove(&tp_c->handle_idr, ht->handle);
+			idr_remove(&tp_c->handle_idr, handle2id(ht->handle));
 			RCU_INIT_POINTER(*hn, ht->next);
 			kfree_rcu(ht, rcu);
 			return 0;
@@ -989,7 +999,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
 
 		err = u32_replace_hw_hnode(tp, ht, userflags, extack);
 		if (err) {
-			idr_remove(&tp_c->handle_idr, handle);
+			idr_remove(&tp_c->handle_idr, handle2id(handle));
 			kfree(ht);
 			return err;
 		}