netdev - Re: [PATCH net v5] net: sched: cls_u32: Fix u32's systematic failure to free IDR entries for hnodes.

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Message-ID: <Zy1qvkSHyEREU3Y1@pop-os.localdomain>
Date: Thu, 7 Nov 2024 17:34:54 -0800
From: Cong Wang <xiyou.wangcong@...il.com>
To: Alexandre Ferrieux <alexandre.ferrieux@...il.com>
Cc: edumazet@...gle.com, jhs@...atatu.com, jiri@...nulli.us,
	alexandre.ferrieux@...nge.com, netdev@...r.kernel.org
Subject: Re: [PATCH net v5] net: sched: cls_u32: Fix u32's systematic failure
 to free IDR entries for hnodes.

On Fri, Nov 08, 2024 at 12:11:23AM +0100, Alexandre Ferrieux wrote:
> 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, along with a corresponding tdc test.

Good catch! I have a few comments below.

> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Alexandre Ferrieux <alexandre.ferrieux@...nge.com>
> ---
> v5: fix title - again
> v4: add tdc test
> v3: prepend title with subsystem ident
> v2: use u32 type in handle encoder/decoder
> 
> 
>  net/sched/cls_u32.c                           | 18 ++++++++++----
>  .../tc-testing/tc-tests/filters/u32.json      | 24 +++++++++++++++++++
>  2 files changed, 38 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 9412d88a99bc..6da94b809926 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -41,6 +41,16 @@
>  #include <linux/idr.h>
>  #include <net/tc_wrapper.h>
>  
> +static inline u32 handle2id(u32 h)
> +{
> +	return ((h & 0x80000000) ? ((h >> 20) & 0x7FF) : h);
> +}
> +
> +static inline u32 id2handle(u32 id)
> +{
> +	return (id | 0x800U) << 20;
> +}
> +
>  struct tc_u_knode {
>  	struct tc_u_knode __rcu	*next;
>  	u32			handle;
> @@ -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;
>  		}

It seems you missed the idr_replace() case?

 - idr_replace(&ht->handle_idr, n, n->handle);
 + idr_replace(&ht->handle_idr, n, handle2id(n->handle));


> diff --git a/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json b/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
> index 24bd0c2a3014..2095baa19c6a 100644
> --- a/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
> +++ b/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
> @@ -329,5 +329,29 @@
>          "teardown": [
>              "$TC qdisc del dev $DEV1 parent root drr"
>          ]
> +    },
> +    {
> +        "id": "1234",
> +        "name": "Exercise IDR leaks by creating/deleting a filter many (2048) times",
> +        "category": [
> +            "filter",
> +            "u32"
> +        ],
> +        "plugins": {
> +            "requires": "nsPlugin"
> +        },
> +        "setup": [
> +            "$TC qdisc add dev $DEV1 parent root handle 10: drr",
> +            "$TC filter add dev $DEV1 parent 10:0 protocol ip prio 2 u32 match ip src 0.0.0.2/32 action drop",
> +            "$TC filter add dev $DEV1 parent 10:0 protocol ip prio 3 u32 match ip src 0.0.0.3/32 action drop"
> +        ],
> +        "cmdUnderTest": "bash -c 'for i in {1..2048} ;do $TC filter delete dev $DEV1 pref 3;$TC filter add dev $DEV1 parent 10:0 protocol ip prio 3 u32 match ip src 0.0.0.3/32 action drop || exit 1;i=`expr $i + 1`;done'",

Any reason using this for loop instead of tdc_multibatch.py?

Thanks.