netdev - Re: [PATCH 09/14] net: sched: don't release reference on action overwrite

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Date:   Wed, 16 May 2018 10:47:32 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        kadlec@...ckhole.kfki.hu, fw@...len.de, ast@...nel.org,
        daniel@...earbox.net, edumazet@...gle.com, keescook@...omium.org,
        linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, kliteyn@...lanox.com
Subject: Re: [PATCH 09/14] net: sched: don't release reference on action overwrite


On Wed 16 May 2018 at 07:43, Jiri Pirko <jiri@...nulli.us> wrote:
> Mon, May 14, 2018 at 04:27:10PM CEST, vladbu@...lanox.com wrote:
>>Return from action init function with reference to action taken,
>>even when overwriting existing action.
>>
>>Action init API initializes its fourth argument (pointer to pointer to
>>tc action) to either existing action with same index or newly created
>>action. In case of existing index(and bind argument is zero), init
>>function returns without incrementing action reference counter. Caller
>>of action init then proceeds working with action without actually
>>holding reference to it. This means that action could be deleted
>>concurrently. To prevent such scenario this patch changes action init
>
> Be imperative to the codebase in the patch description.
>
>
>>behavior to always take reference to action before returning
>>successfully.
>
> Where's the balance? Who does the release instead? I'm probably missing
> something.

I've resplit these patches for V2 to always do take/release in same
patch.

>
>>
>>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
>>---
>> net/sched/act_bpf.c        |  8 ++++----
>> net/sched/act_connmark.c   |  5 +++--
>> net/sched/act_csum.c       |  8 ++++----
>> net/sched/act_gact.c       |  5 +++--
>> net/sched/act_ife.c        | 12 +++++-------
>> net/sched/act_ipt.c        |  5 +++--
>> net/sched/act_mirred.c     |  5 ++---
>> net/sched/act_nat.c        |  5 +++--
>> net/sched/act_pedit.c      |  5 +++--
>> net/sched/act_police.c     |  8 +++-----
>> net/sched/act_sample.c     |  8 +++-----
>> net/sched/act_simple.c     |  5 +++--
>> net/sched/act_skbedit.c    |  5 +++--
>> net/sched/act_skbmod.c     |  8 +++-----
>> net/sched/act_tunnel_key.c |  8 +++-----
>> net/sched/act_vlan.c       |  8 +++-----
>> 16 files changed, 51 insertions(+), 57 deletions(-)
>>
>>diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
>>index 5d95c43..5554bf7 100644
>>--- a/net/sched/act_bpf.c
>>+++ b/net/sched/act_bpf.c
>>@@ -311,9 +311,10 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
>> 		if (bind)
>> 			return 0;
>> 
>>-		tcf_idr_release(*act, bind);
>>-		if (!replace)
>>+		if (!replace) {
>>+			tcf_idr_release(*act, bind);
>> 			return -EEXIST;
>>+		}
>> 	}
>> 
>> 	is_bpf = tb[TCA_ACT_BPF_OPS_LEN] && tb[TCA_ACT_BPF_OPS];
>
> [...]