linux-kernel - Re: [PATCH] net: sched: fix a use-after-free error on chain on the error exit path

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Message-ID: <20170520071315.GB1833@nanopsycho>
Date:   Sat, 20 May 2017 09:13:15 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Colin King <colin.king@...onical.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "David S . Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: sched: fix a use-after-free error on chain on the
 error exit path

Fri, May 19, 2017 at 07:17:59PM CEST, xiyou.wangcong@...il.com wrote:
>On Thu, May 18, 2017 at 7:07 AM, Colin King <colin.king@...onical.com> wrote:
>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>> index 4020b8d932a1..82ebdc3fcb2e 100644
>> --- a/net/sched/cls_api.c
>> +++ b/net/sched/cls_api.c
>> @@ -511,6 +511,7 @@ static int tc_ctl_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
>>         if (n->nlmsg_type == RTM_DELTFILTER && prio == 0) {
>>                 tfilter_notify_chain(net, skb, n, chain, RTM_DELTFILTER);
>>                 tcf_chain_destroy(chain);
>
>
>Jiri, how does this work...? An action could hold a refcnt to a filter
>chain, but here you destroy a whole chain without respecting
>the refcnt???

Correct. I missed this. Will fix, thanks.


>
>
>> +               chain = NULL;
>>                 err = 0;
>>                 goto errout;
>
>Colin, not your fault, I think we may miss something more serious
>when reviewing Jiri's patchset. ;)
>
>Thanks.