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

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Date:   Fri, 19 May 2017 10:17:59 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        "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

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???


> +               chain = NULL;
>                 err = 0;
>                 goto errout;

Colin, not your fault, I think we may miss something more serious
when reviewing Jiri's patchset. ;)

Thanks.