linux-kernel - Re: [PATCH v2] net: sched: fix memory leak in tcindex_set

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Date:   Wed, 16 Nov 2022 15:35:22 +0800
From:   Hawkins Jiawei <yin31149@...il.com>
To:     kuba@...nel.org
Cc:     18801353760@....com, cong.wang@...edance.com, davem@...emloft.net,
        edumazet@...gle.com, jhs@...atatu.com, jiri@...nulli.us,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        pabeni@...hat.com,
        syzbot+232ebdbd36706c965ebf@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com, xiyou.wangcong@...il.com,
        yin31149@...il.com
Subject: Re: [PATCH v2] net: sched: fix memory leak in tcindex_set_parms

Hi,

On Wed, 16 Nov 2022 at 01:02, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 14 Nov 2022 01:05:08 +0800 Hawkins Jiawei wrote:
> > diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
> > index 1c9eeb98d826..d2fac9559d3e 100644
> > --- a/net/sched/cls_tcindex.c
> > +++ b/net/sched/cls_tcindex.c
> > @@ -338,6 +338,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
> >       struct tcf_result cr = {};
> >       int err, balloc = 0;
> >       struct tcf_exts e;
> > +     struct tcf_exts old_e = {};
>
> This is not a valid way of initializing a structure.
> tcf_exts_init() is supposed to be called.
> If we add a list member to that structure this code will break, again.

Yes, you are right. But the `old_e` variable here is used only for freeing
old_r->exts resource, `old_e` will be overwritten by old_r->exts content
as follows:

    struct tcf_exts old_e = {};
    ...

    if (old_r && old_r != r) {
            old_e = old_r->exts;
            ...
    }
    ...
    synchronize_rcu();
    tcf_exts_destroy(&old_e);

So this patch uses `struct tcf_exts old_e = {}` here just for a cleared space.