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From:   Hawkins Jiawei <yin31149@gmail.com>
To:     kuba@kernel.org
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Subject: Re: [PATCH v2] net: sched: fix memory leak in tcindex_set_parms
Date:   Wed, 16 Nov 2022 15:35:22 +0800
Message-Id: <20221116073522.80304-1-yin31149@gmail.com>
In-Reply-To: <20221115090237.5d5988bb@kernel.org>
References: <20221115090237.5d5988bb@kernel.org>
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Hi,

On Wed, 16 Nov 2022 at 01:02, Jakub Kicinski <kuba@kernel.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.