netdev - Re: [PATCH] net: sched: fix memory leak in tcindex_set

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Date:   Thu, 3 Nov 2022 19:23:08 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Hawkins Jiawei <yin31149@...il.com>
Cc:     18801353760@....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
Subject: Re: [PATCH] net: sched: fix memory leak in tcindex_set_parms

On Fri,  4 Nov 2022 00:07:00 +0800 Hawkins Jiawei wrote:
> > Can't you localize all the changes to this if block?
> >
> > Maybe add a function called tcindex_filter_result_reinit()
> > which will act more appropriately?  
> 
> I think we shouldn't put the tcf_exts_destroy(&old_e)
> into this if block, or other RCU readers may derefer the
> freed memory (Please correct me If I am wrong).
> 
> So I put the tcf_exts_destroy(&old_e) near the tcindex 
> destroy work, after the RCU updateing.

I'm not sure what this code is trying to do, to be honest.
Your concern that there may be a concurrent reader is valid,
but then again tcindex_filter_result_init() just wipes the
entire structure with a memset() so concurrent readers are
already likely broken?

Maybe tcindex_filter_result_init() dates back to times when
exts were a list (see commit 22dc13c837c) and calling 
tcf_exts_init() wasn't that different than cleaning it up?
In other words this code is trying to destroy old_r, not
reinitialize it?

> >  
> > >               err = tcindex_filter_result_init(old_r, cp, net);