netdev - Re: [PATCH] netlink: fix memory leak of dump

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Date:   Mon, 23 Jul 2018 11:47:42 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Florian Westphal <fw@...len.de>
Cc:     David Miller <davem@...emloft.net>, cscnull@...il.com,
        kadlec@...ckhole.kfki.hu, johannes.berg@...el.com, Jason@...c4.com,
        ktkhai@...tuozzo.com, lucien.xin@...il.com,
        xiyou.wangcong@...il.com, dsahern@...il.com,
        netfilter-devel@...r.kernel.org, tom@...ntonium.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netlink: fix memory leak of dump

On Mon, Jul 23, 2018 at 11:42:28AM +0200, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@...filter.org> wrote:
> > > As David pointed out, once ->start() returns 0 we set cb_running, i.e.
> > > only after successful ->start() netlink core will call ->dump() again.
> > > 
> > > So I see no problem setting ->data to onstack cookie and then
> > > duplicating it to heap via kmemdup in ->start().
> > > 
> > > As far as I can see netlink core offers all functionality already,
> > > so we only need to switch netfilter to make use of it.
> > > 
> > > If you disagree please let me know, otherwise I will cook up
> > > a patch along this pattern for net/netfilter/*.
> > 
> > Why not just call ->done from netlink_dump_start() when it fails?
> 
> Not sure thats safe for all users, we will also still need to call
> it in nft_netlink_dump_start and we need to play guess game wrt
> EINTR (which can mean 'dump was now started, do not send ack').

We can also add another scratchpad area, similar to the ->cb[x] area
that can be initialized before netlink_dump_start()? So we don't need
the data pointer.

By passing the array of attributes, we'll need to do attribute parsing
over and over again from each netlink_dump() call.