netdev - Re: [PATCH net] net: avoid potential UAF in default

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Message-ID: <20241204125717.6wxa4llwpdhv5hon@skbuf>
Date: Wed, 4 Dec 2024 14:57:17 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, eric.dumazet@...il.com,
	syzbot+1939f24bdb783e9e43d9@...kaller.appspotmail.com
Subject: Re: [PATCH net] net: avoid potential UAF in default_operstate()

On Wed, Dec 04, 2024 at 12:46:11PM +0100, Eric Dumazet wrote:
> On Wed, Dec 4, 2024 at 12:41â€¯PM Vladimir Oltean <vladimir.oltean@....com> wrote:
> >
> > I meant: linkwatch runs periodically, via linkwatch_event(). Isn't there
> > a chance that linkwatch_event() can run once, immediately after
> > __rtnl_unlock() in netdev_run_todo(), while the netdev is in the
> > NETREG_UNREGISTERING state? Won't that create problems for __dev_get_by_index()
> > too? I guess it depends on when the netns is torn down, which I couldn't find.
> 
> I think lweventlist_lock and dev->link_watch_list are supposed to
> synchronize things.
> 
> linkwatch_sync_dev() only calls linkwatch_do_dev() if the device was
> atomically unlinked from lweventlist

No, I don't mean calls from linkwatch_sync_dev(). I mean other call
paths towards linkwatch_do_dev(), like for example linkwatch_fire_event() -
carrier down, whatever. Can't these be pending on an unregistering
net_device at the time we run __rtnl_unlock() in netdev_run_todo?
Otherwise, why would netdev_wait_allrefs_any() have a linkwatch_run_queue()
call just later?