netdev - Re: [PATCH net v3] can: raw: fix receiver memory leak

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Date: Wed, 19 Jul 2023 07:04:56 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
Cc: Marc Kleine-Budde <mkl@...gutronix.de>, socketcan@...tkopp.net, davem@...emloft.net, 
	kuba@...nel.org, pabeni@...hat.com, linux-can@...r.kernel.org, 
	netdev@...r.kernel.org, penguin-kernel@...ove.sakura.ne.jp
Subject: Re: [PATCH net v3] can: raw: fix receiver memory leak

On Wed, Jul 19, 2023 at 6:41 AM Ziyang Xuan (William)
<william.xuanziyang@...wei.com> wrote:
>
> > On Mon, Jul 17, 2023 at 9:27 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> >>
> >> On 11.07.2023 09:17:37, Ziyang Xuan wrote:
> >>> Got kmemleak errors with the following ltp can_filter testcase:
> >>>
> >>> for ((i=1; i<=100; i++))
> >>> do
> >>>         ./can_filter &
> >>>         sleep 0.1
> >>> done
> >>>
> >>> ==============================================================
> >>> [<00000000db4a4943>] can_rx_register+0x147/0x360 [can]
> >>> [<00000000a289549d>] raw_setsockopt+0x5ef/0x853 [can_raw]
> >>> [<000000006d3d9ebd>] __sys_setsockopt+0x173/0x2c0
> >>> [<00000000407dbfec>] __x64_sys_setsockopt+0x61/0x70
> >>> [<00000000fd468496>] do_syscall_64+0x33/0x40
> >>> [<00000000b7e47d51>] entry_SYSCALL_64_after_hwframe+0x61/0xc6
> >>>
> >>> It's a bug in the concurrent scenario of unregister_netdevice_many()
> >>> and raw_release() as following:
> >>>
> >>>              cpu0                                        cpu1
> >>> unregister_netdevice_many(can_dev)
> >>>   unlist_netdevice(can_dev) // dev_get_by_index() return NULL after this
> >>>   net_set_todo(can_dev)
> >>>                                               raw_release(can_socket)
> >>>                                                 dev = dev_get_by_index(, ro->ifindex); // dev == NULL
> >>>                                                 if (dev) { // receivers in dev_rcv_lists not free because dev is NULL
> >>>                                                   raw_disable_allfilters(, dev, );
> >>>                                                   dev_put(dev);
> >>>                                                 }
> >>>                                                 ...
> >>>                                                 ro->bound = 0;
> >>>                                                 ...
> >>>
> >>> call_netdevice_notifiers(NETDEV_UNREGISTER, )
> >>>   raw_notify(, NETDEV_UNREGISTER, )
> >>>     if (ro->bound) // invalid because ro->bound has been set 0
> >>>       raw_disable_allfilters(, dev, ); // receivers in dev_rcv_lists will never be freed
> >>>
> >>> Add a net_device pointer member in struct raw_sock to record bound can_dev,
> >>> and use rtnl_lock to serialize raw_socket members between raw_bind(), raw_release(),
> >>> raw_setsockopt() and raw_notify(). Use ro->dev to decide whether to free receivers in
> >>> dev_rcv_lists.
> >>>
> >>> Fixes: 8d0caedb7596 ("can: bcm/raw/isotp: use per module netdevice notifier")
> >>> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
> >>> Reviewed-by: Oliver Hartkopp <socketcan@...tkopp.net>
> >>> Acked-by: Oliver Hartkopp <socketcan@...tkopp.net>
> >>
> >> Added to linux-can/testing.
> >>
> >
> > This patch causes three syzbot LOCKDEP reports so far.
>
> Hello Eric,
>
> Is there reproducer? I want to understand the specific root cause.
>

No repro yet, but simply look at other functions in net/can/raw.c

You must always take locks in the same order.

raw_bind(), raw_setsockopt() use:

rtnl_lock();
lock_sock(sk);

Therefore, raw_release() must _also_ use the same order, or risk deadlock.

Please build a LOCKDEP enabled kernel, and run your tests ?