linux-kernel - Re: [PATCH net] net: fix NULL pointer dereference in l3mdev_l3

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Message-ID: <d824f621-bae1-4b79-a4c6-620aeecc1bb0@huawei.com>
Date: Fri, 21 Mar 2025 16:51:03 +0800
From: Wang Liang <wangliang74@...wei.com>
To: Simon Horman <horms@...nel.org>
CC: David Ahern <dsahern@...nel.org>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<fw@...len.de>, <daniel@...earbox.net>, <yuehaibing@...wei.com>,
	<zhangchangzhong@...wei.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: fix NULL pointer dereference in l3mdev_l3_rcv


在 2025/3/20 21:37, Simon Horman 写道:
> On Wed, Mar 19, 2025 at 10:07:03AM +0800, Wang Liang wrote:
>> 在 2025/3/18 23:02, David Ahern 写道:
>>> On 3/18/25 3:38 PM, Simon Horman wrote:
>>>> On Thu, Mar 13, 2025 at 09:27:13AM +0800, Wang Liang wrote:
>>>>> When delete l3s ipvlan:
>>>>>
>>>>>       ip link del link eth0 ipvlan1 type ipvlan mode l3s
>>>>>
>>>>> This may cause a null pointer dereference:
>>>>>
>>>>>       Call trace:
>>>>>        ip_rcv_finish+0x48/0xd0
>>>>>        ip_rcv+0x5c/0x100
>>>>>        __netif_receive_skb_one_core+0x64/0xb0
>>>>>        __netif_receive_skb+0x20/0x80
>>>>>        process_backlog+0xb4/0x204
>>>>>        napi_poll+0xe8/0x294
>>>>>        net_rx_action+0xd8/0x22c
>>>>>        __do_softirq+0x12c/0x354
>>>>>
>>>>> This is because l3mdev_l3_rcv() visit dev->l3mdev_ops after
>>>>> ipvlan_l3s_unregister() assign the dev->l3mdev_ops to NULL. The process
>>>>> like this:
>>>>>
>>>>>       (CPU1)                     | (CPU2)
>>>>>       l3mdev_l3_rcv()            |
>>>>>         check dev->priv_flags:   |
>>>>>           master = skb->dev;     |
>>>>>                                  |
>>>>>                                  | ipvlan_l3s_unregister()
>>>>>                                  |   set dev->priv_flags
>>>>>                                  |   dev->l3mdev_ops = NULL;
>>>>>                                  |
>>>>>         visit master->l3mdev_ops |
>>>>>
>>>>> Add lock for dev->priv_flags and dev->l3mdev_ops is too expensive. Resolve
>>>>> this issue by add check for master->l3mdev_ops.
>>>> Hi Wang Liang,
>>>>
>>>> It seems to me that checking master->l3mdev_ops like this is racy.
>>> vrf device leaves the l3mdev ops set; that is probably the better way to go.
>> Thanks.
>>
>> Only l3s ipvlan set the dev->l3mdev_ops to NULL at present, I will delete
>> 'dev->l3mdev_ops = NULL' in ipvlan_l3s_unregister(), is that ok?
> TBH, I am somewhat unclear on the correct tear down behaviour.
> But I also understood that to be David's suggestion.
> And I think that implementing that, and posting it as v2 would
> be a good next step.
Ok. I will send a patch v2 later, please check it.
Thanks.