netdev - Re: [PATCH net] macsec: Fix use-after-free while sending the offloading packet

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Message-ID: <ded4f325-e83d-4b34-b96c-656fc3c0845f@nvidia.com>
Date: Tue, 15 Oct 2024 21:46:26 +0800
From: Jianbo Liu <jianbol@...dia.com>
To: Sabrina Dubroca <sd@...asysnail.net>
CC: Tariq Toukan <tariqt@...dia.com>, "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Eric
 Dumazet" <edumazet@...gle.com>, <netdev@...r.kernel.org>, Saeed Mahameed
	<saeedm@...dia.com>, Gal Pressman <gal@...dia.com>, Leon Romanovsky
	<leonro@...dia.com>, Patrisious Haddad <phaddad@...dia.com>, Chris Mi
	<cmi@...dia.com>
Subject: Re: [PATCH net] macsec: Fix use-after-free while sending the
 offloading packet



On 10/15/2024 6:28 PM, Sabrina Dubroca wrote:
> 2024-10-15, 17:57:59 +0800, Jianbo Liu wrote:
>>
>>
>> On 10/15/2024 4:56 PM, Sabrina Dubroca wrote:
>>> 2024-10-14, 12:07:20 +0300, Tariq Toukan wrote:
>>>> From: Jianbo Liu <jianbol@...dia.com>
>>>>
>>>> KASAN reports the following UAF. The metadata_dst, which is used to
>>>> store the SCI value for macsec offload, is already freed by
>>>> metadata_dst_free() in macsec_free_netdev(), while driver still use it
>>>> for sending the packet.
>>>>
>>>> To fix this issue, dst_release() is used instead to release
>>>> metadata_dst. So it is not freed instantly in macsec_free_netdev() if
>>>> still referenced by skb.
>>>
>>> Ok. Then that packet is going to get dropped when it reaches the
>>> driver, right? At this point the TXSA we need shouldn't be configured
>>
>> I think so because dst's output should be updated.
> 
> What updates the dst when we're deleting the macsec device? And this
> is just a metadata_dst, it's only useful to hold the SCI.
> 

You are right. It's not updated.

> But I guess we would have the same issue when the macsec device still
> exists but the TXSA is gone, so hopefully this is handled well by all
> drivers.
> 

And for now, I'd rather focus on fixing the kernel crash caused by UAF.

> 
>> But the problem here is
>> dst free is delayed by RCU, which causes UAF.
> 
> To be clear, I'm not objecting to the patch, I'm wondering about other
> related issues once we fix that.

OK. I will send v2 later.

Thanks!
Jianbo

>