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

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Message-ID: <Zw5DwvIlxyL5n_T1@hog>
Date: Tue, 15 Oct 2024 12:28:18 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Jianbo Liu <jianbol@...dia.com>
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

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.

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.


> 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.

-- 
Sabrina