linux-kernel - Re: [PATCH net] net/xen-netback: prevent UAF in xenvif_flush

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Message-ID: <fd2a06d5-370f-4e07-af84-cab089b82a4b@redhat.com>
Date: Tue, 27 Aug 2024 13:19:59 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Jeongjun Park <aha310510@...il.com>, wei.liu@...nel.org, paul@....org
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 madhuparnabhowmik04@...il.com, xen-devel@...ts.xenproject.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/xen-netback: prevent UAF in xenvif_flush_hash()

On 8/22/24 20:11, Jeongjun Park wrote:
> During the list_for_each_entry_rcu iteration call of xenvif_flush_hash,
> kfree_rcu does not exist inside the rcu read critical section, so if

The above wording is confusing, do you mean "kfree_rcu does not exit 
from "...?

> kfree_rcu is called when the rcu grace period ends during the iteration,
> UAF occurs when accessing head->next after the entry becomes free.

The loop runs with irq disabled, the RCU critical section extends over 
it, uninterrupted.

Do you have a splat for the reported UAF?

This does not look the correct solution.

Thanks,

Paolo