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

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Message-ID: <20240828170657.5f493cc6@kernel.org>
Date: Wed, 28 Aug 2024 17:06:57 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jeongjun Park <aha310510@...il.com>
Cc: Paolo Abeni <pabeni@...hat.com>, wei.liu@...nel.org, paul@....org,
 davem@...emloft.net, edumazet@...gle.com, 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 Wed, 28 Aug 2024 21:52:12 +0900 Jeongjun Park wrote:
> > The loop runs with irq disabled, the RCU critical section extends over
> > it, uninterrupted.  
> 
> Basically, list_for_each_entry_rcu is specified to be used under the protection
> of rcu_read_lock(), but this is not the case with xenvif_new_hash(). If it is
> used without the protection of rcu_read_lock(), kfree is called immediately
> after the grace period ends after the call to kfree_rcu() inside
> list_for_each_entry_rcu, so the entry is released, and a UAF occurs when
> fetching with ->next thereafter.

You cut off and didn't answer Paolo's question whether you have a splat
/ saw this actually cause a crash or a KASAN warning.