linux-kernel - Re: CVE-2022-49660: xen/arm: Fix race in RB-tree based P2M accounting

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Message-ID: <9a6223ee-cb70-4c20-9749-e5ddc5018f1b@suse.com>
Date: Wed, 26 Feb 2025 08:01:04 +0100
From: Juergen Gross <jgross@...e.com>
To: cve@...nel.org, linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: CVE-2022-49660: xen/arm: Fix race in RB-tree based P2M accounting

On 26.02.25 03:23, Greg Kroah-Hartman wrote:
> Description
> ===========
> 
> In the Linux kernel, the following vulnerability has been resolved:
> 
> xen/arm: Fix race in RB-tree based P2M accounting
> 
> During the PV driver life cycle the mappings are added to
> the RB-tree by set_foreign_p2m_mapping(), which is called from
> gnttab_map_refs() and are removed by clear_foreign_p2m_mapping()
> which is called from gnttab_unmap_refs(). As both functions end
> up calling __set_phys_to_machine_multi() which updates the RB-tree,
> this function can be called concurrently.
> 
> There is already a "p2m_lock" to protect against concurrent accesses,
> but the problem is that the first read of "phys_to_mach.rb_node"
> in __set_phys_to_machine_multi() is not covered by it, so this might
> lead to the incorrect mappings update (removing in our case) in RB-tree.
> 
> In my environment the related issue happens rarely and only when
> PV net backend is running, the xen_add_phys_to_mach_entry() claims
> that it cannot add new pfn <-> mfn mapping to the tree since it is
> already exists which results in a failure when mapping foreign pages.
> 
> But there might be other bad consequences related to the non-protected
> root reads such use-after-free, etc.
> 
> While at it, also fix the similar usage in __pfn_to_mfn(), so
> initialize "struct rb_node *n" with the "p2m_lock" held in both
> functions to avoid possible bad consequences.
> 
> This is CVE-2022-33744 / XSA-406.

As clearly visible in the commit message: there is already a CVE assigned.

Please revoke CVE-2022-49660.


Juergen

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