Re: [PATCH] xen/events: avoid NULL pointer dereference in evtchn_from_irq()

[Boris Ostrovsky]

On 5/21/20 2:46 PM, Marek Marczykowski-GÃrecki wrote:
> On Thu, May 21, 2020 at 01:22:03PM -0400, Boris Ostrovsky wrote:
>> On 3/19/20 3:14 AM, Juergen Gross wrote:
>>> There have been reports of races in evtchn_from_irq() where the info
>>> pointer has been NULL.
>>>
>>> Avoid that case by testing info before dereferencing it.
>>>
>>> In order to avoid accessing a just freed info structure do the kfree()
>>> via kfree_rcu().
>>
>> Looks like noone ever responded to this.
>>
>>
>> This change looks fine but is there a background on the problem? I
>> looked in the archives and didn't find the relevant discussion.
> Here is the original bug report:
> https://xen.markmail.org/thread/44apwkwzeme4uavo
>


Thanks. Do we know what the race is? Is it because an event is being
delivered from a dying guest who is in the process of tearing down event
channels?


-boris