linux-kernel - Re: [Question] SCSI_EH: How does EH guarantee there is no UAF of scsi

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Date:   Thu, 21 Apr 2022 23:24:36 +0800
From:   Wenchao Hao <haowenchao@...wei.com>
To:     Hannes Reinecke <hare@...e.de>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Feilong Lin <linfeilong@...wei.com>
Subject: Re: [Question] SCSI_EH: How does EH guarantee there is no UAF of
 scsi_cmnd if host reset failed


On 2022/4/19 22:56, Hannes Reinecke wrote:
> On 4/19/22 16:28, Wenchao Hao wrote:
>> Hi all, I am wondered how does SCSI EH guarantee there is no UAF of scsi_cmnd
>> if host reset failed. If host reset failed and eh_cmd_q of shost is not empty,
>> these command in eh_cmd_q would be added to done_q in scsi_eh_offline_sdevs()
>> and finished by scsi_eh_flush_done_q(). So these scsi_cmnd and it's related
>> request would be freed.
>>
> Yes.
> 
>> While since host reset failed, we can not guarantee the LLDDs has cleared all
>> references to these commands in eh_cmd_q. Is there any possibility that the
>> LLDDs reference to these commands? If this happened, then a using after free
>> issue would occur.
>>
> If host reset has failed there are _no_ assumptions we can make about commands, and not even about the PCI device itself.
> So in effect, once host_reset failed the system is hosed.
> 
> We _might_ be able to resurrect the system by doing PCI EEH, but not many systems nor drivers implement that.
> 
> Cheers,
> 
> Hannes
> 
> .

Thanks a lot for your reply. I am writing single LUN reset EH flow which discussed in previous mail
and testing it, if the test result is good I would post it.

By the way, you said you would make EH rework, are you doing it? Could you tell us your plan
if it's not secret.