Re: [PATCH-for-6.0?] mptsas: remove unused MPTSASState.pending (CVE-2021-3392)

[Philippe Mathieu-Daudé]

On 4/16/21 1:33 PM, Philippe Mathieu-Daudé wrote:
> Cc'ing maintainers.
> 
> On 4/16/21 1:27 PM, Philippe Mathieu-Daudé wrote:
>> On 4/16/21 12:22 PM, Michael Tokarev wrote:
>>> During previous attempt to fix CVE-2021-3392 it was discovered
>>> that MPTSASState.pending is actually not used. So instead of
>>> fixing the prob, just remove the offending code entirely
>>
>> What problem?

Digging a bit I found:
https://bugs.launchpad.net/qemu/+bug/1914236
and Paolo's comment:
https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg02660.html

So your patch now makes sense, but please:

1/ Reword including Prasad description:

"""
While processing SCSI i/o requests in mptsas_process_scsi_io_request(),
the Megaraid emulator appends new MPTSASRequest object 'req' to
the 's->pending' queue. In case of an error, this same object gets
dequeued in mptsas_free_request() only if SCSIRequest object
'req->sreq' is initialised. This may lead to a use-after-free issue.

Since MPTSASState.pending is actually not used, simply remove it.
"""

2/ Add:

BugLink: https://bugs.launchpad.net/qemu/+bug/1914236 (CVE-2021-3392)
Fixes: e351b826112 ("hw: Add support for LSI SAS1068 (mptsas) device")

With it:
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

>>> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
>>> Cc: Prasad J Pandit <pjp@fedoraproject.org>
>>> Cc: qemu-stable@nongnu.org
>>> ---
>>>  hw/scsi/mptsas.c | 4 ----
>>>  hw/scsi/mptsas.h | 1 -
>>>  2 files changed, 5 deletions(-)
>>>
>>> diff --git a/hw/scsi/mptsas.c b/hw/scsi/mptsas.c
>>> index 7416e78706..5abbc742aa 100644
>>> --- a/hw/scsi/mptsas.c
>>> +++ b/hw/scsi/mptsas.c
>>> @@ -257,7 +257,6 @@ static void mptsas_free_request(MPTSASRequest *req)
>>>          req->sreq->hba_private = NULL;
>>>          scsi_req_unref(req->sreq);
>>>          req->sreq = NULL;
>>> -        QTAILQ_REMOVE(&s->pending, req, next);
>>>      }
>>>      qemu_sglist_destroy(&req->qsg);
>>>      g_free(req);
>>> @@ -303,7 +302,6 @@ static int mptsas_process_scsi_io_request(MPTSASState 
>>> *s,
>>>      }
>>>  
>>>      req = g_new0(MPTSASRequest, 1);
>>> -    QTAILQ_INSERT_TAIL(&s->pending, req, next);
>>>      req->scsi_io = *scsi_io;
>>>      req->dev = s;
>>>  
>>> @@ -1319,8 +1317,6 @@ static void mptsas_scsi_realize(PCIDevice *dev, Error 
>>> **errp)
>>>  
>>>      s->request_bh = qemu_bh_new(mptsas_fetch_requests, s);
>>>  
>>> -    QTAILQ_INIT(&s->pending);
>>> -
>>>      scsi_bus_new(&s->bus, sizeof(s->bus), &dev->qdev, &mptsas_scsi_info, 
>>> NULL);
>>>  }
>>>  
>>> diff --git a/hw/scsi/mptsas.h b/hw/scsi/mptsas.h
>>> index b85ac1a5fc..c046497db7 100644
>>> --- a/hw/scsi/mptsas.h
>>> +++ b/hw/scsi/mptsas.h
>>> @@ -79,7 +79,6 @@ struct MPTSASState {
>>>      uint16_t reply_frame_size;
>>>  
>>>      SCSIBus bus;
>>> -    QTAILQ_HEAD(, MPTSASRequest) pending;
>>>  };
>>>  
>>>  void mptsas_fix_scsi_io_endianness(MPIMsgSCSIIORequest *req);
>>>
>>
>