Re: [PATCH-for-6.0? v2] mptsas: Remove unused MPTSASState 'pending' field (CVE-2021-3392)

[Philippe Mathieu-Daudé]

On 4/18/21 7:30 AM, Philippe Mathieu-Daudé wrote:
> From: Michael Tokarev <mjt@tls.msk.ru>
> 
> 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 s->pending is actually not used, simply remove it from
> MPTSASState.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> Message-Id: <20210416102243.1293871-1-mjt@msgid.tls.msk.ru>

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>

> Reported-by: Cheolwoo Myung <cwmyung@snu.ac.kr>
> BugLink: https://bugs.launchpad.net/qemu/+bug/1914236 (CVE-2021-3392)
> Fixes: e351b826112 ("hw: Add support for LSI SAS1068 (mptsas) device")
> [PMD: Reworded description, added more tags]
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
> Supersedes: <20210416102243.1293871-1-mjt@msgid.tls.msk.ru>
> 
> MJT patch:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg799236.html
> 
> Since rc4 is soon, I'm directly respining his patch with my comments
> addressed.
> 
> This is not a new regression (present since QEMU v2.6.0) but is a
> CVE...
> 
> PJP first patch:
> https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg02660.html
> ---
>  hw/scsi/mptsas.h | 1 -
>  hw/scsi/mptsas.c | 4 ----
>  2 files changed, 5 deletions(-)
> 
> diff --git a/hw/scsi/mptsas.h b/hw/scsi/mptsas.h
> index b85ac1a5fcc..c046497db71 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);
> diff --git a/hw/scsi/mptsas.c b/hw/scsi/mptsas.c
> index 7416e787061..5abbc742aaf 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);
>  }
>  
>