Re: [PATCH] scsi: mptsas: dequeue request object in case of an error (CVE-2021-3392)

[Paolo Bonzini]

On 02/02/21 14:21, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> 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.
> Unconditionally dequeue 'req' object from 's->pending' to avoid it.
>
> Fixes: CVE-2021-3392
> Buglink: https://bugs.launchpad.net/qemu/+bug/1914236
> Reported-by: Cheolwoo Myung <cwmyung@snu.ac.kr>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>   hw/scsi/mptsas.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/scsi/mptsas.c b/hw/scsi/mptsas.c
> index f86616544b..adff5b0bf2 100644
> --- a/hw/scsi/mptsas.c
> +++ b/hw/scsi/mptsas.c
> @@ -257,8 +257,8 @@ 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);
>       }
> +    QTAILQ_REMOVE(&s->pending, req, next);
>       qemu_sglist_destroy(&req->qsg);
>       g_free(req);
>   }

s->pending is not used for anything, it can just be removed.

Paolo