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

[P J P <ppandit@redhat.com>]

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);
 }
-- 
2.29.2