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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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>
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);
 }
 
-- 
2.26.3