linux-kernel - [PATCH 4.9 40/60] scsi: zfcp: fix use-after-free by not tracing WKA port open/close on failed send

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Message-Id: <20170213130338.661836303@linuxfoundation.org>
Date:   Mon, 13 Feb 2017 05:04:12 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        Benjamin Block <bblock@...ux.vnet.ibm.com>,
        Steffen Maier <maier@...ux.vnet.ibm.com>,
        Jens Remus <jremus@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: [PATCH 4.9 40/60] scsi: zfcp: fix use-after-free by not tracing WKA port open/close on failed send

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steffen Maier <maier@...ux.vnet.ibm.com>

commit 2dfa6688aafdc3f74efeb1cf05fb871465d67f79 upstream.

Dan Carpenter kindly reported:
<quote>
The patch d27a7cb91960: "zfcp: trace on request for open and close of
WKA port" from Aug 10, 2016, leads to the following static checker
warning:

	drivers/s390/scsi/zfcp_fsf.c:1615 zfcp_fsf_open_wka_port()
	warn: 'req' was already freed.

drivers/s390/scsi/zfcp_fsf.c
  1609          zfcp_fsf_start_timer(req, ZFCP_FSF_REQUEST_TIMEOUT);
  1610          retval = zfcp_fsf_req_send(req);
  1611          if (retval)
  1612                  zfcp_fsf_req_free(req);
                                          ^^^
Freed.

  1613  out:
  1614          spin_unlock_irq(&qdio->req_q_lock);
  1615          if (req && !IS_ERR(req))
  1616                  zfcp_dbf_rec_run_wka("fsowp_1", wka_port, req->req_id);
                                                                  ^^^^^^^^^^^
Use after free.

  1617          return retval;
  1618  }

Same thing for zfcp_fsf_close_wka_port() as well.
</quote>

Rather than relying on req being NULL (or ERR_PTR) for all cases where
we don't want to trace or should not trace,
simply check retval which is unconditionally initialized with -EIO != 0
and it can only become 0 on successful retval = zfcp_fsf_req_send(req).
With that we can also remove the then again unnecessary unconditional
initialization of req which was introduced with that earlier commit.

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Suggested-by: Benjamin Block <bblock@...ux.vnet.ibm.com>
Signed-off-by: Steffen Maier <maier@...ux.vnet.ibm.com>
Fixes: d27a7cb91960 ("zfcp: trace on request for open and close of WKA port")
Reviewed-by: Benjamin Block <bblock@...ux.vnet.ibm.com>
Reviewed-by: Jens Remus <jremus@...ux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/s390/scsi/zfcp_fsf.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/s390/scsi/zfcp_fsf.c
+++ b/drivers/s390/scsi/zfcp_fsf.c
@@ -1583,7 +1583,7 @@ out:
 int zfcp_fsf_open_wka_port(struct zfcp_fc_wka_port *wka_port)
 {
 	struct zfcp_qdio *qdio = wka_port->adapter->qdio;
-	struct zfcp_fsf_req *req = NULL;
+	struct zfcp_fsf_req *req;
 	int retval = -EIO;
 
 	spin_lock_irq(&qdio->req_q_lock);
@@ -1612,7 +1612,7 @@ int zfcp_fsf_open_wka_port(struct zfcp_f
 		zfcp_fsf_req_free(req);
 out:
 	spin_unlock_irq(&qdio->req_q_lock);
-	if (req && !IS_ERR(req))
+	if (!retval)
 		zfcp_dbf_rec_run_wka("fsowp_1", wka_port, req->req_id);
 	return retval;
 }
@@ -1638,7 +1638,7 @@ static void zfcp_fsf_close_wka_port_hand
 int zfcp_fsf_close_wka_port(struct zfcp_fc_wka_port *wka_port)
 {
 	struct zfcp_qdio *qdio = wka_port->adapter->qdio;
-	struct zfcp_fsf_req *req = NULL;
+	struct zfcp_fsf_req *req;
 	int retval = -EIO;
 
 	spin_lock_irq(&qdio->req_q_lock);
@@ -1667,7 +1667,7 @@ int zfcp_fsf_close_wka_port(struct zfcp_
 		zfcp_fsf_req_free(req);
 out:
 	spin_unlock_irq(&qdio->req_q_lock);
-	if (req && !IS_ERR(req))
+	if (!retval)
 		zfcp_dbf_rec_run_wka("fscwp_1", wka_port, req->req_id);
 	return retval;
 }