[PATCH 3.16 291/370] scsi: zfcp: fix use-after-free by not tracing WKA port open/close on failed send

Ben Hutchings
2017-03-10T13:23:46Z

From: Steffen Maier <maier@linux.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@oracle.com>
Suggested-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Fixes: d27a7cb91960 ("zfcp: trace on request for open and close of WKA port")
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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
@@ -1584,7 +1584,7 @@ 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);
@@ -1613,7 +1613,7 @@ 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;
}
@@ -1639,7 +1639,7 @@ 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);
@@ -1668,7 +1668,7 @@ 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;
}