rapidio: avoid data race between file operation callbacks and mport_cdev_add().

Fields of md(mport_dev) are set after cdev_device_add().  However, the
file operation callbacks can be called after cdev_device_add() and
therefore accesses to fields of md in the callbacks can race with the rest
of the mport_cdev_add() function.

One such example is INIT_LIST_HEAD(&md->portwrites) in mport_cdev_add(),
the list is initialised after cdev_device_add().  This can race with
list_add_tail(&pw_filter->md_node,&md->portwrites) in
rio_mport_add_pw_filter() which is called by unlocked_ioctl.

To avoid such data races use cdev_device_add() after initializing md.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Allison Randal <allison@lohutok.net>
Cc: Pavel Andrianov <andrianov@ispras.ru>
Link: http://lkml.kernel.org/r/20200426112950.1803-1-madhuparnabhowmik10@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 10af330153b5ec179abc473f43f84661b825b3fc..0b85a80ae7ef626f7265e2241f69512e93fa2f06 100644 (file)
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -2384,13 +2384,6 @@ static struct mport_dev *mport_cdev_add(struct rio_mport *mport)
        cdev_init(&md->cdev, &mport_fops);
        md->cdev.owner = THIS_MODULE;
 
-       ret = cdev_device_add(&md->cdev, &md->dev);
-       if (ret) {
-               rmcd_error("Failed to register mport %d (err=%d)",
-                      mport->id, ret);
-               goto err_cdev;
-       }
-
        INIT_LIST_HEAD(&md->doorbells);
        spin_lock_init(&md->db_lock);
        INIT_LIST_HEAD(&md->portwrites);
@@ -2410,6 +2403,13 @@ static struct mport_dev *mport_cdev_add(struct rio_mport *mport)
 #else
        md->properties.transfer_mode |= RIO_TRANSFER_MODE_TRANSFER;
 #endif
+
+       ret = cdev_device_add(&md->cdev, &md->dev);
+       if (ret) {
+               rmcd_error("Failed to register mport %d (err=%d)",
+                      mport->id, ret);
+               goto err_cdev;
+       }
        ret = rio_query_mport(mport, &attr);
        if (!ret) {
                md->properties.flags = attr.flags;