[098/127] rapidio: avoid data race between file operation callbacks and mport_cdev_add().

Commit Message

Andrew Morton June 4, 2020, 11:51 p.m. UTC

From: Madhuparna Bhowmik <[e-mail]>
Subject: 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).

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Madhuparna Bhowmik <[e-mail]>
Acked-by: Alexandre Bounine <[e-mail]>
Cc: Matt Porter <[e-mail]>
Cc: Dan Carpenter <[e-mail]>
Cc: Mike Marshall <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Cc: Allison Randal <[e-mail]>
Cc: Pavel Andrianov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 drivers/rapidio/devices/rio_mport_cdev.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

Patch

--- a/drivers/rapidio/devices/rio_mport_cdev.c~rapidio-avoid-data-race-between-file-operation-callbacks-and-mport_cdev_add
+++ a/drivers/rapidio/devices/rio_mport_cdev.c
@@ -2384,13 +2384,6 @@  static struct mport_dev *mport_cdev_add(
 	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(
 #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;