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Subject[PATCH] rapidio: Avoid data race between file operation callbacks and mport_cdev_add().
Date
From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

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

diff --git a/drivers/rapidio/devices/rio_mport_cdev.c b/drivers/rapidio/devices/rio_mport_cdev.c
index 8155f59ece38..40296378e5ee 100644
--- a/drivers/rapidio/devices/rio_mport_cdev.c
+++ b/drivers/rapidio/devices/rio_mport_cdev.c
@@ -2379,13 +2379,6 @@ 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);
@@ -2405,6 +2398,13 @@ 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;
--
2.17.1
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