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    Subject[PATCH 4.14 133/166] rapidio: avoid data race between file operation callbacks and mport_cdev_add().
    Date
    From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

    [ Upstream commit e1c3cdb26ab881b77486dc50370356a349077c74 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 f15f6d1e1070a..f207f8725993c 100644
    --- a/drivers/rapidio/devices/rio_mport_cdev.c
    +++ b/drivers/rapidio/devices/rio_mport_cdev.c
    @@ -2464,13 +2464,6 @@ 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);
    @@ -2490,6 +2483,13 @@ 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;
    --
    2.25.1


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