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    Subject[PATCH 5.4 137/168] staging: comedi: Fix comedi_device refcnt leak in comedi_open
    Date
    From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

    commit 332e0e17ad49e084b7db670ef43b5eb59abd9e34 upstream.

    comedi_open() invokes comedi_dev_get_from_minor(), which returns a
    reference of the COMEDI device to "dev" with increased refcount.

    When comedi_open() returns, "dev" becomes invalid, so the refcount
    should be decreased to keep refcount balanced.

    The reference counting issue happens in one exception handling path of
    comedi_open(). When "cfp" allocation is failed, the refcnt increased by
    comedi_dev_get_from_minor() is not decreased, causing a refcnt leak.

    Fix this issue by calling comedi_dev_put() on this error path when "cfp"
    allocation is failed.

    Fixes: 20f083c07565 ("staging: comedi: prepare support for per-file read and write subdevices")
    Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
    Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
    Link: https://lore.kernel.org/r/1587361459-83622-1-git-send-email-xiyuyang19@fudan.edu.cn
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/staging/comedi/comedi_fops.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/drivers/staging/comedi/comedi_fops.c
    +++ b/drivers/staging/comedi/comedi_fops.c
    @@ -2725,8 +2725,10 @@ static int comedi_open(struct inode *ino
    }

    cfp = kzalloc(sizeof(*cfp), GFP_KERNEL);
    - if (!cfp)
    + if (!cfp) {
    + comedi_dev_put(dev);
    return -ENOMEM;
    + }

    cfp->dev = dev;


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