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    Subject[PATCH 4.14 035/183] auxdisplay: ht16k33: fix potential user-after-free on module unload
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 69ef9bc54715fb1cb7786ada15774e469e822209 ]

    On module unload/remove, we need to ensure that work does not run
    after we have freed resources. Concretely, cancel_delayed_work()
    may return while the callback function is still running.

    >From kernel/workqueue.c:

    The work callback function may still be running on return,
    unless it returns true and the work doesn't re-arm itself.
    Explicitly flush or use cancel_delayed_work_sync() to wait on it.

    Link: https://lore.kernel.org/lkml/20190204220952.30761-1-TheSven73@googlemail.com/
    Reported-by: Sven Van Asbroeck <thesven73@gmail.com>
    Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
    Reviewed-by: Sven Van Asbroeck <TheSven73@gmail.com>
    Acked-by: Robin van der Gracht <robin@protonic.nl>
    Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/auxdisplay/ht16k33.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/auxdisplay/ht16k33.c b/drivers/auxdisplay/ht16k33.c
    index fbfa5b4cc567..a93ded300740 100644
    --- a/drivers/auxdisplay/ht16k33.c
    +++ b/drivers/auxdisplay/ht16k33.c
    @@ -517,7 +517,7 @@ static int ht16k33_remove(struct i2c_client *client)
    struct ht16k33_priv *priv = i2c_get_clientdata(client);
    struct ht16k33_fbdev *fbdev = &priv->fbdev;

    - cancel_delayed_work(&fbdev->work);
    + cancel_delayed_work_sync(&fbdev->work);
    unregister_framebuffer(fbdev->info);
    framebuffer_release(fbdev->info);
    free_page((unsigned long) fbdev->buffer);
    --
    2.19.1


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