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    Subject[PATCH 5.4 028/134] kobject: Make sure the parent does not get released before its children
    Date
    From: Heikki Krogerus <heikki.krogerus@linux.intel.com>

    [ Upstream commit 4ef12f7198023c09ad6d25b652bd8748c965c7fa ]

    In the function kobject_cleanup(), kobject_del(kobj) is
    called before the kobj->release(). That makes it possible to
    release the parent of the kobject before the kobject itself.

    To fix that, adding function __kboject_del() that does
    everything that kobject_del() does except release the parent
    reference. kobject_cleanup() then calls __kobject_del()
    instead of kobject_del(), and separately decrements the
    reference count of the parent kobject after kobj->release()
    has been called.

    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Reported-by: kernel test robot <rong.a.chen@intel.com>
    Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
    Suggested-by: "Rafael J. Wysocki" <rafael@kernel.org>
    Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
    Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
    Tested-by: Brendan Higgins <brendanhiggins@google.com>
    Acked-by: Randy Dunlap <rdunlap@infradead.org>
    Link: https://lore.kernel.org/r/20200513151840.36400-1-heikki.krogerus@linux.intel.com
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    lib/kobject.c | 30 ++++++++++++++++++++----------
    1 file changed, 20 insertions(+), 10 deletions(-)

    diff --git a/lib/kobject.c b/lib/kobject.c
    index 83198cb37d8d..2bd631460e18 100644
    --- a/lib/kobject.c
    +++ b/lib/kobject.c
    @@ -599,14 +599,7 @@ int kobject_move(struct kobject *kobj, struct kobject *new_parent)
    }
    EXPORT_SYMBOL_GPL(kobject_move);

    -/**
    - * kobject_del() - Unlink kobject from hierarchy.
    - * @kobj: object.
    - *
    - * This is the function that should be called to delete an object
    - * successfully added via kobject_add().
    - */
    -void kobject_del(struct kobject *kobj)
    +static void __kobject_del(struct kobject *kobj)
    {
    struct kernfs_node *sd;
    const struct kobj_type *ktype;
    @@ -625,9 +618,23 @@ void kobject_del(struct kobject *kobj)

    kobj->state_in_sysfs = 0;
    kobj_kset_leave(kobj);
    - kobject_put(kobj->parent);
    kobj->parent = NULL;
    }
    +
    +/**
    + * kobject_del() - Unlink kobject from hierarchy.
    + * @kobj: object.
    + *
    + * This is the function that should be called to delete an object
    + * successfully added via kobject_add().
    + */
    +void kobject_del(struct kobject *kobj)
    +{
    + struct kobject *parent = kobj->parent;
    +
    + __kobject_del(kobj);
    + kobject_put(parent);
    +}
    EXPORT_SYMBOL(kobject_del);

    /**
    @@ -663,6 +670,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
    */
    static void kobject_cleanup(struct kobject *kobj)
    {
    + struct kobject *parent = kobj->parent;
    struct kobj_type *t = get_ktype(kobj);
    const char *name = kobj->name;

    @@ -684,7 +692,7 @@ static void kobject_cleanup(struct kobject *kobj)
    if (kobj->state_in_sysfs) {
    pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
    kobject_name(kobj), kobj);
    - kobject_del(kobj);
    + __kobject_del(kobj);
    }

    if (t && t->release) {
    @@ -698,6 +706,8 @@ static void kobject_cleanup(struct kobject *kobj)
    pr_debug("kobject: '%s': free name\n", name);
    kfree_const(name);
    }
    +
    + kobject_put(parent);
    }

    #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
    --
    2.25.1


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