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    Subject[PATCH AUTOSEL 4.9 22/90] ACPI: EC: Reference count query handlers under lock
    Date
    From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

    [ Upstream commit 3df663a147fe077a6ee8444ec626738946e65547 ]

    There is a race condition in acpi_ec_get_query_handler()
    theoretically allowing query handlers to go away before refernce
    counting them.

    In order to avoid it, call kref_get() on query handlers under
    ec->mutex.

    Also simplify the code a bit while at it.

    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/acpi/ec.c | 16 ++++------------
    1 file changed, 4 insertions(+), 12 deletions(-)

    diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
    index 307b3e28f34ce..8781b5dc97f1c 100644
    --- a/drivers/acpi/ec.c
    +++ b/drivers/acpi/ec.c
    @@ -1049,29 +1049,21 @@ void acpi_ec_unblock_transactions(void)
    /* --------------------------------------------------------------------------
    Event Management
    -------------------------------------------------------------------------- */
    -static struct acpi_ec_query_handler *
    -acpi_ec_get_query_handler(struct acpi_ec_query_handler *handler)
    -{
    - if (handler)
    - kref_get(&handler->kref);
    - return handler;
    -}
    -
    static struct acpi_ec_query_handler *
    acpi_ec_get_query_handler_by_value(struct acpi_ec *ec, u8 value)
    {
    struct acpi_ec_query_handler *handler;
    - bool found = false;

    mutex_lock(&ec->mutex);
    list_for_each_entry(handler, &ec->list, node) {
    if (value == handler->query_bit) {
    - found = true;
    - break;
    + kref_get(&handler->kref);
    + mutex_unlock(&ec->mutex);
    + return handler;
    }
    }
    mutex_unlock(&ec->mutex);
    - return found ? acpi_ec_get_query_handler(handler) : NULL;
    + return NULL;
    }

    static void acpi_ec_query_handler_release(struct kref *kref)
    --
    2.25.1
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