[PATCH AUTOSEL 4.4 16/64] ACPI: EC: Reference count query handlers under lock

Sasha Levin
2020-09-18T02:23:05Z

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 43f20328f830e..3096c087b7328 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -943,29 +943,21 @@ void acpi_ec_unblock_transactions_early(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