linux-kernel - [PATCH] ACPI: EC: Reference count query handlers under lock

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Date:   Thu, 19 Dec 2019 23:50:12 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux ACPI <linux-acpi@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] ACPI: EC: Reference count query handlers under lock

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

There is a race condition in acpi_ec_get_query_handler()
theoretically allowing query handlers to go away before
reference 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@...el.com>
---
 drivers/acpi/ec.c |   16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

Index: linux-pm/drivers/acpi/ec.c
===================================================================
--- linux-pm.orig/drivers/acpi/ec.c
+++ linux-pm/drivers/acpi/ec.c
@@ -1053,28 +1053,20 @@ 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)