Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5FF7F22DC2
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Todd Kjos <tkjos@google.com>
Subject: [PATCH 4.4 36/44] ARM: amba: Fix race condition with driver_override
Date:   Mon, 30 Apr 2018 12:24:47 -0700
Message-Id: <20180430190947.776165866@linuxfoundation.org>
In-Reply-To: <20180430190946.093694747@linuxfoundation.org>
References: <20180430190946.093694747@linuxfoundation.org>
User-Agent: quilt/0.65
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Geert Uytterhoeven <geert+renesas@glider.be>

commit 6a7228d90d42bcacfe38786756ba62762b91c20a upstream.

The driver_override implementation is susceptible to a race condition
when different threads are reading vs storing a different driver
override.  Add locking to avoid this race condition.

Cfr. commits 6265539776a0810b ("driver core: platform: fix race
condition with driver_override") and 9561475db680f714 ("PCI: Fix race
condition with driver_override").

Fixes: 3cf385713460eb2b ("ARM: 8256/1: driver coamba: add device binding path 'driver_override'")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Todd Kjos <tkjos@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/amba/bus.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -68,8 +68,12 @@ static ssize_t driver_override_show(stru
 				    struct device_attribute *attr, char *buf)
 {
 	struct amba_device *dev = to_amba_device(_dev);
+	ssize_t len;
 
-	return sprintf(buf, "%s\n", dev->driver_override);
+	device_lock(_dev);
+	len = sprintf(buf, "%s\n", dev->driver_override);
+	device_unlock(_dev);
+	return len;
 }
 
 static ssize_t driver_override_store(struct device *_dev,
@@ -77,7 +81,7 @@ static ssize_t driver_override_store(str
 				     const char *buf, size_t count)
 {
 	struct amba_device *dev = to_amba_device(_dev);
-	char *driver_override, *old = dev->driver_override, *cp;
+	char *driver_override, *old, *cp;
 
 	if (count > PATH_MAX)
 		return -EINVAL;
@@ -90,12 +94,15 @@ static ssize_t driver_override_store(str
 	if (cp)
 		*cp = '\0';
 
+	device_lock(_dev);
+	old = dev->driver_override;
 	if (strlen(driver_override)) {
 		dev->driver_override = driver_override;
 	} else {
 	       kfree(driver_override);
 	       dev->driver_override = NULL;
 	}
+	device_unlock(_dev);
 
 	kfree(old);