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From:   Geert Uytterhoeven <geert+renesas@glider.be>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Russell King <linux@armlinux.org.uk>,
        Adrian Salido <salidoa@google.com>,
        Nicolai Stange <nstange@suse.de>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        Todd Kjos <tkjos@android.com>, linux-kernel@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>
Subject: [PATCH v2 2/4] ARM: amba: Fix race condition with driver_override
Date:   Tue, 10 Apr 2018 15:21:44 +0200
Message-Id: <1523366506-19832-3-git-send-email-geert+renesas@glider.be>
In-Reply-To: <1523366506-19832-1-git-send-email-geert+renesas@glider.be>
References: <1523366506-19832-1-git-send-email-geert+renesas@glider.be>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 6ffd778352e6d953..36c5653ced5742b7 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -69,8 +69,12 @@ static ssize_t driver_override_show(struct device *_dev,
 				    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,
@@ -78,7 +82,7 @@ static ssize_t driver_override_store(struct device *_dev,
 				     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;
@@ -91,12 +95,15 @@ static ssize_t driver_override_store(struct device *_dev,
 	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);
 
-- 
2.7.4