linux-kernel - [062/151] Driver core: fix race in dev_driver

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Date:	Wed, 16 Dec 2009 19:55:59 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.org>
Subject: [062/151] Driver core: fix race in dev_driver_string

2.6.32-stable review patch.  If anyone has any objections, please let us know.

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

From: Alan Stern <stern@...land.harvard.edu>

commit 3589972e51fac1e02d0aaa576fa47f568cb94d40 upstream.

This patch (as1310) works around a race in dev_driver_string().  If
the device is unbound while the function is running, dev->driver might
become NULL after we test it and before we dereference it.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>
Cc: Oliver Neukum <oliver@...kum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/base/core.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -56,7 +56,14 @@ static inline int device_is_not_partitio
  */
 const char *dev_driver_string(const struct device *dev)
 {
-	return dev->driver ? dev->driver->name :
+	struct device_driver *drv;
+
+	/* dev->driver can change to NULL underneath us because of unbinding,
+	 * so be careful about accessing it.  dev->bus and dev->class should
+	 * never change once they are set, so they don't need special care.
+	 */
+	drv = ACCESS_ONCE(dev->driver);
+	return drv ? drv->name :
 			(dev->bus ? dev->bus->name :
 			(dev->class ? dev->class->name : ""));
 }


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