Driver core: fix race in dev_driver_string

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@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 353b13782165..f1290cbd1350 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -56,7 +56,14 @@ static inline int device_is_not_partition(struct device *dev)
  */
 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 : ""));
 }