ARM: amba: Fix race condition with driver_override

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 cddafb61a131d353 ("driver core: platform: fix race
condition with driver_override") and 7551b6075e6586ae ("PCI: Fix race
condition with driver_override").

Fixes: 1a90ac7b8df327bc ("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>

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index f8c01fbef64d6e7bd341073f2dccc4d0de15b764..4a3ac31c07d0ee49615a00af001e49ff8e30f005 100644 (file)
--- 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;
 
        /* We need to keep extra room for a newline */
        if (count >= (PAGE_SIZE - 1))
@@ -92,12 +96,15 @@ 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);