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 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>

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index f8c01fbef64d..4a3ac31c07d0 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;
 
         /* 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);