On Tue, Apr 25, 2017 at 04:55:26PM -0700, Adrian Salido wrote:
> The driver_override implementation is susceptible to race condition when
> different threads are reading vs storing a different driver override.
> Add locking to avoid race condition.
>
> Fixes: 3d713e0e382e ("driver core: platform: add device binding path
> 'driver_override'")
> Cc: sta...@vger.kernel.org
> Signed-off-by: Adrian Salido <sali...@google.com>
> ---
> drivers/base/platform.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index c2456839214a..493e03fa0e07 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -866,7 +866,7 @@ static ssize_t driver_override_store(struct device *dev,
> const char *buf, size_t count)
> {
> struct platform_device *pdev = to_platform_device(dev);
> - char *driver_override, *old = pdev->driver_override, *cp;
> + char *driver_override, *old, *cp;
>
> if (count > PATH_MAX)
> return -EINVAL;
> @@ -879,12 +879,15 @@ static ssize_t driver_override_store(struct device *dev,
> if (cp)
> *cp = '\0';
>
> + device_lock(dev);
> + old = pdev->driver_override;
> if (strlen(driver_override)) {
> pdev->driver_override = driver_override;
> } else {
> kfree(driver_override);
> pdev->driver_override = NULL;
> }
> + device_unlock(dev);
>
> kfree(old);
Shouldn't you move the lock until after the kfree()? Or am I missing
what the lock is trying to protect here?
>
> @@ -895,8 +898,12 @@ static ssize_t driver_override_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct platform_device *pdev = to_platform_device(dev);
> + ssize_t len;
>
> - return sprintf(buf, "%s\n", pdev->driver_override);
> + device_lock(dev);
> + len = sprintf(buf, "%s\n", pdev->driver_override);
> + device_unlock(dev);
> + return len;
Why does the show function need to be changed at all? How can anything
"race" here?
thanks,
greg k-h
