Re: patch "ARM: amba: Fix race condition with driver_override" added to char-misc-linus

Hi Greg,

On Wed, Apr 25, 2018 at 6:07 PM, gregkh@linuxfoundation.org wrote:

This is a note to let you know that I've just added the patch titled

ARM: amba: Fix race condition with driver_override

to my char-misc git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git in the char-misc-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

Doh, I hadn't noticed you modified my patch, and introduced a bug...

From 6b614a87f3f477571e319281e84dba11e0ea0a76 Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven geert+renesas@glider.be Date: Tue, 10 Apr 2018 15:21:44 +0200 Subject: 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

---

drivers/amba/bus.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c index 594c228d2f02..c77eb6e65646 100644 --- a/drivers/amba/bus.c +++ b/drivers/amba/bus.c @@ -69,11 +69,15 @@ 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;
  
    if (!dev->driver_override)
            return 0;
  

With the above still present, it should be covered by the lock below, too. Else the output is still subject to the race condition.

•   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, @@ -81,7 +85,7 @@ 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;
  
    if (count > PATH_MAX)
            return -EINVAL;
  

@@ -94,12 +98,15 @@ 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);
  
  

-- 2.17.0