PCI: 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 the race condition.

This is in close analogy to commit 6265539776a0 ("driver core: platform:
fix race condition with driver_override") from Adrian Salido.

Fixes: 782a985d7af2 ("PCI: Introduce new device binding path using pci_dev.driver_override")
Signed-off-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org	# v3.16+

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 1eecfa301f7f..8e075ea2743e 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -686,7 +686,7 @@ static ssize_t driver_override_store(struct device *dev,
                                      const char *buf, size_t count)
 {
         struct pci_dev *pdev = to_pci_dev(dev);
-        char *driver_override, *old = pdev->driver_override, *cp;
+        char *driver_override, *old, *cp;
 
         /* We need to keep extra room for a newline */
         if (count >= (PAGE_SIZE - 1))
@@ -700,12 +700,15 @@ 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);
 
@@ -716,8 +719,12 @@ static ssize_t driver_override_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
 {
         struct pci_dev *pdev = to_pci_dev(dev);
+        ssize_t len;
 
-        return snprintf(buf, PAGE_SIZE, "%s\n", pdev->driver_override);
+        device_lock(dev);
+        len = snprintf(buf, PAGE_SIZE, "%s\n", pdev->driver_override);
+        device_unlock(dev);
+        return len;
 }
 static DEVICE_ATTR_RW(driver_override);