[PATCH 4.9 51/64] PCI: Fix race condition with driver_override

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolai Stange <nsta...@suse.de>

commit 9561475db680f7144d2223a409dd3d7e322aca03 upstream.

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 <nsta...@suse.de>
Signed-off-by: Bjorn Helgaas <bhelg...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -527,7 +527,7 @@ static ssize_t driver_override_store(str
                                     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))
@@ -541,12 +541,15 @@ static ssize_t driver_override_store(str
        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);
 
@@ -557,8 +560,12 @@ static ssize_t driver_override_show(stru
                                    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);