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    Subject[PATCH 4.9 51/64] PCI: Fix race condition with driver_override
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Nicolai Stange <nstange@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 <nstange@suse.de>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@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);


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