On 12/6/19 1:09 PM, Nuernberger, Stefan wrote:
On Fri, 2019-12-06 at 10:11 -0500, Boris Ostrovsky wrote:
On 12/6/19 8:48 AM, Stefan Nuernberger wrote:
From: Uwe Dannowski uwed@amazon.de
Reading /sys/bus/pci/drivers/pciback/quirks while unbinding can result in dereferencing a NULL pointer. Instead, skip printing information about the dangling quirk.
Reported-by: Conny Seidel consei@amazon.de Signed-off-by: Uwe Dannowski uwed@amazon.de Signed-off-by: Stefan Nuernberger snu@amazon.com
Cc: xen-devel@lists.xenproject.org Cc: stable@vger.kernel.org
drivers/xen/xen-pciback/pci_stub.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen- pciback/pci_stub.c index 097410a7cdb7..da725e474294 100644 --- a/drivers/xen/xen-pciback/pci_stub.c +++ b/drivers/xen/xen-pciback/pci_stub.c @@ -1346,6 +1346,8 @@ static ssize_t quirks_show(struct device_driver *drv, char *buf) quirk->devid.subdevice); dev_data = pci_get_drvdata(quirk->pdev);
if (!dev_data)continue;list_for_each_entry(cfg_entry, &dev_data-
config_fields, list) {
Couldn't you have the same race here?
Not quite the same, but it might not be entirely safe yet. The 'quirks_show' takes the 'device_ids_lock' and races with unbind / 'pcistub_device_release' "which takes device_lock mutex". So this might now be a UAF read access instead of a NULL pointer dereference.
Yes, that's what I meant (although I don't see much difference in this context).
We have not observed adversarial effects in our testing (compared to the obvious issues with NULL pointer) but that's not a guarantee of course.
So should quirks_show actually be protected by pcistub_devices_lock instead as are other functions that access dev_data? Does it need both locks in that case?
device_ids_lock protects device_ids list, which is not what you are trying to access, so that doesn't look like right lock to hold. And AFAICT pcistub_devices_lock is not held when device data is cleared in pcistub_device_release() (which I think is where we are racing).
-boris