The patch 7032269e87a "HID: hiddev: protect against
disconnect/NULL-dereference race" added a check to make sure that "hid"
was non-NULL. The problem is that it added the check after "hid" had
already been dereferenced.
drivers/hid/usbhid/hiddev.c +606 hiddev_ioctl(19)
warn: variable dereferenced before check 'hid'
599 struct usbhid_device *usbhid = hid->driver_data;
^^^^^^^^^^^^^^^^
dereferenced here.
600 void __user *user_arg = (void __user *)arg;
601 int i, r;
602
603 /* Called without BKL by compat methods so no BKL taken */
604
605 /* FIXME: Who or what stop this racing with a disconnect ?? */
606 if (!hiddev->exist || !hid)
^^^^
new check added here.
607 return -EIO;
So obviously in hind-sight this patch didn't fix the user's problem.
Also the user reported a NULL dereference, yes, but the stack dump which
says: "BUG: unable to handle kernel paging request at 6b6b6b6b" is a use
after free bug and that isn't addressed by adding a check for NULL.
I am just looking at this because it showed up with my static checker
and I'm not very familiar with this code. I think we need to take
"hiddev->existancelock" and make sure that exist is true before we
dereference hiddev in the ioctl function? Also it seems like there
should probably be some locking in hiddev_release().
regards,
dan carpenter
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