On 2018年03月29日 22:44, Michael S. Tsirkin wrote:
On Thu, Mar 29, 2018 at 04:00:04PM +0800, Jason Wang wrote:Vq log_base is the userspace address of bitmap which has nothing to do with IOTLB. So it needs to be validated unconditionally otherwise we may try use 0 as log_base which may lead to pin pages that will lead unexpected result (e.g trigger BUG_ON() in set_bit_to_user()). Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API") Reported-by:syzbot+6304bf97ef436580fede@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Jason Wang<jasowang@xxxxxxxxxx>One follow-up question: We still observe that get user pages returns 0 sometimes. While I agree we should not pass in unvalidated addresses, isn't this worth documenting?
Looking at get_user_pages_fast(), it has: if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, (void __user *)start, len))) return 0; So this is expected I think. Thanks
