Messages in this thread | | | Subject | Re: [PATCH net] vhost: validate log when IOTLB is enabled | From | Jason Wang <> | Date | Fri, 30 Mar 2018 10:27:07 +0800 |
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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@syzkaller.appspotmail.com >> Signed-off-by: Jason Wang<jasowang@redhat.com> > 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
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