On Tue, Feb 23, 2010 at 07:32:58PM +0200, Michael S. Tsirkin wrote:
> On Tue, Feb 23, 2010 at 07:34:34PM +0200, Gleb Natapov wrote:
> > On Tue, Feb 23, 2010 at 06:57:58PM +0200, Michael S. Tsirkin wrote:
> > > get_user_pages_fast returns number of pages on success, negative value
> > > on failure, but never 0. Fix vhost code to match this logic.
> > >
> > > Signed-off-by: Michael S. Tsirkin <[email protected]>
> > > ---
> > > drivers/vhost/vhost.c | 3 ++-
> > > 1 files changed, 2 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index d4f8fdf..d003504 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -646,8 +646,9 @@ static int set_bit_to_user(int nr, void __user *addr)
> > > int bit = nr + (log % PAGE_SIZE) * 8;
> > > int r;
> > > r = get_user_pages_fast(log, 1, 1, &page);
> > > - if (r)
> > > + if (r < 0)
> > > return r;
> > > + BUG_ON(r != 1);
> > Can't this be easily triggered from user space?
>
> I think no. get_user_pages_fast always returns number of pages
> pinned (in this case always 1) or an error (< 0).
> Anything else is a kernel bug.
>
But what if page is unmapped from userspace?
> > > base = kmap_atomic(page, KM_USER0);
> > > set_bit(bit, base);
> > > kunmap_atomic(base, KM_USER0);
> > > --
> > > 1.7.0.18.g0d53a5
> >
> > --
> > Gleb.
--
Gleb.
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