From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH 3/3] vhost: fix get_user_pages_fast error handling Date: Tue, 23 Feb 2010 19:39:52 +0200 Message-ID: <20100223173952.GC9834@redhat.com> References: <82ba8c97ce55dd4bf9972ad755961cd14e6a0938.1266943453.git.mst@redhat.com> <20100223173434.GB9834@redhat.com> <20100223173258.GA25338@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Rusty Russell , kvm@vger.kernel.org, virtualization@lists.osdl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, David Miller , markmc@redhat.com, herbert.xu@redhat.com, quintela@redhat.com, dlaor@redhat.com, avi@redhat.com To: "Michael S. Tsirkin" Return-path: Content-Disposition: inline In-Reply-To: <20100223173258.GA25338@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 > > > --- > > > 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.