linux-kernel - Re: [PATCH net] vhost: Use kzalloc() to allocate vhost_msg

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Message-ID: <20180508082716.GA21344@la.guarana.org>
Date:   Tue, 8 May 2018 04:27:16 -0400
From:   Kevin Easton <kevin@...rana.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net] vhost: Use kzalloc() to allocate vhost_msg_node

On Mon, May 07, 2018 at 04:03:25PM +0300, Michael S. Tsirkin wrote:
> On Fri, Apr 27, 2018 at 11:45:02AM -0400, Kevin Easton wrote:
> > The struct vhost_msg within struct vhost_msg_node is copied to userspace,
> > so it should be allocated with kzalloc() to ensure all structure padding
> > is zeroed.
> > 
> > Signed-off-by: Kevin Easton <kevin@...rana.org>
> > Reported-by: syzbot+87cfa083e727a224754b@...kaller.appspotmail.com
> > ---
> >  drivers/vhost/vhost.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index f3bd8e9..1b84dcff 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2339,7 +2339,7 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
> >  /* Create a new message. */
> >  struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
> >  {
> > -	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
> > +	struct vhost_msg_node *node = kzalloc(sizeof *node, GFP_KERNEL);
> >  	if (!node)
> >  		return NULL;
> >  	node->vq = vq;
> 
> 
> Let's just init the msg though.
> 
> OK it seems this is the best we can do for now,
> we need a new feature bit to fix it for 32 bit
> userspace on 64 bit kernels.
> 
> Does the following help?

Yes, the reproducer doesn't trigger the error with that patch applied.

    - Kevin