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From: Al Viro <viro@ZenIV.linux.org.uk>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: syzbot <syzbot+87cfa083e727a224754b@syzkaller.appspotmail.com>,
	avagin@openvz.org, davem@davemloft.net, dingtianhong@huawei.com,
	edumazet@google.com, elena.reshetova@intel.com,
	jasowang@redhat.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, matthew@mjdsystems.ca,
	mingo@kernel.org, netdev@vger.kernel.org, pabeni@redhat.com,
	syzkaller-bugs@googlegroups.com,
	virtualization@lists.linux-foundation.org, willemb@google.com
Subject: Re: KMSAN: uninit-value in _copy_to_iter (2)
Date: Thu, 7 Jun 2018 19:04:49 +0100	[thread overview]
Message-ID: <20180607180449.GS30522@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20180607205611-mutt-send-email-mst@kernel.org>

On Thu, Jun 07, 2018 at 08:59:06PM +0300, Michael S. Tsirkin wrote:
> On Thu, Jun 07, 2018 at 06:43:55PM +0100, Al Viro wrote:
> > On Thu, Jun 07, 2018 at 06:38:48PM +0300, Michael S. Tsirkin wrote:
> > > #syz test: https://github.com/google/kmsan.git/master d2d741e5d1898dfde1a75ea3d29a9a3e2edf0617
> > > 
> > > Subject: vhost: fix info leak
> > > 
> > > Fixes: CVE-2018-1118
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index f0be5f35ab28..9beefa6ed1ce 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -2345,6 +2345,9 @@ struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
> > >  	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
> > >  	if (!node)
> > >  		return NULL;
> > > +
> > > +	/* Make sure all padding within the structure is initialized. */
> > > +	memset(&node->msg, 0, sizeof node->msg);
> > 
> > Umm...  Maybe kzalloc(), then?  You have
> > 
> > struct vhost_msg_node {
> >   struct vhost_msg msg;
> >   struct vhost_virtqueue *vq;
> >   struct list_head node;
> > };
> > 
> > and that's what, 68 bytes in msg, then either 4 bytes pointer or
> > 4 bytes padding + 8 bytes pointer, then two pointers?  How much
> > does explicit partial memset() save you here?
> 
> Yes but 0 isn't a nop here so if this struct is used without
> a sensible initialization, it will crash elsewhere.
> I prefer KASAN to catch such uses.
> 
> 
> > >  	node->vq = vq;
> > >  	node->msg.type = type;

IDGI - what would your variant catch that kzalloc + 2 assignments won't?
Accesses to uninitialized ->node?  Because that's the only difference in
what is and is not initialized between those variants...

  reply	other threads:[~2018-06-07 18:05 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-23 16:56 syzbot
2018-04-25 19:19 ` syzbot
2018-06-07 15:38   ` Michael S. Tsirkin
2018-06-07 15:38     ` syzbot
2018-06-07 16:25     ` Dmitry Vyukov
2018-06-07 17:04       ` syzbot
2018-06-07 17:43     ` Al Viro
2018-06-07 17:59       ` Michael S. Tsirkin
2018-06-07 18:04         ` Al Viro [this message]
2018-06-07 19:29           ` Michael S. Tsirkin
2018-06-07 17:10   ` Michael S. Tsirkin
2018-06-07 17:31     ` syzbot
2018-04-27 15:45 ` [PATCH net] vhost: Use kzalloc() to allocate vhost_msg_node Kevin Easton
2018-04-27 16:05   ` Michael S. Tsirkin
2018-04-27 16:11     ` Dmitry Vyukov
2018-04-27 16:15       ` Michael S. Tsirkin
2018-04-27 16:25         ` Dmitry Vyukov
2018-04-27 16:29           ` Dmitry Vyukov
2018-04-27 19:36       ` Michael S. Tsirkin
2018-04-29  8:10         ` Dmitry Vyukov
2018-04-28  1:07     ` Kevin Easton
2018-04-28  1:51       ` Kevin Easton
2018-04-28  2:23         ` Jason Wang
2018-05-07 13:03   ` Michael S. Tsirkin
2018-05-07 13:12     ` Dmitry Vyukov
2018-05-08  8:27     ` Kevin Easton
2018-05-29 22:19   ` [net] " Guenter Roeck
2018-05-30  3:01     ` Michael S. Tsirkin
2018-05-30  3:42       ` Guenter Roeck
2018-06-04 12:34       ` Dmitry Vyukov

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