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

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Message-ID: <CACT4Y+bzWiPvV+pVvys4v8CwUhF7iYVskxn_yeo6ztN5uKA0VA@mail.gmail.com>
Date:   Fri, 27 Apr 2018 18:25:19 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Kevin Easton <kevin@...rana.org>, Jason Wang <jasowang@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH net] vhost: Use kzalloc() to allocate vhost_msg_node

On Fri, Apr 27, 2018 at 6:15 PM, Michael S. Tsirkin <mst@...hat.com> 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
>> >
>> > Does it help if a patch naming the padding is applied,
>> > and then we init just the relevant field?
>> > Just curious.
>>
>> Yes, it would help.
>
> I think it's slightly better that way then. node has a lot of internal
> stuff we don't care to init. Would you mind taking my patch and building
> on top of that then?


But it's asking for more information leaks in future. This looks like
work for compiler.


>> >> ---
>> >>  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;
>> >> --
>> >> 2.8.1