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Date:   Fri, 9 Mar 2018 10:30:17 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Alexander Potapenko <glider@...gle.com>
Cc:     Dmitriy Vyukov <dvyukov@...gle.com>, kvm@...r.kernel.org,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH] vhost_net: initialize rx_ring in vhost_net_open()



On 2018年03月09日 00:00, Michael S. Tsirkin wrote:
> On Thu, Mar 08, 2018 at 04:55:39PM +0100, Alexander Potapenko wrote:
>> On Thu, Mar 8, 2018 at 4:33 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
>>> On Thu, Mar 08, 2018 at 02:37:17PM +0100, Alexander Potapenko wrote:
>>>> KMSAN reported a use of uninit memory in vhost_net_buf_unproduce()
>>>> while trying to access n->vqs[VHOST_NET_VQ_TX].rx_ring:
>>>>
>>>> ==================================================================
>>>> BUG: KMSAN: use of uninitialized memory in vhost_net_buf_unproduce+0x7bb/0x9a0 drivers/vho
>>>> et.c:170
>>>> CPU: 0 PID: 3021 Comm: syz-fuzzer Not tainted 4.16.0-rc4+ #3853
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>>>> Call Trace:
>>>>   __dump_stack lib/dump_stack.c:17 [inline]
>>>>   dump_stack+0x185/0x1d0 lib/dump_stack.c:53
>>>>   kmsan_report+0x142/0x1f0 mm/kmsan/kmsan.c:1093
>>>>   __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:676
>>>>   vhost_net_buf_unproduce+0x7bb/0x9a0 drivers/vhost/net.c:170
>>>>   vhost_net_stop_vq drivers/vhost/net.c:974 [inline]
>>>>   vhost_net_stop+0x146/0x380 drivers/vhost/net.c:982
>>>>   vhost_net_release+0xb1/0x4f0 drivers/vhost/net.c:1015
>>>>   __fput+0x49f/0xa00 fs/file_table.c:209
>>>>   ____fput+0x37/0x40 fs/file_table.c:243
>>>>   task_work_run+0x243/0x2c0 kernel/task_work.c:113
>>>>   tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>>>>   exit_to_usermode_loop arch/x86/entry/common.c:166 [inline]
>>>>   prepare_exit_to_usermode+0x349/0x3b0 arch/x86/entry/common.c:196
>>>>   syscall_return_slowpath+0xf3/0x6d0 arch/x86/entry/common.c:265
>>>>   do_syscall_64+0x34d/0x450 arch/x86/entry/common.c:292
>>>> ...
>>>> origin:
>>>>   kmsan_save_stack_with_flags mm/kmsan/kmsan.c:303 [inline]
>>>>   kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:213
>>>>   kmsan_kmalloc_large+0x6f/0xd0 mm/kmsan/kmsan.c:392
>>>>   kmalloc_large_node_hook mm/slub.c:1366 [inline]
>>>>   kmalloc_large_node mm/slub.c:3808 [inline]
>>>>   __kmalloc_node+0x100e/0x1290 mm/slub.c:3818
>>>>   kmalloc_node include/linux/slab.h:554 [inline]
>>>>   kvmalloc_node+0x1a5/0x2e0 mm/util.c:419
>>>>   kvmalloc include/linux/mm.h:541 [inline]
>>>>   vhost_net_open+0x64/0x5f0 drivers/vhost/net.c:921
>>>>   misc_open+0x7b5/0x8b0 drivers/char/misc.c:154
>>>>   chrdev_open+0xc28/0xd90 fs/char_dev.c:417
>>>>   do_dentry_open+0xccb/0x1430 fs/open.c:752
>>>>   vfs_open+0x272/0x2e0 fs/open.c:866
>>>>   do_last fs/namei.c:3378 [inline]
>>>>   path_openat+0x49ad/0x6580 fs/namei.c:3519
>>>>   do_filp_open+0x267/0x640 fs/namei.c:3553
>>>>   do_sys_open+0x6ad/0x9c0 fs/open.c:1059
>>>>   SYSC_openat+0xc7/0xe0 fs/open.c:1086
>>>>   SyS_openat+0x63/0x90 fs/open.c:1080
>>>>   do_syscall_64+0x2f1/0x450 arch/x86/entry/common.c:287
>>>> ==================================================================
>>>>
>>>> Signed-off-by: Alexander Potapenko <glider@...gle.com>
>>>> ---
>>>>   drivers/vhost/net.c | 1 +
>>>>   1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>>>> index 610cba276d47..60f1080bffc7 100644
>>>> --- a/drivers/vhost/net.c
>>>> +++ b/drivers/vhost/net.c
>>>> @@ -948,6 +948,7 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>>>>                n->vqs[i].done_idx = 0;
>>>>                n->vqs[i].vhost_hlen = 0;
>>>>                n->vqs[i].sock_hlen = 0;
>>>> +             n->vqs[i].rx_ring = NULL;
>>>>                vhost_net_buf_init(&n->vqs[i].rxq);
>>>>        }
>>>>        vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
>>>> --
>>>> 2.16.2.395.g2e18187dfd-goog
>>>
>>> I suspect that's not sufficient. rx ring is tied to the tap device.
>>> I think we need to drop it every time we drop the device.
>> Unfortunately I've no idea where is the device dropped. Are you
>> referring to vhost_net_vq_reset()?
>> I can fix that part if needed, but won't be able to validate it with KMSAN.
> I see several issues. For example in vhost_net_set_backend
> if there's a value then rx ring will point to the
> ring of the wrong socket.
> Something like the below might help but we really need
> documentation of when is rx_ring valid. Is it only valid
> when private-data is valid?

I think so, we need keep rx_ring synced with private_data.

> If yes need to make sure
> we reset it with private_data.
>
> Also I see __skb_array_destroy_skb used with ptr_ring which
> seems suspicious: how do we know the entries are skbs?

Good catch, will post an independent patch to fix this.

>
> Patch below is on top of yours, and
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>
> But I really would like Jason to look and come up with a
> patch to address all these issues.
>
> ---
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 610cba2..7a65b69 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -972,6 +973,7 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
>   	vhost_net_disable_vq(n, vq);
>   	vq->private_data = NULL;
>   	vhost_net_buf_unproduce(nvq);
> +	vq->rx_ring = NULL;
>   	mutex_unlock(&vq->mutex);
>   	return sock;
>   }
> @@ -1161,8 +1163,6 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
>   		vhost_net_disable_vq(n, vq);
>   		vq->private_data = sock;
>   		vhost_net_buf_unproduce(nvq);
> -		if (index == VHOST_NET_VQ_RX)
> -			nvq->rx_ring = get_tap_ptr_ring(fd);
>   		r = vhost_vq_init_access(vq);
>   		if (r)
>   			goto err_used;
> @@ -1172,6 +1172,10 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
>   
>   		oldubufs = nvq->ubufs;
>   		nvq->ubufs = ubufs;
> +		if (index == VHOST_NET_VQ_RX)
> +			nvq->rx_ring = get_tap_ptr_ring(fd);
> +		else
> +			nvq->rx_ring = NULL;
>   

Any reason to move those after vhost_net_enable_vq()? And consider we 
won't try to assign rx_ring to TX, the "else" part seems unnecessary.

Thanks

>   		n->tx_packets = 0;
>   		n->tx_zcopy_err = 0;

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