linux-kernel - Re: [PATCH net V2 2/2] macvtap: signal truncated packets

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Date:	Tue, 10 Dec 2013 17:29:51 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [PATCH net V2 2/2] macvtap: signal truncated packets

On Tue, Dec 10, 2013 at 01:49:46PM +0800, Jason Wang wrote:
> macvtap_put_user() never return a value grater than iov length, this in fact
> bypasses the truncated checking in macvtap_recvmsg(). Fix this by always
> returning the size of packet plus the possible vlan header to let the trunca
> checking work.
> 
> Cc: Vlad Yasevich <vyasevich@...il.com>
> Cc: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> Changes from v1:
> - increase total unconditionally
> - do not move the structure veth out of the vlan handling block
> ---
>  drivers/net/macvtap.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 957cc5c..ded4b2c 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -770,7 +770,7 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
>  	int ret;
>  	int vnet_hdr_len = 0;
>  	int vlan_offset = 0;
> -	int copied;
> +	int copied, offset;
>  
>  	if (q->flags & IFF_VNET_HDR) {
>  		struct virtio_net_hdr vnet_hdr;
> @@ -785,7 +785,8 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
>  		if (memcpy_toiovecend(iv, (void *)&vnet_hdr, 0, sizeof(vnet_hdr)))
>  			return -EFAULT;
>  	}
> -	copied = vnet_hdr_len;
> +	offset = copied = vnet_hdr_len;
> +	copied += skb->len;
>  
>  	if (!vlan_tx_tag_present(skb))
>  		len = min_t(int, skb->len, len);
> @@ -800,24 +801,24 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
>  
>  		vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
>  		len = min_t(int, skb->len + VLAN_HLEN, len);
> +		copied += VLAN_HLEN;
>  
>  		copy = min_t(int, vlan_offset, len);
> -		ret = skb_copy_datagram_const_iovec(skb, 0, iv, copied, copy);
> +		ret = skb_copy_datagram_const_iovec(skb, 0, iv, offset, copy);
>  		len -= copy;
> -		copied += copy;
> +		offset += copy;
>  		if (ret || !len)
>  			goto done;
>  
>  		copy = min_t(int, sizeof(veth), len);
> -		ret = memcpy_toiovecend(iv, (void *)&veth, copied, copy);
> +		ret = memcpy_toiovecend(iv, (void *)&veth, offset, copy);
>  		len -= copy;
> -		copied += copy;
> +		offset += copy;
>  		if (ret || !len)
>  			goto done;
>  	}
>  
> -	ret = skb_copy_datagram_const_iovec(skb, vlan_offset, iv, copied, len);
> -	copied += len;
> +	ret = skb_copy_datagram_const_iovec(skb, vlan_offset, iv, offset, len);
>  
>  done:
>  	return ret ? ret : copied;

I commented on this already. copied is how much we copied,
so its value is correct.
You want to name the new one total_len or something along
these lines and return it.

> @@ -875,7 +876,7 @@ static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
>  	}
>  
>  	ret = macvtap_do_read(q, iocb, iv, len, file->f_flags & O_NONBLOCK);
> -	ret = min_t(ssize_t, ret, len); /* XXX copied from tun.c. Why? */
> +	ret = min_t(ssize_t, ret, len);
>  	if (ret > 0)
>  		iocb->ki_pos = ret;
>  out:
> -- 
> 1.8.3.2
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