Subject: Re: [PATCH 2/2] net/packet: send and receive pkt with given vnet_hdr_sz

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 9 Feb 2023 08:07:09 -0500

On Thu, Feb 09, 2023 at 08:43:15PM +0800, 沈安琪(凛玥) wrote:
> From: "Jianfeng Tan" <[email-masked]>
> 
> When raw socket is used as the backend for kernel vhost, currently it
> will regard the virtio net header as 10-byte, which is not always the
> case since some virtio features need virtio net header other than
> 10-byte, such as mrg_rxbuf and VERSION_1 that both need 12-byte virtio
> net header.
> 
> Instead of hardcoding virtio net header length to 10 bytes, tpacket_snd,
> tpacket_rcv, packet_snd and packet_recvmsg now get the virtio net header
> size that is recorded in packet_sock to indicate the exact virtio net
> header size that virtio user actually prepares in the packets. By doing
> so, it can fix the issue of incorrect mac header parsing when these
> virtio features that need virtio net header other than 10-byte are
> enable.
> 
> Signed-off-by: Jianfeng Tan <[email-masked]>
> Co-developed-by: Anqi Shen <[email-masked]>
> Signed-off-by: Anqi Shen <[email-masked]>

Does it handle VERSION_1 though? That one is also LE.
Would it be better to pass a features bitmap instead?

> ---
>  net/packet/af_packet.c | 48 +++++++++++++++++++++++++++++++++---------------
>  1 file changed, 33 insertions(+), 15 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index ab37baf..4f49939 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2092,18 +2092,25 @@ static unsigned int run_filter(struct sk_buff *skb,
>  }
>  
>  static int packet_rcv_vnet(struct msghdr *msg, const struct sk_buff *skb,
> -			   size_t *len)
> +			   size_t *len, int vnet_hdr_sz)
>  {
>  	struct virtio_net_hdr vnet_hdr;
> +	int ret;
>  
> -	if (*len < sizeof(vnet_hdr))
> +	if (*len < vnet_hdr_sz)
>  		return -EINVAL;
> -	*len -= sizeof(vnet_hdr);
> +	*len -= vnet_hdr_sz;
>  
>  	if (virtio_net_hdr_from_skb(skb, &vnet_hdr, vio_le(), true, 0))
>  		return -EINVAL;
>  
> -	return memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> +	ret = memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> +
> +	/* reserve space for extra info in vnet_hdr if needed */
> +	if (ret == 0)
> +		iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(vnet_hdr));
> +
> +	return ret;
>  }
>  
>  /*
> @@ -2311,7 +2318,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  				       (maclen < 16 ? 16 : maclen)) +
>  				       po->tp_reserve;
>  		if (po->has_vnet_hdr) {
> -			netoff += sizeof(struct virtio_net_hdr);
> +			netoff += po->vnet_hdr_sz;
>  			do_vnet = true;
>  		}
>  		macoff = netoff - maclen;
> @@ -2552,16 +2559,23 @@ static int __packet_snd_vnet_parse(struct virtio_net_hdr *vnet_hdr, size_t len)
>  }
>  
>  static int packet_snd_vnet_parse(struct msghdr *msg, size_t *len,
> -				 struct virtio_net_hdr *vnet_hdr)
> +				 struct virtio_net_hdr *vnet_hdr, int vnet_hdr_sz)
>  {
> -	if (*len < sizeof(*vnet_hdr))
> +	int ret;
> +
> +	if (*len < vnet_hdr_sz)
>  		return -EINVAL;
> -	*len -= sizeof(*vnet_hdr);
> +	*len -= vnet_hdr_sz;
>  
>  	if (!copy_from_iter_full(vnet_hdr, sizeof(*vnet_hdr), &msg->msg_iter))
>  		return -EFAULT;
>  
> -	return __packet_snd_vnet_parse(vnet_hdr, *len);
> +	ret = __packet_snd_vnet_parse(vnet_hdr, *len);
> +
> +	/* move iter to point to the start of mac header */
> +	if (ret == 0)
> +		iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(struct virtio_net_hdr));
> +	return ret;
>  }
>  
>  static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
> @@ -2730,6 +2744,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>  	int status = TP_STATUS_AVAILABLE;
>  	int hlen, tlen, copylen = 0;
>  	long timeo = 0;
> +	int vnet_hdr_sz;
>  
>  	mutex_lock(&po->pg_vec_lock);
>  
> @@ -2811,8 +2826,9 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>  		tlen = dev->needed_tailroom;
>  		if (po->has_vnet_hdr) {
>  			vnet_hdr = data;
> -			data += sizeof(*vnet_hdr);
> -			tp_len -= sizeof(*vnet_hdr);
> +			vnet_hdr_sz = po->vnet_hdr_sz;
> +			data += vnet_hdr_sz;
> +			tp_len -= vnet_hdr_sz;
>  			if (tp_len < 0 ||
>  			    __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
>  				tp_len = -EINVAL;
> @@ -2947,6 +2963,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>  	int offset = 0;
>  	struct packet_sock *po = pkt_sk(sk);
>  	bool has_vnet_hdr = false;
> +	int vnet_hdr_sz;
>  	int hlen, tlen, linear;
>  	int extra_len = 0;
>  
> @@ -2991,7 +3008,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>  	if (sock->type == SOCK_RAW)
>  		reserve = dev->hard_header_len;
>  	if (po->has_vnet_hdr) {
> -		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr);
> +		vnet_hdr_sz = po->vnet_hdr_sz;
> +		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr, vnet_hdr_sz);
>  		if (err)
>  			goto out_unlock;
>  		has_vnet_hdr = true;
> @@ -3068,7 +3086,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>  		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
>  		if (err)
>  			goto out_free;
> -		len += sizeof(vnet_hdr);
> +		len += vnet_hdr_sz;
>  		virtio_net_hdr_set_proto(skb, &vnet_hdr);
>  	}
>  
> @@ -3452,10 +3470,10 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  	packet_rcv_try_clear_pressure(pkt_sk(sk));
>  
>  	if (pkt_sk(sk)->has_vnet_hdr) {
> -		err = packet_rcv_vnet(msg, skb, &len);
> +		vnet_hdr_len = pkt_sk(sk)->vnet_hdr_sz;
> +		err = packet_rcv_vnet(msg, skb, &len, vnet_hdr_len);
>  		if (err)
>  			goto out_free;
> -		vnet_hdr_len = sizeof(struct virtio_net_hdr);
>  	}
>  
>  	/* You lose any data beyond the buffer you gave. If it worries
> -- 
> 1.8.3.1