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Date:   Mon, 29 Apr 2019 15:49:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Willem de Bruijn' <willemdebruijn.kernel@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: RE: [PATCH net v2] packet: in recvmsg msg_name return at least sizeof
 sockaddr_ll

From: Willem de Bruijn
> Sent: 29 April 2019 16:47
> Packet send checks that msg_name is at least sizeof sockaddr_ll.
> Packet recv must return at least this length, so that its output
> can be passed unmodified to packet send.
> 
> This ceased to be true since adding support for lladdr longer than
> sll_addr. Since, the return value uses true address length.
> 
> Always return at least sizeof sockaddr_ll, even if address length
> is shorter. Zero the padding bytes.
> 
> Change v1->v2: do not overwrite zeroed padding again. use copy_len.
> 
> Fixes: 0fb375fb9b93 ("[AF_PACKET]: Allow for > 8 byte hardware addresses.")
> Suggested-by: David Laight <David.Laight@...lab.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/packet/af_packet.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index e726aaba73b9f..5fe3d75b6212d 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -3348,20 +3348,29 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  	sock_recv_ts_and_drops(msg, sk, skb);
> 
>  	if (msg->msg_name) {
> +		int copy_len;
> +
>  		/* If the address length field is there to be filled
>  		 * in, we fill it in now.
>  		 */
>  		if (sock->type == SOCK_PACKET) {
>  			__sockaddr_check_size(sizeof(struct sockaddr_pkt));
>  			msg->msg_namelen = sizeof(struct sockaddr_pkt);
> +			copy_len = msg->msg_namelen;
>  		} else {
>  			struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;
> 
>  			msg->msg_namelen = sll->sll_halen +
>  				offsetof(struct sockaddr_ll, sll_addr);
> +			copy_len = msg->msg_namelen;
> +			if (msg->msg_namelen < sizeof(struct sockaddr_ll)) {
> +				memset(msg->msg_name +
> +				       offsetof(struct sockaddr_ll, sll_addr),
> +				       0, sizeof(sll->sll_addr));
> +				msg->msg_namelen = sizeof(struct sockaddr_ll);
> +			}
>  		}
> -		memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa,
> -		       msg->msg_namelen);
> +		memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa, copy_len);
>  	}
> 
>  	if (pkt_sk(sk)->auxdata) {
> --
> 2.21.0.593.g511ec345e18-goog

Looks ok to me, not tried to compile it though.

	David

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