netdev - RE: [PATCH net] packet: validate msg

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Date:   Mon, 29 Apr 2019 09:00:03 +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>,
        "idosch@...sch.org" <idosch@...sch.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: RE: [PATCH net] packet: validate msg_namelen in send directly

From: Willem de Bruijn
> Sent: 26 April 2019 20:28
> Packet sockets in datagram mode take a destination address. Verify its
> length before passing to dev_hard_header.
> 
> Prior to 2.6.14-rc3, the send code ignored sll_halen. This is
> established behavior. Directly compare msg_namelen to dev->addr_len.
> 
> Fixes: 6b8d95f1795c4 ("packet: validate address length if non-zero")
> Suggested-by: David Laight <David.Laight@...lab.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/packet/af_packet.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 9419c5cf4de5e..13301e36b4a28 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2624,10 +2624,13 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>  						sll_addr)))
>  			goto out;
>  		proto	= saddr->sll_protocol;
> -		addr	= saddr->sll_halen ? saddr->sll_addr : NULL;
>  		dev = dev_get_by_index(sock_net(&po->sk), saddr->sll_ifindex);
> -		if (addr && dev && saddr->sll_halen < dev->addr_len)
> -			goto out_put;
> +		if (po->sk.sk_socket->type == SOCK_DGRAM) {
> +			addr = saddr->sll_addr;
> +			if (dev && msg->msg_namelen < dev->addr_len +
> +					offsetof(struct sockaddr_ll, sll_addr))
> +				goto out_put;
> +		}

IIRC you need to initialise 'addr - NULL' at the top of the functions.
I'm surprised the compiler doesn't complain.

	David

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