Re: [PATCH 4.16 008/161] packet: in packet_snd start writing at link layer allocation

[Tariq Toukan]

On 24/05/2018 12:37 PM, Greg Kroah-Hartman wrote:
> 4.16-stable review patch.  If anyone has any objections, please let me know.

Please hold on with this.
I think it causes some degradation.

I'll report the issue on the original patch.

Thanks,
Tariq

> ------------------
>
> From: Willem de Bruijn <willemb@xxxxxxxxxx>
>
> [ Upstream commit b84bbaf7a6c8cca24f8acf25a2c8e46913a947ba ]
>
> Packet sockets allow construction of packets shorter than
> dev->hard_header_len to accommodate protocols with variable length
> link layer headers. These packets are padded to dev->hard_header_len,
> because some device drivers interpret that as a minimum packet size.
>
> packet_snd reserves dev->hard_header_len bytes on allocation.
> SOCK_DGRAM sockets call skb_push in dev_hard_header() to ensure that
> link layer headers are stored in the reserved range. SOCK_RAW sockets
> do the same in tpacket_snd, but not in packet_snd.
>
> Syzbot was able to send a zero byte packet to a device with massive
> 116B link layer header, causing padding to cross over into skb_shinfo.
> Fix this by writing from the start of the llheader reserved range also
> in the case of packet_snd/SOCK_RAW.
>
> Update skb_set_network_header to the new offset. This also corrects
> it for SOCK_DGRAM, where it incorrectly double counted reserve due to
> the skb_push in dev_hard_header.
>
> Fixes: 9ed988cd5915 ("packet: validate variable length ll headers")
> Reported-by: syzbot+71d74a5406d02057d559@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>   net/packet/af_packet.c |    4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2903,13 +2903,15 @@ static int packet_snd(struct socket *soc
>   	if (skb == NULL)
>   		goto out_unlock;
>   
> -	skb_set_network_header(skb, reserve);
> +	skb_reset_network_header(skb);
>   
>   	err = -EINVAL;
>   	if (sock->type == SOCK_DGRAM) {
>   		offset = dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len);
>   		if (unlikely(offset < 0))
>   			goto out_free;
> +	} else if (reserve) {
> +		skb_push(skb, reserve);
>   	}
>   
>   	/* Returns -EFAULT on error */