Re: [PATCH] ipv4/ip_gre: make ipgre_tunnel_xmit() not parse network header as IP unconditionally

[Eric Dumazet <eric.dumazet@gmail.com>]

On Fri, 2012-12-21 at 10:12 +0900, Isaku Yamahata wrote:
> ipgre_tunnel_xmit() parses network header as IP unconditionally.
> But transmitting packets are not always IP packet. For example such packet
> can be sent by packet socket with sockaddr_ll.sll_protocol set.
> So make the function check if skb->protocol is IP.
> 
> Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
> ---
>  net/ipv4/ip_gre.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> index a85ae2f..8fcf0ed 100644
> --- a/net/ipv4/ip_gre.c
> +++ b/net/ipv4/ip_gre.c
> @@ -760,7 +760,10 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
>  
>  	if (dev->header_ops && dev->type == ARPHRD_IPGRE) {
>  		gre_hlen = 0;
> -		tiph = (const struct iphdr *)skb->data;
> +		if (skb->protocol == htons(ETH_P_IP))
> +			tiph = (const struct iphdr *)skb->data;
> +		else
> +			tiph = &tunnel->parms.iph;
>  	} else {
>  		gre_hlen = tunnel->hlen;
>  		tiph = &tunnel->parms.iph;

Seems good to me thanks !

Acked-by: Eric Dumazet <edumazet@google.com>

BTW, it seems another bug exists at line 931 : We dereference tiph while
it could point to freed memory because of the skb_realloc_headroom() at
line 893

I'll send a patch.