From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next v6] Add Common Applications Kept Enhanced (cake)
 qdisc
Date: Tue, 1 May 2018 12:41:29 -0700
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On 05/01/2018 12:31 PM, Toke Høiland-Jørgensen wrote:

> Could you comment on specifically what you believe is broken in this,
> please, so I can fix it in the same iteration?
> 

Apart from the various pskb_may_pull() this helper should not change skb layout.

Ideally, the skb should be const and you would use skb_header_pointer() to make clear
you do not ever write this skb.

This would make the reviewer job pretty easy, as no side effect can possibly happen.


> +static inline struct tcphdr *cake_get_tcphdr(struct sk_buff *skb)
> +{
> +	struct ipv6hdr *ipv6h;
> +	struct iphdr *iph;
> +
> +	/* check IPv6 header size immediately, since for IPv4 we need the space
> +	 * for the TCP header anyway
> +	 */
> +	if (!pskb_may_pull(skb, skb_network_offset(skb) +
> +				sizeof(struct ipv6hdr)))
> +		return NULL;
> +
> +	iph = ip_hdr(skb);
> +
> +	if (iph->version == 4) {
> +		/* special-case 6in4 tunnelling, as that is a common way to get
> +		 * v6 connectivity in the home
> +		 */
> +		if (iph->protocol == IPPROTO_IPV6) {
> +			if (!pskb_may_pull(skb, (skb_network_offset(skb) +
> +						 ip_hdrlen(skb) +
> +						 sizeof(struct ipv6hdr))))
> +				return NULL;
> +
> +			ipv6h = (struct ipv6hdr *)(skb_network_header(skb) +
> +						   ip_hdrlen(skb));
> +
> +			if (ipv6h->nexthdr != IPPROTO_TCP)
> +				return NULL;
> +
> +			skb_set_inner_network_header(skb,
> +						     skb_network_offset(skb) +
> +						     ip_hdrlen(skb));
> +			skb_set_inner_transport_header(skb,
> +						skb_inner_network_offset(skb) +
> +						sizeof(struct ipv6hdr));

This is not allowed for a dissector.