flow_dissector.c

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#include <linux/skbuff.h>
#include <linux/export.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/if_vlan.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <linux/if_tunnel.h>
#include <linux/if_pppox.h>
#include <linux/ppp_defs.h>
#include <net/flow_keys.h>

/* copy saddr & daddr, possibly using 64bit load/store
 * Equivalent to :  flow->src = iph->saddr;
 *          flow->dst = iph->daddr;
 */
static void iph_to_flow_copy_addrs(struct flow_keys *flow, const struct iphdr *iph)
{
    BUILD_BUG_ON(offsetof(typeof(*flow), dst) !=
             offsetof(typeof(*flow), src) + sizeof(flow->src));
    memcpy(&flow->src, &iph->saddr, sizeof(flow->src) + sizeof(flow->dst));
}

bool skb_flow_dissect(const struct sk_buff *skb, struct flow_keys *flow)
{
    int poff, nhoff = skb_network_offset(skb);
    u8 ip_proto;
    __be16 proto = skb->protocol;

    memset(flow, 0, sizeof(*flow));

again:
    switch (proto) {
    case __constant_htons(ETH_P_IP): {
        const struct iphdr *iph;
        struct iphdr _iph;
ip:
        iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
        if (!iph)
            return false;

        if (ip_is_fragment(iph))
            ip_proto = 0;
        else
            ip_proto = iph->protocol;
        iph_to_flow_copy_addrs(flow, iph);
        nhoff += iph->ihl * 4;
        break;
    }
    case __constant_htons(ETH_P_IPV6): {
        const struct ipv6hdr *iph;
        struct ipv6hdr _iph;
ipv6:
        iph = skb_header_pointer(skb, nhoff, sizeof(_iph), &_iph);
        if (!iph)
            return false;

        ip_proto = iph->nexthdr;
        flow->src = (__force __be32)ipv6_addr_hash(&iph->saddr);
        flow->dst = (__force __be32)ipv6_addr_hash(&iph->daddr);
        nhoff += sizeof(struct ipv6hdr);
        break;
    }
    case __constant_htons(ETH_P_8021Q): {
        const struct vlan_hdr *vlan;
        struct vlan_hdr _vlan;

        vlan = skb_header_pointer(skb, nhoff, sizeof(_vlan), &_vlan);
        if (!vlan)
            return false;

        proto = vlan->h_vlan_encapsulated_proto;
        nhoff += sizeof(*vlan);
        goto again;
    }
    case __constant_htons(ETH_P_PPP_SES): {
        struct {
            struct pppoe_hdr hdr;
            __be16 proto;
        } *hdr, _hdr;
        hdr = skb_header_pointer(skb, nhoff, sizeof(_hdr), &_hdr);
        if (!hdr)
            return false;
        proto = hdr->proto;
        nhoff += PPPOE_SES_HLEN;
        switch (proto) {
        case __constant_htons(PPP_IP):
            goto ip;
        case __constant_htons(PPP_IPV6):
            goto ipv6;
        default:
            return false;
        }
    }
    default:
        return false;
    }

    switch (ip_proto) {
    case IPPROTO_GRE: {
        struct gre_hdr {
            __be16 flags;
            __be16 proto;
        } *hdr, _hdr;

        hdr = skb_header_pointer(skb, nhoff, sizeof(_hdr), &_hdr);
        if (!hdr)
            return false;
        /*
         * Only look inside GRE if version zero and no
         * routing
         */
        if (!(hdr->flags & (GRE_VERSION|GRE_ROUTING))) {
            proto = hdr->proto;
            nhoff += 4;
            if (hdr->flags & GRE_CSUM)
                nhoff += 4;
            if (hdr->flags & GRE_KEY)
                nhoff += 4;
            if (hdr->flags & GRE_SEQ)
                nhoff += 4;
            goto again;
        }
        break;
    }
    case IPPROTO_IPIP:
        goto again;
    default:
        break;
    }

    flow->ip_proto = ip_proto;
    poff = proto_ports_offset(ip_proto);
    if (poff >= 0) {
        __be32 *ports, _ports;

        nhoff += poff;
        ports = skb_header_pointer(skb, nhoff, sizeof(_ports), &_ports);
        if (ports)
            flow->ports = *ports;
    }

    return true;
}
EXPORT_SYMBOL(skb_flow_dissect);