nf_conntrack_reasm.c

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/*
 * IPv6 fragment reassembly for connection tracking
 *
 * Copyright (C)2004 USAGI/WIDE Project
 *
 * Author:
 *  Yasuyuki Kozakai @USAGI <[email protected]>
 *
 * Based on: net/ipv6/reassembly.c
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/jiffies.h>
#include <linux/net.h>
#include <linux/list.h>
#include <linux/netdevice.h>
#include <linux/in6.h>
#include <linux/ipv6.h>
#include <linux/icmpv6.h>
#include <linux/random.h>
#include <linux/slab.h>

#include <net/sock.h>
#include <net/snmp.h>
#include <net/inet_frag.h>

#include <net/ipv6.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/rawv6.h>
#include <net/ndisc.h>
#include <net/addrconf.h>
#include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
#include <linux/sysctl.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <net/netfilter/ipv6/nf_defrag_ipv6.h>


struct nf_ct_frag6_skb_cb
{
    struct inet6_skb_parm   h;
    int         offset;
    struct sk_buff      *orig;
};

#define NFCT_FRAG6_CB(skb)  ((struct nf_ct_frag6_skb_cb*)((skb)->cb))

static struct inet_frags nf_frags;

#ifdef CONFIG_SYSCTL
static struct ctl_table nf_ct_frag6_sysctl_table[] = {
    {
        .procname   = "nf_conntrack_frag6_timeout",
        .data       = &init_net.nf_frag.frags.timeout,
        .maxlen     = sizeof(unsigned int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec_jiffies,
    },
    {
        .procname   = "nf_conntrack_frag6_low_thresh",
        .data       = &init_net.nf_frag.frags.low_thresh,
        .maxlen     = sizeof(unsigned int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec,
    },
    {
        .procname   = "nf_conntrack_frag6_high_thresh",
        .data       = &init_net.nf_frag.frags.high_thresh,
        .maxlen     = sizeof(unsigned int),
        .mode       = 0644,
        .proc_handler   = proc_dointvec,
    },
    { }
};

static int nf_ct_frag6_sysctl_register(struct net *net)
{
    struct ctl_table *table;
    struct ctl_table_header *hdr;

    table = nf_ct_frag6_sysctl_table;
    if (!net_eq(net, &init_net)) {
        table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
                GFP_KERNEL);
        if (table == NULL)
            goto err_alloc;

        table[0].data = &net->ipv6.frags.high_thresh;
        table[1].data = &net->ipv6.frags.low_thresh;
        table[2].data = &net->ipv6.frags.timeout;
    }

    hdr = register_net_sysctl(net, "net/netfilter", table);
    if (hdr == NULL)
        goto err_reg;

    net->nf_frag.sysctl.frags_hdr = hdr;
    return 0;

err_reg:
    if (!net_eq(net, &init_net))
        kfree(table);
err_alloc:
    return -ENOMEM;
}

static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
{
    struct ctl_table *table;

    table = net->nf_frag.sysctl.frags_hdr->ctl_table_arg;
    unregister_net_sysctl_table(net->nf_frag.sysctl.frags_hdr);
    if (!net_eq(net, &init_net))
        kfree(table);
}

#else
static int nf_ct_frag6_sysctl_register(struct net *net)
{
    return 0;
}
static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
{
}
#endif

static unsigned int nf_hashfn(struct inet_frag_queue *q)
{
    const struct frag_queue *nq;

    nq = container_of(q, struct frag_queue, q);
    return inet6_hash_frag(nq->id, &nq->saddr, &nq->daddr, nf_frags.rnd);
}

static void nf_skb_free(struct sk_buff *skb)
{
    if (NFCT_FRAG6_CB(skb)->orig)
        kfree_skb(NFCT_FRAG6_CB(skb)->orig);
}

static void nf_ct_frag6_expire(unsigned long data)
{
    struct frag_queue *fq;
    struct net *net;

    fq = container_of((struct inet_frag_queue *)data, struct frag_queue, q);
    net = container_of(fq->q.net, struct net, nf_frag.frags);

    ip6_expire_frag_queue(net, fq, &nf_frags);
}

/* Creation primitives. */
static inline struct frag_queue *fq_find(struct net *net, __be32 id,
                     u32 user, struct in6_addr *src,
                     struct in6_addr *dst)
{
    struct inet_frag_queue *q;
    struct ip6_create_arg arg;
    unsigned int hash;

    arg.id = id;
    arg.user = user;
    arg.src = src;
    arg.dst = dst;

    read_lock_bh(&nf_frags.lock);
    hash = inet6_hash_frag(id, src, dst, nf_frags.rnd);

    q = inet_frag_find(&net->nf_frag.frags, &nf_frags, &arg, hash);
    local_bh_enable();
    if (q == NULL)
        goto oom;

    return container_of(q, struct frag_queue, q);

oom:
    return NULL;
}


static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
                 const struct frag_hdr *fhdr, int nhoff)
{
    struct sk_buff *prev, *next;
    unsigned int payload_len;
    int offset, end;

    if (fq->q.last_in & INET_FRAG_COMPLETE) {
        pr_debug("Already completed\n");
        goto err;
    }

    payload_len = ntohs(ipv6_hdr(skb)->payload_len);

    offset = ntohs(fhdr->frag_off) & ~0x7;
    end = offset + (payload_len -
            ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

    if ((unsigned int)end > IPV6_MAXPLEN) {
        pr_debug("offset is too large.\n");
        return -1;
    }

    if (skb->ip_summed == CHECKSUM_COMPLETE) {
        const unsigned char *nh = skb_network_header(skb);
        skb->csum = csum_sub(skb->csum,
                     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
                          0));
    }

    /* Is this the final fragment? */
    if (!(fhdr->frag_off & htons(IP6_MF))) {
        /* If we already have some bits beyond end
         * or have different end, the segment is corrupted.
         */
        if (end < fq->q.len ||
            ((fq->q.last_in & INET_FRAG_LAST_IN) && end != fq->q.len)) {
            pr_debug("already received last fragment\n");
            goto err;
        }
        fq->q.last_in |= INET_FRAG_LAST_IN;
        fq->q.len = end;
    } else {
        /* Check if the fragment is rounded to 8 bytes.
         * Required by the RFC.
         */
        if (end & 0x7) {
            /* RFC2460 says always send parameter problem in
             * this case. -DaveM
             */
            pr_debug("end of fragment not rounded to 8 bytes.\n");
            return -1;
        }
        if (end > fq->q.len) {
            /* Some bits beyond end -> corruption. */
            if (fq->q.last_in & INET_FRAG_LAST_IN) {
                pr_debug("last packet already reached.\n");
                goto err;
            }
            fq->q.len = end;
        }
    }

    if (end == offset)
        goto err;

    /* Point into the IP datagram 'data' part. */
    if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
        pr_debug("queue: message is too short.\n");
        goto err;
    }
    if (pskb_trim_rcsum(skb, end - offset)) {
        pr_debug("Can't trim\n");
        goto err;
    }

    /* Find out which fragments are in front and at the back of us
     * in the chain of fragments so far.  We must know where to put
     * this fragment, right?
     */
    prev = fq->q.fragments_tail;
    if (!prev || NFCT_FRAG6_CB(prev)->offset < offset) {
        next = NULL;
        goto found;
    }
    prev = NULL;
    for (next = fq->q.fragments; next != NULL; next = next->next) {
        if (NFCT_FRAG6_CB(next)->offset >= offset)
            break;  /* bingo! */
        prev = next;
    }

found:
    /* RFC5722, Section 4:
     *                                  When reassembling an IPv6 datagram, if
     *   one or more its constituent fragments is determined to be an
     *   overlapping fragment, the entire datagram (and any constituent
     *   fragments, including those not yet received) MUST be silently
     *   discarded.
     */

    /* Check for overlap with preceding fragment. */
    if (prev &&
        (NFCT_FRAG6_CB(prev)->offset + prev->len) > offset)
        goto discard_fq;

    /* Look for overlap with succeeding segment. */
    if (next && NFCT_FRAG6_CB(next)->offset < end)
        goto discard_fq;

    NFCT_FRAG6_CB(skb)->offset = offset;

    /* Insert this fragment in the chain of fragments. */
    skb->next = next;
    if (!next)
        fq->q.fragments_tail = skb;
    if (prev)
        prev->next = skb;
    else
        fq->q.fragments = skb;

    skb->dev = NULL;
    fq->q.stamp = skb->tstamp;
    fq->q.meat += skb->len;
    if (payload_len > fq->q.max_size)
        fq->q.max_size = payload_len;
    atomic_add(skb->truesize, &fq->q.net->mem);

    /* The first fragment.
     * nhoffset is obtained from the first fragment, of course.
     */
    if (offset == 0) {
        fq->nhoffset = nhoff;
        fq->q.last_in |= INET_FRAG_FIRST_IN;
    }
    write_lock(&nf_frags.lock);
    list_move_tail(&fq->q.lru_list, &fq->q.net->lru_list);
    write_unlock(&nf_frags.lock);
    return 0;

discard_fq:
    inet_frag_kill(&fq->q, &nf_frags);
err:
    return -1;
}

/*
 *  Check if this packet is complete.
 *  Returns NULL on failure by any reason, and pointer
 *  to current nexthdr field in reassembled frame.
 *
 *  It is called with locked fq, and caller must check that
 *  queue is eligible for reassembly i.e. it is not COMPLETE,
 *  the last and the first frames arrived and all the bits are here.
 */
static struct sk_buff *
nf_ct_frag6_reasm(struct frag_queue *fq, struct net_device *dev)
{
    struct sk_buff *fp, *op, *head = fq->q.fragments;
    int    payload_len;

    inet_frag_kill(&fq->q, &nf_frags);

    WARN_ON(head == NULL);
    WARN_ON(NFCT_FRAG6_CB(head)->offset != 0);

    /* Unfragmented part is taken from the first segment. */
    payload_len = ((head->data - skb_network_header(head)) -
               sizeof(struct ipv6hdr) + fq->q.len -
               sizeof(struct frag_hdr));
    if (payload_len > IPV6_MAXPLEN) {
        pr_debug("payload len is too large.\n");
        goto out_oversize;
    }

    /* Head of list must not be cloned. */
    if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
        pr_debug("skb is cloned but can't expand head");
        goto out_oom;
    }

    /* If the first fragment is fragmented itself, we split
     * it to two chunks: the first with data and paged part
     * and the second, holding only fragments. */
    if (skb_has_frag_list(head)) {
        struct sk_buff *clone;
        int i, plen = 0;

        clone = alloc_skb(0, GFP_ATOMIC);
        if (clone == NULL)
            goto out_oom;

        clone->next = head->next;
        head->next = clone;
        skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
        skb_frag_list_init(head);
        for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
            plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
        clone->len = clone->data_len = head->data_len - plen;
        head->data_len -= clone->len;
        head->len -= clone->len;
        clone->csum = 0;
        clone->ip_summed = head->ip_summed;

        NFCT_FRAG6_CB(clone)->orig = NULL;
        atomic_add(clone->truesize, &fq->q.net->mem);
    }

    /* We have to remove fragment header from datagram and to relocate
     * header in order to calculate ICV correctly. */
    skb_network_header(head)[fq->nhoffset] = skb_transport_header(head)[0];
    memmove(head->head + sizeof(struct frag_hdr), head->head,
        (head->data - head->head) - sizeof(struct frag_hdr));
    head->mac_header += sizeof(struct frag_hdr);
    head->network_header += sizeof(struct frag_hdr);

    skb_shinfo(head)->frag_list = head->next;
    skb_reset_transport_header(head);
    skb_push(head, head->data - skb_network_header(head));

    for (fp=head->next; fp; fp = fp->next) {
        head->data_len += fp->len;
        head->len += fp->len;
        if (head->ip_summed != fp->ip_summed)
            head->ip_summed = CHECKSUM_NONE;
        else if (head->ip_summed == CHECKSUM_COMPLETE)
            head->csum = csum_add(head->csum, fp->csum);
        head->truesize += fp->truesize;
    }
    atomic_sub(head->truesize, &fq->q.net->mem);

    head->local_df = 1;
    head->next = NULL;
    head->dev = dev;
    head->tstamp = fq->q.stamp;
    ipv6_hdr(head)->payload_len = htons(payload_len);
    IP6CB(head)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;

    /* Yes, and fold redundant checksum back. 8) */
    if (head->ip_summed == CHECKSUM_COMPLETE)
        head->csum = csum_partial(skb_network_header(head),
                      skb_network_header_len(head),
                      head->csum);

    fq->q.fragments = NULL;
    fq->q.fragments_tail = NULL;

    /* all original skbs are linked into the NFCT_FRAG6_CB(head).orig */
    fp = skb_shinfo(head)->frag_list;
    if (fp && NFCT_FRAG6_CB(fp)->orig == NULL)
        /* at above code, head skb is divided into two skbs. */
        fp = fp->next;

    op = NFCT_FRAG6_CB(head)->orig;
    for (; fp; fp = fp->next) {
        struct sk_buff *orig = NFCT_FRAG6_CB(fp)->orig;

        op->next = orig;
        op = orig;
        NFCT_FRAG6_CB(fp)->orig = NULL;
    }

    return head;

out_oversize:
    net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
                payload_len);
    goto out_fail;
out_oom:
    net_dbg_ratelimited("nf_ct_frag6_reasm: no memory for reassembly\n");
out_fail:
    return NULL;
}

/*
 * find the header just before Fragment Header.
 *
 * if success return 0 and set ...
 * (*prevhdrp): the value of "Next Header Field" in the header
 *      just before Fragment Header.
 * (*prevhoff): the offset of "Next Header Field" in the header
 *      just before Fragment Header.
 * (*fhoff)   : the offset of Fragment Header.
 *
 * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
 *
 */
static int
find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
{
    u8 nexthdr = ipv6_hdr(skb)->nexthdr;
    const int netoff = skb_network_offset(skb);
    u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
    int start = netoff + sizeof(struct ipv6hdr);
    int len = skb->len - start;
    u8 prevhdr = NEXTHDR_IPV6;

    while (nexthdr != NEXTHDR_FRAGMENT) {
        struct ipv6_opt_hdr hdr;
        int hdrlen;

        if (!ipv6_ext_hdr(nexthdr)) {
            return -1;
        }
        if (nexthdr == NEXTHDR_NONE) {
            pr_debug("next header is none\n");
            return -1;
        }
        if (len < (int)sizeof(struct ipv6_opt_hdr)) {
            pr_debug("too short\n");
            return -1;
        }
        if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
            BUG();
        if (nexthdr == NEXTHDR_AUTH)
            hdrlen = (hdr.hdrlen+2)<<2;
        else
            hdrlen = ipv6_optlen(&hdr);

        prevhdr = nexthdr;
        prev_nhoff = start;

        nexthdr = hdr.nexthdr;
        len -= hdrlen;
        start += hdrlen;
    }

    if (len < 0)
        return -1;

    *prevhdrp = prevhdr;
    *prevhoff = prev_nhoff;
    *fhoff = start;

    return 0;
}

struct sk_buff *nf_ct_frag6_gather(struct sk_buff *skb, u32 user)
{
    struct sk_buff *clone;
    struct net_device *dev = skb->dev;
    struct net *net = skb_dst(skb) ? dev_net(skb_dst(skb)->dev)
                       : dev_net(skb->dev);
    struct frag_hdr *fhdr;
    struct frag_queue *fq;
    struct ipv6hdr *hdr;
    int fhoff, nhoff;
    u8 prevhdr;
    struct sk_buff *ret_skb = NULL;

    /* Jumbo payload inhibits frag. header */
    if (ipv6_hdr(skb)->payload_len == 0) {
        pr_debug("payload len = 0\n");
        return skb;
    }

    if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
        return skb;

    clone = skb_clone(skb, GFP_ATOMIC);
    if (clone == NULL) {
        pr_debug("Can't clone skb\n");
        return skb;
    }

    NFCT_FRAG6_CB(clone)->orig = skb;

    if (!pskb_may_pull(clone, fhoff + sizeof(*fhdr))) {
        pr_debug("message is too short.\n");
        goto ret_orig;
    }

    skb_set_transport_header(clone, fhoff);
    hdr = ipv6_hdr(clone);
    fhdr = (struct frag_hdr *)skb_transport_header(clone);

    local_bh_disable();
    inet_frag_evictor(&net->nf_frag.frags, &nf_frags, false);
    local_bh_enable();

    fq = fq_find(net, fhdr->identification, user, &hdr->saddr, &hdr->daddr);
    if (fq == NULL) {
        pr_debug("Can't find and can't create new queue\n");
        goto ret_orig;
    }

    spin_lock_bh(&fq->q.lock);

    if (nf_ct_frag6_queue(fq, clone, fhdr, nhoff) < 0) {
        spin_unlock_bh(&fq->q.lock);
        pr_debug("Can't insert skb to queue\n");
        inet_frag_put(&fq->q, &nf_frags);
        goto ret_orig;
    }

    if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
        fq->q.meat == fq->q.len) {
        ret_skb = nf_ct_frag6_reasm(fq, dev);
        if (ret_skb == NULL)
            pr_debug("Can't reassemble fragmented packets\n");
    }
    spin_unlock_bh(&fq->q.lock);

    inet_frag_put(&fq->q, &nf_frags);
    return ret_skb;

ret_orig:
    kfree_skb(clone);
    return skb;
}

void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb,
            struct net_device *in, struct net_device *out,
            int (*okfn)(struct sk_buff *))
{
    struct sk_buff *s, *s2;
    unsigned int ret = 0;

    for (s = NFCT_FRAG6_CB(skb)->orig; s;) {
        nf_conntrack_put_reasm(s->nfct_reasm);
        nf_conntrack_get_reasm(skb);
        s->nfct_reasm = skb;

        s2 = s->next;
        s->next = NULL;

        if (ret != -ECANCELED)
            ret = NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s,
                         in, out, okfn,
                         NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
        else
            kfree_skb(s);

        s = s2;
    }
    nf_conntrack_put_reasm(skb);
}

static int nf_ct_net_init(struct net *net)
{
    net->nf_frag.frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
    net->nf_frag.frags.low_thresh = IPV6_FRAG_LOW_THRESH;
    net->nf_frag.frags.timeout = IPV6_FRAG_TIMEOUT;
    inet_frags_init_net(&net->nf_frag.frags);

    return nf_ct_frag6_sysctl_register(net);
}

static void nf_ct_net_exit(struct net *net)
{
    nf_ct_frags6_sysctl_unregister(net);
    inet_frags_exit_net(&net->nf_frag.frags, &nf_frags);
}

static struct pernet_operations nf_ct_net_ops = {
    .init = nf_ct_net_init,
    .exit = nf_ct_net_exit,
};

int nf_ct_frag6_init(void)
{
    int ret = 0;

    nf_frags.hashfn = nf_hashfn;
    nf_frags.constructor = ip6_frag_init;
    nf_frags.destructor = NULL;
    nf_frags.skb_free = nf_skb_free;
    nf_frags.qsize = sizeof(struct frag_queue);
    nf_frags.match = ip6_frag_match;
    nf_frags.frag_expire = nf_ct_frag6_expire;
    nf_frags.secret_interval = 10 * 60 * HZ;
    inet_frags_init(&nf_frags);

    ret = register_pernet_subsys(&nf_ct_net_ops);
    if (ret)
        inet_frags_fini(&nf_frags);

    return ret;
}

void nf_ct_frag6_cleanup(void)
{
    unregister_pernet_subsys(&nf_ct_net_ops);
    inet_frags_fini(&nf_frags);
}