/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              The IP fragmentation functionality.
 *              
 * Version:     $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
 *
 * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
 *              Alan Cox <Alan.Cox@linux.org>
 *
 * Fixes:
 *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
 *              David S. Miller :       Begin massive cleanup...
 *              Andi Kleen      :       Add sysctls.
 *              xxxx            :       Overlapfrag bug.
 *              Ultima          :       ip_expire() kernel panic.
 *              Bill Hawes      :       Frag accounting and evictor fixes.
 *              John McDonald   :       0 length frag bug.
 *              Alexey Kuznetsov:       SMP races, threading, cleanup.
 *              Patrick McHardy :       LRU queue of frag heads for evictor.
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/jiffies.h>
#include <linux/skbuff.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>

/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
 * as well. Or notify me, at least. --ANK
 */

/* Fragment cache limits. We will commit 256K at one time. Should we
 * cross that limit we will prune down to 192K. This should cope with
 * even the most extreme cases without allowing an attacker to measurably
 * harm machine performance.
 */
int sysctl_ipfrag_high_thresh = 256*1024;
int sysctl_ipfrag_low_thresh = 192*1024;

/* Important NOTE! Fragment queue must be destroyed before MSL expires.
 * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
 */
int sysctl_ipfrag_time = IP_FRAG_TIME;

struct ipfrag_skb_cb
{
        struct inet_skb_parm    h;
        int                     offset;
};

#define FRAG_CB(skb)    ((struct ipfrag_skb_cb*)((skb)->cb))

/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
        struct ipq      *next;          /* linked list pointers                 */
        struct list_head lru_list;      /* lru list member                      */
        u32             saddr;
        u32             daddr;
        u16             id;
        u8              protocol;
        u8              last_in;
#define COMPLETE                4
#define FIRST_IN                2
#define LAST_IN                 1

        struct sk_buff  *fragments;     /* linked list of received fragments    */
        int             len;            /* total length of original datagram    */
        int             meat;
        spinlock_t      lock;
        atomic_t        refcnt;
        struct timer_list timer;        /* when will this queue expire?         */
        struct ipq      **pprev;
        int             iif;
        struct timeval  stamp;
};

/* Hash table. */

#define IPQ_HASHSZ      64

/* Per-bucket lock is easy to add now. */
static struct ipq *ipq_hash[IPQ_HASHSZ];
static rwlock_t ipfrag_lock = RW_LOCK_UNLOCKED;
static u32 ipfrag_hash_rnd;
static LIST_HEAD(ipq_lru_list);
int ip_frag_nqueues = 0;

static __inline__ void __ipq_unlink(struct ipq *qp)
{
        if(qp->next)
                qp->next->pprev = qp->pprev;
        *qp->pprev = qp->next;
        list_del(&qp->lru_list);
        ip_frag_nqueues--;
}

static __inline__ void ipq_unlink(struct ipq *ipq)
{
        write_lock(&ipfrag_lock);
        __ipq_unlink(ipq);
        write_unlock(&ipfrag_lock);
}

static unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
{
        return jhash_3words((u32)id << 16 | prot, saddr, daddr,
                            ipfrag_hash_rnd) & (IPQ_HASHSZ - 1);
}

static struct timer_list ipfrag_secret_timer;
int sysctl_ipfrag_secret_interval = 10 * 60 * HZ;

static void ipfrag_secret_rebuild(unsigned long dummy)
{
        unsigned long now = jiffies;
        int i;

        write_lock(&ipfrag_lock);
        get_random_bytes(&ipfrag_hash_rnd, sizeof(u32));
        for (i = 0; i < IPQ_HASHSZ; i++) {
                struct ipq *q;

                q = ipq_hash[i];
                while (q) {
                        struct ipq *next = q->next;
                        unsigned int hval = ipqhashfn(q->id, q->saddr,
                                                      q->daddr, q->protocol);

                        if (hval != i) {
                                /* Unlink. */
                                if (q->next)
                                        q->next->pprev = q->pprev;
                                *q->pprev = q->next;

                                /* Relink to new hash chain. */
                                if ((q->next = ipq_hash[hval]) != NULL)
                                        q->next->pprev = &q->next;
                                ipq_hash[hval] = q;
                                q->pprev = &ipq_hash[hval];
                        }

                        q = next;
                }
        }
        write_unlock(&ipfrag_lock);

        mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval);
}

atomic_t ip_frag_mem = ATOMIC_INIT(0);  /* Memory used for fragments */

/* Memory Tracking Functions. */
static __inline__ void frag_kfree_skb(struct sk_buff *skb)
{
        atomic_sub(skb->truesize, &ip_frag_mem);
        kfree_skb(skb);
}

static __inline__ void frag_free_queue(struct ipq *qp)
{
        atomic_sub(sizeof(struct ipq), &ip_frag_mem);
        kfree(qp);
}

static __inline__ struct ipq *frag_alloc_queue(void)
{
        struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);

        if(!qp)
                return NULL;
        atomic_add(sizeof(struct ipq), &ip_frag_mem);
        return qp;
}


/* Destruction primitives. */

/* Complete destruction of ipq. */
static void ip_frag_destroy(struct ipq *qp)
{
        struct sk_buff *fp;

        BUG_TRAP(qp->last_in&COMPLETE);
        BUG_TRAP(del_timer(&qp->timer) == 0);

        /* Release all fragment data. */
        fp = qp->fragments;
        while (fp) {
                struct sk_buff *xp = fp->next;

                frag_kfree_skb(fp);
                fp = xp;
        }

        /* Finally, release the queue descriptor itself. */
        frag_free_queue(qp);
}

static __inline__ void ipq_put(struct ipq *ipq)
{
        if (atomic_dec_and_test(&ipq->refcnt))
                ip_frag_destroy(ipq);
}

/* Kill ipq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static void ipq_kill(struct ipq *ipq)
{
        if (del_timer(&ipq->timer))
                atomic_dec(&ipq->refcnt);

        if (!(ipq->last_in & COMPLETE)) {
                ipq_unlink(ipq);
                atomic_dec(&ipq->refcnt);
                ipq->last_in |= COMPLETE;
        }
}

/* Memory limiting on fragments.  Evictor trashes the oldest 
 * fragment queue until we are back under the low threshold.
 */
static void ip_evictor(void)
{
        struct ipq *qp;
        struct list_head *tmp;

        for(;;) {
                if (atomic_read(&ip_frag_mem) <= sysctl_ipfrag_low_thresh)
                        return;
                read_lock(&ipfrag_lock);
                if (list_empty(&ipq_lru_list)) {
                        read_unlock(&ipfrag_lock);
                        return;
                }
                tmp = ipq_lru_list.next;
                qp = list_entry(tmp, struct ipq, lru_list);
                atomic_inc(&qp->refcnt);
                read_unlock(&ipfrag_lock);

                spin_lock(&qp->lock);
                if (!(qp->last_in&COMPLETE))
                        ipq_kill(qp);
                spin_unlock(&qp->lock);

                ipq_put(qp);
                IP_INC_STATS_BH(IpReasmFails);
        }
}

/*
 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 */
static void ip_expire(unsigned long arg)
{
        struct ipq *qp = (struct ipq *) arg;

        spin_lock(&qp->lock);

        if (qp->last_in & COMPLETE)
                goto out;

        ipq_kill(qp);

        IP_INC_STATS_BH(IpReasmTimeout);
        IP_INC_STATS_BH(IpReasmFails);

        if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
                struct sk_buff *head = qp->fragments;
                /* Send an ICMP "Fragment Reassembly Timeout" message. */
                if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
                        icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
                        dev_put(head->dev);
                }
        }
out:
        spin_unlock(&qp->lock);
        ipq_put(qp);
}

/* Creation primitives. */

static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
{
        struct ipq *qp;

        write_lock(&ipfrag_lock);
#ifdef CONFIG_SMP
        /* With SMP race we have to recheck hash table, because
         * such entry could be created on other cpu, while we
         * promoted read lock to write lock.
         */
        for(qp = ipq_hash[hash]; qp; qp = qp->next) {
                if(qp->id == qp_in->id          &&
                   qp->saddr == qp_in->saddr    &&
                   qp->daddr == qp_in->daddr    &&
                   qp->protocol == qp_in->protocol) {
                        atomic_inc(&qp->refcnt);
                        write_unlock(&ipfrag_lock);
                        qp_in->last_in |= COMPLETE;
                        ipq_put(qp_in);
                        return qp;
                }
        }
#endif
        qp = qp_in;

        if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
                atomic_inc(&qp->refcnt);

        atomic_inc(&qp->refcnt);
        if((qp->next = ipq_hash[hash]) != NULL)
                qp->next->pprev = &qp->next;
        ipq_hash[hash] = qp;
        qp->pprev = &ipq_hash[hash];
        INIT_LIST_HEAD(&qp->lru_list);
        list_add_tail(&qp->lru_list, &ipq_lru_list);
        ip_frag_nqueues++;
        write_unlock(&ipfrag_lock);
        return qp;
}

/* Add an entry to the 'ipq' queue for a newly received IP datagram. */
static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph)
{
        struct ipq *qp;

        if ((qp = frag_alloc_queue()) == NULL)
                goto out_nomem;

        qp->protocol = iph->protocol;
        qp->last_in = 0;
        qp->id = iph->id;
        qp->saddr = iph->saddr;
        qp->daddr = iph->daddr;
        qp->len = 0;
        qp->meat = 0;
        qp->fragments = NULL;
        qp->iif = 0;

        /* Initialize a timer for this entry. */
        init_timer(&qp->timer);
        qp->timer.data = (unsigned long) qp;    /* pointer to queue     */
        qp->timer.function = ip_expire;         /* expire function      */
        qp->lock = SPIN_LOCK_UNLOCKED;
        atomic_set(&qp->refcnt, 1);

        return ip_frag_intern(hash, qp);

out_nomem:
        NETDEBUG(if (net_ratelimit()) printk(KERN_ERR "ip_frag_create: no memory left !\n"));
        return NULL;
}

/* Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and create new one, if nothing is found.
 */
static inline struct ipq *ip_find(struct iphdr *iph)
{
        __u16 id = iph->id;
        __u32 saddr = iph->saddr;
        __u32 daddr = iph->daddr;
        __u8 protocol = iph->protocol;
        unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
        struct ipq *qp;

        read_lock(&ipfrag_lock);
        for(qp = ipq_hash[hash]; qp; qp = qp->next) {
                if(qp->id == id         &&
                   qp->saddr == saddr   &&
                   qp->daddr == daddr   &&
                   qp->protocol == protocol) {
                        atomic_inc(&qp->refcnt);
                        read_unlock(&ipfrag_lock);
                        return qp;
                }
        }
        read_unlock(&ipfrag_lock);

        return ip_frag_create(hash, iph);
}

/* Add new segment to existing queue. */
static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
        struct sk_buff *prev, *next;
        int flags, offset;
        int ihl, end;

        if (qp->last_in & COMPLETE)
                goto err;

        offset = ntohs(skb->nh.iph->frag_off);
        flags = offset & ~IP_OFFSET;
        offset &= IP_OFFSET;
        offset <<= 3;           /* offset is in 8-byte chunks */
        ihl = skb->nh.iph->ihl * 4;

        /* Determine the position of this fragment. */
        end = offset + skb->len - ihl;

        /* Is this the final fragment? */
        if ((flags & IP_MF) == 0) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrrupted.
                 */
                if (end < qp->len ||
                    ((qp->last_in & LAST_IN) && end != qp->len))
                        goto err;
                qp->last_in |= LAST_IN;
                qp->len = end;
        } else {
                if (end&7) {
                        end &= ~7;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
                if (end > qp->len) {
                        /* Some bits beyond end -> corruption. */
                        if (qp->last_in & LAST_IN)
                                goto err;
                        qp->len = end;
                }
        }
        if (end == offset)
                goto err;

        if (pskb_pull(skb, ihl) == NULL)
                goto err;
        if (pskb_trim(skb, end-offset))
                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 = NULL;
        for(next = qp->fragments; next != NULL; next = next->next) {
                if (FRAG_CB(next)->offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }

        /* We found where to put this one.  Check for overlap with
         * preceding fragment, and, if needed, align things so that
         * any overlaps are eliminated.
         */
        if (prev) {
                int i = (FRAG_CB(prev)->offset + prev->len) - offset;

                if (i > 0) {
                        offset += i;
                        if (end <= offset)
                                goto err;
                        if (!pskb_pull(skb, i))
                                goto err;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
        }

        while (next && FRAG_CB(next)->offset < end) {
                int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */

                if (i < next->len) {
                        /* Eat head of the next overlapped fragment
                         * and leave the loop. The next ones cannot overlap.
                         */
                        if (!pskb_pull(next, i))
                                goto err;
                        FRAG_CB(next)->offset += i;
                        qp->meat -= i;
                        if (next->ip_summed != CHECKSUM_UNNECESSARY)
                                next->ip_summed = CHECKSUM_NONE;
                        break;
                } else {
                        struct sk_buff *free_it = next;

                        /* Old fragmnet is completely overridden with
                         * new one drop it.
                         */
                        next = next->next;

                        if (prev)
                                prev->next = next;
                        else
                                qp->fragments = next;

                        qp->meat -= free_it->len;
                        frag_kfree_skb(free_it);
                }
        }

        FRAG_CB(skb)->offset = offset;

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

        if (skb->dev)
                qp->iif = skb->dev->ifindex;
        skb->dev = NULL;
        qp->stamp = skb->stamp;
        qp->meat += skb->len;
        atomic_add(skb->truesize, &ip_frag_mem);
        if (offset == 0)
                qp->last_in |= FIRST_IN;

        write_lock(&ipfrag_lock);
        list_move_tail(&qp->lru_list, &ipq_lru_list);
        write_unlock(&ipfrag_lock);

        return;

err:
        kfree_skb(skb);
}


/* Build a new IP datagram from all its fragments. */

static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
{
        struct iphdr *iph;
        struct sk_buff *fp, *head = qp->fragments;
        int len;
        int ihlen;

        ipq_kill(qp);

        BUG_TRAP(head != NULL);
        BUG_TRAP(FRAG_CB(head)->offset == 0);

        /* Allocate a new buffer for the datagram. */
        ihlen = head->nh.iph->ihl*4;
        len = ihlen + qp->len;

        if(len > 65535)
                goto out_oversize;

        /* Head of list must not be cloned. */
        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
                goto out_nomem;

        /* 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_shinfo(head)->frag_list) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
                        goto out_nomem;
                clone->next = head->next;
                head->next = clone;
                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
                skb_shinfo(head)->frag_list = NULL;
                for (i=0; i<skb_shinfo(head)->nr_frags; i++)
                        plen += skb_shinfo(head)->frags[i].size;
                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;
                atomic_add(clone->truesize, &ip_frag_mem);
        }

        skb_shinfo(head)->frag_list = head->next;
        skb_push(head, head->data - head->nh.raw);
        atomic_sub(head->truesize, &ip_frag_mem);

        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_HW)
                        head->csum = csum_add(head->csum, fp->csum);
                head->truesize += fp->truesize;
                atomic_sub(fp->truesize, &ip_frag_mem);
        }

        head->next = NULL;
        head->dev = dev;
        head->stamp = qp->stamp;

        iph = head->nh.iph;
        iph->frag_off = 0;
        iph->tot_len = htons(len);
        IP_INC_STATS_BH(IpReasmOKs);
        qp->fragments = NULL;
        return head;

out_nomem:
        NETDEBUG(if (net_ratelimit())
                 printk(KERN_ERR 
                        "IP: queue_glue: no memory for gluing queue %p\n",
                        qp));
        goto out_fail;
out_oversize:
        if (net_ratelimit())
                printk(KERN_INFO
                        "Oversized IP packet from %d.%d.%d.%d.\n",
                        NIPQUAD(qp->saddr));
out_fail:
        IP_INC_STATS_BH(IpReasmFails);
        return NULL;
}

/* Process an incoming IP datagram fragment. */
struct sk_buff *ip_defrag(struct sk_buff *skb)
{
        struct iphdr *iph = skb->nh.iph;
        struct ipq *qp;
        struct net_device *dev;
        
        IP_INC_STATS_BH(IpReasmReqds);

        /* Start by cleaning up the memory. */
        if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
                ip_evictor();

        dev = skb->dev;

        /* Lookup (or create) queue header */
        if ((qp = ip_find(iph)) != NULL) {
                struct sk_buff *ret = NULL;

                spin_lock(&qp->lock);

                ip_frag_queue(qp, skb);

                if (qp->last_in == (FIRST_IN|LAST_IN) &&
                    qp->meat == qp->len)
                        ret = ip_frag_reasm(qp, dev);

                spin_unlock(&qp->lock);
                ipq_put(qp);
                return ret;
        }

        IP_INC_STATS_BH(IpReasmFails);
        kfree_skb(skb);
        return NULL;
}

void ipfrag_init(void)
{
        ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
                                 (jiffies ^ (jiffies >> 6)));

        init_timer(&ipfrag_secret_timer);
        ipfrag_secret_timer.function = ipfrag_secret_rebuild;
        ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval;
        add_timer(&ipfrag_secret_timer);
}

EXPORT_SYMBOL(ip_defrag);