// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * inet fragments management
 *
 *              Authors:        Pavel Emelyanov <xemul@openvz.org>
 *                              Started as consolidation of ipv4/ip_fragment.c,
 *                              ipv6/reassembly. and ipv6 nf conntrack reassembly
 */

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/slab.h>
#include <linux/rhashtable.h>

#include <net/sock.h>
#include <net/inet_frag.h>
#include <net/inet_ecn.h>
#include <net/ip.h>
#include <net/ipv6.h>

/* Use skb->cb to track consecutive/adjacent fragments coming at
 * the end of the queue. Nodes in the rb-tree queue will
 * contain "runs" of one or more adjacent fragments.
 *
 * Invariants:
 * - next_frag is NULL at the tail of a "run";
 * - the head of a "run" has the sum of all fragment lengths in frag_run_len.
 */
struct ipfrag_skb_cb {
        union {
                struct inet_skb_parm    h4;
                struct inet6_skb_parm   h6;
        };
        struct sk_buff          *next_frag;
        int                     frag_run_len;
};

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

static void fragcb_clear(struct sk_buff *skb)
{
        RB_CLEAR_NODE(&skb->rbnode);
        FRAG_CB(skb)->next_frag = NULL;
        FRAG_CB(skb)->frag_run_len = skb->len;
}

/* Append skb to the last "run". */
static void fragrun_append_to_last(struct inet_frag_queue *q,
                                   struct sk_buff *skb)
{
        fragcb_clear(skb);

        FRAG_CB(q->last_run_head)->frag_run_len += skb->len;
        FRAG_CB(q->fragments_tail)->next_frag = skb;
        q->fragments_tail = skb;
}

/* Create a new "run" with the skb. */
static void fragrun_create(struct inet_frag_queue *q, struct sk_buff *skb)
{
        BUILD_BUG_ON(sizeof(struct ipfrag_skb_cb) > sizeof(skb->cb));
        fragcb_clear(skb);

        if (q->last_run_head)
                rb_link_node(&skb->rbnode, &q->last_run_head->rbnode,
                             &q->last_run_head->rbnode.rb_right);
        else
                rb_link_node(&skb->rbnode, NULL, &q->rb_fragments.rb_node);
        rb_insert_color(&skb->rbnode, &q->rb_fragments);

        q->fragments_tail = skb;
        q->last_run_head = skb;
}

/* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
 * Value : 0xff if frame should be dropped.
 *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
 */
const u8 ip_frag_ecn_table[16] = {
        /* at least one fragment had CE, and others ECT_0 or ECT_1 */
        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]                      = INET_ECN_CE,
        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]                      = INET_ECN_CE,
        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]   = INET_ECN_CE,

        /* invalid combinations : drop frame */
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
};
EXPORT_SYMBOL(ip_frag_ecn_table);

int inet_frags_init(struct inet_frags *f)
{
        f->frags_cachep = kmem_cache_create(f->frags_cache_name, f->qsize, 0, 0,
                                            NULL);
        if (!f->frags_cachep)
                return -ENOMEM;

        return 0;
}
EXPORT_SYMBOL(inet_frags_init);

void inet_frags_fini(struct inet_frags *f)
{
        /* We must wait that all inet_frag_destroy_rcu() have completed. */
        rcu_barrier();

        kmem_cache_destroy(f->frags_cachep);
        f->frags_cachep = NULL;
}
EXPORT_SYMBOL(inet_frags_fini);

static void inet_frags_free_cb(void *ptr, void *arg)
{
        struct inet_frag_queue *fq = ptr;

        /* If we can not cancel the timer, it means this frag_queue
         * is already disappearing, we have nothing to do.
         * Otherwise, we own a refcount until the end of this function.
         */
        if (!del_timer(&fq->timer))
                return;

        spin_lock_bh(&fq->lock);
        if (!(fq->flags & INET_FRAG_COMPLETE)) {
                fq->flags |= INET_FRAG_COMPLETE;
                refcount_dec(&fq->refcnt);
        }
        spin_unlock_bh(&fq->lock);

        inet_frag_put(fq);
}

void inet_frags_exit_net(struct netns_frags *nf)
{
        nf->high_thresh = 0; /* prevent creation of new frags */

        rhashtable_free_and_destroy(&nf->rhashtable, inet_frags_free_cb, NULL);
}
EXPORT_SYMBOL(inet_frags_exit_net);

void inet_frag_kill(struct inet_frag_queue *fq)
{
        if (del_timer(&fq->timer))
                refcount_dec(&fq->refcnt);

        if (!(fq->flags & INET_FRAG_COMPLETE)) {
                struct netns_frags *nf = fq->net;

                fq->flags |= INET_FRAG_COMPLETE;
                rhashtable_remove_fast(&nf->rhashtable, &fq->node, nf->f->rhash_params);
                refcount_dec(&fq->refcnt);
        }
}
EXPORT_SYMBOL(inet_frag_kill);

static void inet_frag_destroy_rcu(struct rcu_head *head)
{
        struct inet_frag_queue *q = container_of(head, struct inet_frag_queue,
                                                 rcu);
        struct inet_frags *f = q->net->f;

        if (f->destructor)
                f->destructor(q);
        kmem_cache_free(f->frags_cachep, q);
}

unsigned int inet_frag_rbtree_purge(struct rb_root *root)
{
        struct rb_node *p = rb_first(root);
        unsigned int sum = 0;

        while (p) {
                struct sk_buff *skb = rb_entry(p, struct sk_buff, rbnode);

                p = rb_next(p);
                rb_erase(&skb->rbnode, root);
                while (skb) {
                        struct sk_buff *next = FRAG_CB(skb)->next_frag;

                        sum += skb->truesize;
                        kfree_skb(skb);
                        skb = next;
                }
        }
        return sum;
}
EXPORT_SYMBOL(inet_frag_rbtree_purge);

void inet_frag_destroy(struct inet_frag_queue *q)
{
        struct netns_frags *nf;
        unsigned int sum, sum_truesize = 0;
        struct inet_frags *f;

        WARN_ON(!(q->flags & INET_FRAG_COMPLETE));
        WARN_ON(del_timer(&q->timer) != 0);

        /* Release all fragment data. */
        nf = q->net;
        f = nf->f;
        sum_truesize = inet_frag_rbtree_purge(&q->rb_fragments);
        sum = sum_truesize + f->qsize;

        call_rcu(&q->rcu, inet_frag_destroy_rcu);

        sub_frag_mem_limit(nf, sum);
}
EXPORT_SYMBOL(inet_frag_destroy);

static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
                                               struct inet_frags *f,
                                               void *arg)
{
        struct inet_frag_queue *q;

        q = kmem_cache_zalloc(f->frags_cachep, GFP_ATOMIC);
        if (!q)
                return NULL;

        q->net = nf;
        f->constructor(q, arg);
        add_frag_mem_limit(nf, f->qsize);

        timer_setup(&q->timer, f->frag_expire, 0);
        spin_lock_init(&q->lock);
        refcount_set(&q->refcnt, 3);

        return q;
}

static struct inet_frag_queue *inet_frag_create(struct netns_frags *nf,
                                                void *arg,
                                                struct inet_frag_queue **prev)
{
        struct inet_frags *f = nf->f;
        struct inet_frag_queue *q;

        q = inet_frag_alloc(nf, f, arg);
        if (!q) {
                *prev = ERR_PTR(-ENOMEM);
                return NULL;
        }
        mod_timer(&q->timer, jiffies + nf->timeout);

        *prev = rhashtable_lookup_get_insert_key(&nf->rhashtable, &q->key,
                                                 &q->node, f->rhash_params);
        if (*prev) {
                q->flags |= INET_FRAG_COMPLETE;
                inet_frag_kill(q);
                inet_frag_destroy(q);
                return NULL;
        }
        return q;
}

/* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
struct inet_frag_queue *inet_frag_find(struct netns_frags *nf, void *key)
{
        struct inet_frag_queue *fq = NULL, *prev;

        if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh)
                return NULL;

        rcu_read_lock();

        prev = rhashtable_lookup(&nf->rhashtable, key, nf->f->rhash_params);
        if (!prev)
                fq = inet_frag_create(nf, key, &prev);
        if (prev && !IS_ERR(prev)) {
                fq = prev;
                if (!refcount_inc_not_zero(&fq->refcnt))
                        fq = NULL;
        }
        rcu_read_unlock();
        return fq;
}
EXPORT_SYMBOL(inet_frag_find);

int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
                           int offset, int end)
{
        struct sk_buff *last = q->fragments_tail;

        /* RFC5722, Section 4, amended by Errata ID : 3089
         *                          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) MUST be silently discarded.
         *
         * Duplicates, however, should be ignored (i.e. skb dropped, but the
         * queue/fragments kept for later reassembly).
         */
        if (!last)
                fragrun_create(q, skb);  /* First fragment. */
        else if (last->ip_defrag_offset + last->len < end) {
                /* This is the common case: skb goes to the end. */
                /* Detect and discard overlaps. */
                if (offset < last->ip_defrag_offset + last->len)
                        return IPFRAG_OVERLAP;
                if (offset == last->ip_defrag_offset + last->len)
                        fragrun_append_to_last(q, skb);
                else
                        fragrun_create(q, skb);
        } else {
                /* Binary search. Note that skb can become the first fragment,
                 * but not the last (covered above).
                 */
                struct rb_node **rbn, *parent;

                rbn = &q->rb_fragments.rb_node;
                do {
                        struct sk_buff *curr;
                        int curr_run_end;

                        parent = *rbn;
                        curr = rb_to_skb(parent);
                        curr_run_end = curr->ip_defrag_offset +
                                        FRAG_CB(curr)->frag_run_len;
                        if (end <= curr->ip_defrag_offset)
                                rbn = &parent->rb_left;
                        else if (offset >= curr_run_end)
                                rbn = &parent->rb_right;
                        else if (offset >= curr->ip_defrag_offset &&
                                 end <= curr_run_end)
                                return IPFRAG_DUP;
                        else
                                return IPFRAG_OVERLAP;
                } while (*rbn);
                /* Here we have parent properly set, and rbn pointing to
                 * one of its NULL left/right children. Insert skb.
                 */
                fragcb_clear(skb);
                rb_link_node(&skb->rbnode, parent, rbn);
                rb_insert_color(&skb->rbnode, &q->rb_fragments);
        }

        skb->ip_defrag_offset = offset;

        return IPFRAG_OK;
}
EXPORT_SYMBOL(inet_frag_queue_insert);

void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
                              struct sk_buff *parent)
{
        struct sk_buff *fp, *head = skb_rb_first(&q->rb_fragments);
        struct sk_buff **nextp;
        int delta;

        if (head != skb) {
                fp = skb_clone(skb, GFP_ATOMIC);
                if (!fp)
                        return NULL;
                FRAG_CB(fp)->next_frag = FRAG_CB(skb)->next_frag;
                if (RB_EMPTY_NODE(&skb->rbnode))
                        FRAG_CB(parent)->next_frag = fp;
                else
                        rb_replace_node(&skb->rbnode, &fp->rbnode,
                                        &q->rb_fragments);
                if (q->fragments_tail == skb)
                        q->fragments_tail = fp;
                skb_morph(skb, head);
                FRAG_CB(skb)->next_frag = FRAG_CB(head)->next_frag;
                rb_replace_node(&head->rbnode, &skb->rbnode,
                                &q->rb_fragments);
                consume_skb(head);
                head = skb;
        }
        WARN_ON(head->ip_defrag_offset != 0);

        delta = -head->truesize;

        /* Head of list must not be cloned. */
        if (skb_unclone(head, GFP_ATOMIC))
                return NULL;

        delta += head->truesize;
        if (delta)
                add_frag_mem_limit(q->net, delta);

        /* 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)
                        return NULL;
                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->data_len = head->data_len - plen;
                clone->len = clone->data_len;
                head->truesize += clone->truesize;
                clone->csum = 0;
                clone->ip_summed = head->ip_summed;
                add_frag_mem_limit(q->net, clone->truesize);
                skb_shinfo(head)->frag_list = clone;
                nextp = &clone->next;
        } else {
                nextp = &skb_shinfo(head)->frag_list;
        }

        return nextp;
}
EXPORT_SYMBOL(inet_frag_reasm_prepare);

void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
                            void *reasm_data)
{
        struct sk_buff **nextp = (struct sk_buff **)reasm_data;
        struct rb_node *rbn;
        struct sk_buff *fp;

        skb_push(head, head->data - skb_network_header(head));

        /* Traverse the tree in order, to build frag_list. */
        fp = FRAG_CB(head)->next_frag;
        rbn = rb_next(&head->rbnode);
        rb_erase(&head->rbnode, &q->rb_fragments);
        while (rbn || fp) {
                /* fp points to the next sk_buff in the current run;
                 * rbn points to the next run.
                 */
                /* Go through the current run. */
                while (fp) {
                        *nextp = fp;
                        nextp = &fp->next;
                        fp->prev = NULL;
                        memset(&fp->rbnode, 0, sizeof(fp->rbnode));
                        fp->sk = NULL;
                        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;
                        fp = FRAG_CB(fp)->next_frag;
                }
                /* Move to the next run. */
                if (rbn) {
                        struct rb_node *rbnext = rb_next(rbn);

                        fp = rb_to_skb(rbn);
                        rb_erase(rbn, &q->rb_fragments);
                        rbn = rbnext;
                }
        }
        sub_frag_mem_limit(q->net, head->truesize);

        *nextp = NULL;
        skb_mark_not_on_list(head);
        head->prev = NULL;
        head->tstamp = q->stamp;
}
EXPORT_SYMBOL(inet_frag_reasm_finish);

struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q)
{
        struct sk_buff *head, *skb;

        head = skb_rb_first(&q->rb_fragments);
        if (!head)
                return NULL;
        skb = FRAG_CB(head)->next_frag;
        if (skb)
                rb_replace_node(&head->rbnode, &skb->rbnode,
                                &q->rb_fragments);
        else
                rb_erase(&head->rbnode, &q->rb_fragments);
        memset(&head->rbnode, 0, sizeof(head->rbnode));
        barrier();

        if (head == q->fragments_tail)
                q->fragments_tail = NULL;

        sub_frag_mem_limit(q->net, head->truesize);

        return head;
}
EXPORT_SYMBOL(inet_frag_pull_head);