// SPDX-License-Identifier: GPL-2.0
/*
 * 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.
 *
 * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
 *              Alan Cox <alan@lxorguk.ukuu.org.uk>
 *
 * 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.
 */

#define pr_fmt(fmt) "IPv4: " fmt

#include <linux/compiler.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 <linux/slab.h>
#include <net/route.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <net/inetpeer.h>
#include <net/inet_frag.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>
#include <net/inet_ecn.h>
#include <net/l3mdev.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
 */
static const char ip_frag_cache_name[] = "ip4-frags";

/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
        struct inet_frag_queue q;

        u8              ecn; /* RFC3168 support */
        u16             max_df_size; /* largest frag with DF set seen */
        int             iif;
        unsigned int    rid;
        struct inet_peer *peer;
};

static u8 ip4_frag_ecn(u8 tos)
{
        return 1 << (tos & INET_ECN_MASK);
}

static struct inet_frags ip4_frags;

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
                         struct sk_buff *prev_tail, struct net_device *dev,
                         int *refs);


static void ip4_frag_init(struct inet_frag_queue *q, const void *a)
{
        struct ipq *qp = container_of(q, struct ipq, q);
        const struct frag_v4_compare_key *key = a;
        struct net *net = q->fqdir->net;
        struct inet_peer *p = NULL;

        q->key.v4 = *key;
        qp->ecn = 0;
        if (q->fqdir->max_dist) {
                rcu_read_lock();
                p = inet_getpeer_v4(net->ipv4.peers, key->saddr, key->vif);
                if (p && !refcount_inc_not_zero(&p->refcnt))
                        p = NULL;
                rcu_read_unlock();
        }
        qp->peer = p;
}

static void ip4_frag_free(struct inet_frag_queue *q)
{
        struct ipq *qp;

        qp = container_of(q, struct ipq, q);
        if (qp->peer)
                inet_putpeer(qp->peer);
}

static bool frag_expire_skip_icmp(u32 user)
{
        return user == IP_DEFRAG_AF_PACKET ||
               ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_IN,
                                         __IP_DEFRAG_CONNTRACK_IN_END) ||
               ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_BRIDGE_IN,
                                         __IP_DEFRAG_CONNTRACK_BRIDGE_IN);
}

/*
 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 */
static void ip_expire(struct timer_list *t)
{
        enum skb_drop_reason reason = SKB_DROP_REASON_FRAG_REASM_TIMEOUT;
        struct inet_frag_queue *frag = timer_container_of(frag, t, timer);
        const struct iphdr *iph;
        struct sk_buff *head = NULL;
        struct net *net;
        struct ipq *qp;
        int refs = 1;

        qp = container_of(frag, struct ipq, q);
        net = qp->q.fqdir->net;

        rcu_read_lock();
        spin_lock(&qp->q.lock);

        if (qp->q.flags & INET_FRAG_COMPLETE)
                goto out;

        qp->q.flags |= INET_FRAG_DROP;
        inet_frag_kill(&qp->q, &refs);

        /* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
        if (READ_ONCE(qp->q.fqdir->dead)) {
                inet_frag_queue_flush(&qp->q, 0);
                goto out;
        }

        __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
        __IP_INC_STATS(net, IPSTATS_MIB_REASMTIMEOUT);

        if (!(qp->q.flags & INET_FRAG_FIRST_IN))
                goto out;

        /* sk_buff::dev and sk_buff::rbnode are unionized. So we
         * pull the head out of the tree in order to be able to
         * deal with head->dev.
         */
        head = inet_frag_pull_head(&qp->q);
        if (!head)
                goto out;
        head->dev = dev_get_by_index_rcu(net, qp->iif);
        if (!head->dev)
                goto out;


        /* skb has no dst, perform route lookup again */
        iph = ip_hdr(head);
        reason = ip_route_input_noref(head, iph->daddr, iph->saddr,
                                      ip4h_dscp(iph), head->dev);
        if (reason)
                goto out;

        /* Only an end host needs to send an ICMP
         * "Fragment Reassembly Timeout" message, per RFC792.
         */
        reason = SKB_DROP_REASON_FRAG_REASM_TIMEOUT;
        if (frag_expire_skip_icmp(qp->q.key.v4.user) &&
            (skb_rtable(head)->rt_type != RTN_LOCAL))
                goto out;

        spin_unlock(&qp->q.lock);
        icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
        goto out_rcu_unlock;

out:
        spin_unlock(&qp->q.lock);
out_rcu_unlock:
        rcu_read_unlock();
        kfree_skb_reason(head, reason);
        inet_frag_putn(&qp->q, refs);
}

/* Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and create new one, if nothing is found.
 */
static struct ipq *ip_find(struct net *net, struct iphdr *iph,
                           u32 user, int vif)
{
        struct frag_v4_compare_key key = {
                .saddr = iph->saddr,
                .daddr = iph->daddr,
                .user = user,
                .vif = vif,
                .id = iph->id,
                .protocol = iph->protocol,
        };
        struct inet_frag_queue *q;

        q = inet_frag_find(net->ipv4.fqdir, &key);
        if (!q)
                return NULL;

        return container_of(q, struct ipq, q);
}

/* Is the fragment too far ahead to be part of ipq? */
static int ip_frag_too_far(struct ipq *qp)
{
        struct inet_peer *peer = qp->peer;
        unsigned int max = qp->q.fqdir->max_dist;
        unsigned int start, end;

        int rc;

        if (!peer || !max)
                return 0;

        start = qp->rid;
        end = atomic_inc_return(&peer->rid);
        qp->rid = end;

        rc = qp->q.fragments_tail && (end - start) > max;

        if (rc)
                __IP_INC_STATS(qp->q.fqdir->net, IPSTATS_MIB_REASMFAILS);

        return rc;
}

static int ip_frag_reinit(struct ipq *qp)
{
        if (!mod_timer_pending(&qp->q.timer, jiffies + qp->q.fqdir->timeout))
                return -ETIMEDOUT;

        inet_frag_queue_flush(&qp->q, SKB_DROP_REASON_FRAG_TOO_FAR);

        qp->q.flags = 0;
        qp->q.len = 0;
        qp->q.meat = 0;
        qp->iif = 0;
        qp->ecn = 0;

        return 0;
}

/* Add new segment to existing queue. */
static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb, int *refs)
{
        struct net *net = qp->q.fqdir->net;
        int ihl, end, flags, offset;
        struct sk_buff *prev_tail;
        struct net_device *dev;
        unsigned int fragsize;
        int err = -ENOENT;
        SKB_DR(reason);
        u8 ecn;

        /* If reassembly is already done, @skb must be a duplicate frag. */
        if (qp->q.flags & INET_FRAG_COMPLETE) {
                SKB_DR_SET(reason, DUP_FRAG);
                goto err;
        }

        if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
            unlikely(ip_frag_too_far(qp)) &&
            unlikely(err = ip_frag_reinit(qp))) {
                inet_frag_kill(&qp->q, refs);
                goto err;
        }

        ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
        offset = ntohs(ip_hdr(skb)->frag_off);
        flags = offset & ~IP_OFFSET;
        offset &= IP_OFFSET;
        offset <<= 3;           /* offset is in 8-byte chunks */
        ihl = ip_hdrlen(skb);

        /* Determine the position of this fragment. */
        end = offset + skb->len - skb_network_offset(skb) - ihl;
        err = -EINVAL;

        /* 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 corrupted.
                 */
                if (end < qp->q.len ||
                    ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len))
                        goto discard_qp;
                qp->q.flags |= INET_FRAG_LAST_IN;
                qp->q.len = end;
        } else {
                if (end&7) {
                        end &= ~7;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
                if (end > qp->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (qp->q.flags & INET_FRAG_LAST_IN)
                                goto discard_qp;
                        qp->q.len = end;
                }
        }
        if (end == offset)
                goto discard_qp;

        err = -ENOMEM;
        if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
                goto discard_qp;

        err = pskb_trim_rcsum(skb, end - offset);
        if (err)
                goto discard_qp;

        /* Note : skb->rbnode and skb->dev share the same location. */
        dev = skb->dev;
        /* Makes sure compiler wont do silly aliasing games */
        barrier();

        prev_tail = qp->q.fragments_tail;
        err = inet_frag_queue_insert(&qp->q, skb, offset, end);
        if (err)
                goto insert_error;

        if (dev)
                qp->iif = dev->ifindex;

        qp->q.stamp = skb->tstamp;
        qp->q.tstamp_type = skb->tstamp_type;
        qp->q.meat += skb->len;
        qp->ecn |= ecn;
        add_frag_mem_limit(qp->q.fqdir, skb->truesize);
        if (offset == 0)
                qp->q.flags |= INET_FRAG_FIRST_IN;

        fragsize = skb->len + ihl;

        if (fragsize > qp->q.max_size)
                qp->q.max_size = fragsize;

        if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
            fragsize > qp->max_df_size)
                qp->max_df_size = fragsize;

        if (qp->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            qp->q.meat == qp->q.len) {
                unsigned long orefdst = skb->_skb_refdst;

                skb->_skb_refdst = 0UL;
                err = ip_frag_reasm(qp, skb, prev_tail, dev, refs);
                skb->_skb_refdst = orefdst;
                if (err)
                        inet_frag_kill(&qp->q, refs);
                return err;
        }

        skb_dst_drop(skb);
        skb_orphan(skb);
        return -EINPROGRESS;

insert_error:
        if (err == IPFRAG_DUP) {
                SKB_DR_SET(reason, DUP_FRAG);
                err = -EINVAL;
                goto err;
        }
        err = -EINVAL;
        __IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
discard_qp:
        inet_frag_kill(&qp->q, refs);
        __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
err:
        kfree_skb_reason(skb, reason);
        return err;
}

static bool ip_frag_coalesce_ok(const struct ipq *qp)
{
        return qp->q.key.v4.user == IP_DEFRAG_LOCAL_DELIVER;
}

/* Build a new IP datagram from all its fragments. */
static int ip_frag_reasm(struct ipq *qp, struct sk_buff *skb,
                         struct sk_buff *prev_tail, struct net_device *dev,
                         int *refs)
{
        struct net *net = qp->q.fqdir->net;
        struct iphdr *iph;
        void *reasm_data;
        int len, err;
        u8 ecn;

        inet_frag_kill(&qp->q, refs);

        ecn = ip_frag_ecn_table[qp->ecn];
        if (unlikely(ecn == 0xff)) {
                err = -EINVAL;
                goto out_fail;
        }

        /* Make the one we just received the head. */
        reasm_data = inet_frag_reasm_prepare(&qp->q, skb, prev_tail);
        if (!reasm_data)
                goto out_nomem;

        len = ip_hdrlen(skb) + qp->q.len;
        err = -E2BIG;
        if (len > 65535)
                goto out_oversize;

        inet_frag_reasm_finish(&qp->q, skb, reasm_data,
                               ip_frag_coalesce_ok(qp));

        skb->dev = dev;
        IPCB(skb)->frag_max_size = max(qp->max_df_size, qp->q.max_size);

        iph = ip_hdr(skb);
        iph->tot_len = htons(len);
        iph->tos |= ecn;

        /* When we set IP_DF on a refragmented skb we must also force a
         * call to ip_fragment to avoid forwarding a DF-skb of size s while
         * original sender only sent fragments of size f (where f < s).
         *
         * We only set DF/IPSKB_FRAG_PMTU if such DF fragment was the largest
         * frag seen to avoid sending tiny DF-fragments in case skb was built
         * from one very small df-fragment and one large non-df frag.
         */
        if (qp->max_df_size == qp->q.max_size) {
                IPCB(skb)->flags |= IPSKB_FRAG_PMTU;
                iph->frag_off = htons(IP_DF);
        } else {
                iph->frag_off = 0;
        }

        ip_send_check(iph);

        __IP_INC_STATS(net, IPSTATS_MIB_REASMOKS);
        qp->q.rb_fragments = RB_ROOT;
        qp->q.fragments_tail = NULL;
        qp->q.last_run_head = NULL;
        return 0;

out_nomem:
        net_dbg_ratelimited("queue_glue: no memory for gluing queue %p\n", qp);
        err = -ENOMEM;
        goto out_fail;
out_oversize:
        net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->q.key.v4.saddr);
out_fail:
        __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
        return err;
}

/* Process an incoming IP datagram fragment. */
int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
{
        struct net_device *dev;
        struct ipq *qp;
        int vif;

        __IP_INC_STATS(net, IPSTATS_MIB_REASMREQDS);

        /* Lookup (or create) queue header */
        rcu_read_lock();
        dev = skb->dev ? : skb_dst_dev_rcu(skb);
        vif = l3mdev_master_ifindex_rcu(dev);
        qp = ip_find(net, ip_hdr(skb), user, vif);
        if (qp) {
                int ret, refs = 0;

                spin_lock(&qp->q.lock);

                ret = ip_frag_queue(qp, skb, &refs);

                spin_unlock(&qp->q.lock);
                rcu_read_unlock();
                inet_frag_putn(&qp->q, refs);
                return ret;
        }
        rcu_read_unlock();

        __IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -ENOMEM;
}
EXPORT_SYMBOL(ip_defrag);

struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
{
        struct iphdr iph;
        int netoff;
        u32 len;

        if (skb->protocol != htons(ETH_P_IP))
                return skb;

        netoff = skb_network_offset(skb);

        if (skb_copy_bits(skb, netoff, &iph, sizeof(iph)) < 0)
                return skb;

        if (iph.ihl < 5 || iph.version != 4)
                return skb;

        len = ntohs(iph.tot_len);
        if (skb->len < netoff + len || len < (iph.ihl * 4))
                return skb;

        if (ip_is_fragment(&iph)) {
                skb = skb_share_check(skb, GFP_ATOMIC);
                if (skb) {
                        if (!pskb_may_pull(skb, netoff + iph.ihl * 4)) {
                                kfree_skb(skb);
                                return NULL;
                        }
                        if (pskb_trim_rcsum(skb, netoff + len)) {
                                kfree_skb(skb);
                                return NULL;
                        }
                        memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
                        if (ip_defrag(net, skb, user))
                                return NULL;
                        skb_clear_hash(skb);
                }
        }
        return skb;
}
EXPORT_SYMBOL(ip_check_defrag);

#ifdef CONFIG_SYSCTL
static int dist_min;

static struct ctl_table ip4_frags_ns_ctl_table[] = {
        {
                .procname       = "ipfrag_high_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "ipfrag_low_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "ipfrag_time",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        {
                .procname       = "ipfrag_max_dist",
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &dist_min,
        },
};

/* secret interval has been deprecated */
static int ip4_frags_secret_interval_unused;
static struct ctl_table ip4_frags_ctl_table[] = {
        {
                .procname       = "ipfrag_secret_interval",
                .data           = &ip4_frags_secret_interval_unused,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
};

static int __net_init ip4_frags_ns_ctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;

        table = ip4_frags_ns_ctl_table;
        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
                if (!table)
                        goto err_alloc;

        }
        table[0].data   = &net->ipv4.fqdir->high_thresh;
        table[0].extra1 = &net->ipv4.fqdir->low_thresh;
        table[1].data   = &net->ipv4.fqdir->low_thresh;
        table[1].extra2 = &net->ipv4.fqdir->high_thresh;
        table[2].data   = &net->ipv4.fqdir->timeout;
        table[3].data   = &net->ipv4.fqdir->max_dist;

        hdr = register_net_sysctl_sz(net, "net/ipv4", table,
                                     ARRAY_SIZE(ip4_frags_ns_ctl_table));
        if (!hdr)
                goto err_reg;

        net->ipv4.frags_hdr = hdr;
        return 0;

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

static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
{
        const struct ctl_table *table;

        table = net->ipv4.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(net->ipv4.frags_hdr);
        kfree(table);
}

static void __init ip4_frags_ctl_register(void)
{
        register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
}
#else
static int ip4_frags_ns_ctl_register(struct net *net)
{
        return 0;
}

static void ip4_frags_ns_ctl_unregister(struct net *net)
{
}

static void __init ip4_frags_ctl_register(void)
{
}
#endif

static int __net_init ipv4_frags_init_net(struct net *net)
{
        int res;

        res = fqdir_init(&net->ipv4.fqdir, &ip4_frags, net);
        if (res < 0)
                return res;
        /* Fragment cache limits.
         *
         * The fragment memory accounting code, (tries to) account for
         * the real memory usage, by measuring both the size of frag
         * queue struct (inet_frag_queue (ipv4:ipq/ipv6:frag_queue))
         * and the SKB's truesize.
         *
         * A 64K fragment consumes 129736 bytes (44*2944)+200
         * (1500 truesize == 2944, sizeof(struct ipq) == 200)
         *
         * We will commit 4MB at one time. Should we cross that limit
         * we will prune down to 3MB, making room for approx 8 big 64K
         * fragments 8x128k.
         */
        net->ipv4.fqdir->high_thresh = 4 * 1024 * 1024;
        net->ipv4.fqdir->low_thresh  = 3 * 1024 * 1024;
        /*
         * Important NOTE! Fragment queue must be destroyed before MSL expires.
         * RFC791 is wrong proposing to prolongate timer each fragment arrival
         * by TTL.
         */
        net->ipv4.fqdir->timeout = IP_FRAG_TIME;

        net->ipv4.fqdir->max_dist = 64;

        res = ip4_frags_ns_ctl_register(net);
        if (res < 0)
                fqdir_exit(net->ipv4.fqdir);
        return res;
}

static void __net_exit ipv4_frags_pre_exit_net(struct net *net)
{
        fqdir_pre_exit(net->ipv4.fqdir);
}

static void __net_exit ipv4_frags_exit_net(struct net *net)
{
        ip4_frags_ns_ctl_unregister(net);
        fqdir_exit(net->ipv4.fqdir);
}

static struct pernet_operations ip4_frags_ops = {
        .init           = ipv4_frags_init_net,
        .pre_exit       = ipv4_frags_pre_exit_net,
        .exit           = ipv4_frags_exit_net,
};


static u32 ip4_key_hashfn(const void *data, u32 len, u32 seed)
{
        return jhash2(data,
                      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
}

static u32 ip4_obj_hashfn(const void *data, u32 len, u32 seed)
{
        const struct inet_frag_queue *fq = data;

        return jhash2((const u32 *)&fq->key.v4,
                      sizeof(struct frag_v4_compare_key) / sizeof(u32), seed);
}

static int ip4_obj_cmpfn(struct rhashtable_compare_arg *arg, const void *ptr)
{
        const struct frag_v4_compare_key *key = arg->key;
        const struct inet_frag_queue *fq = ptr;

        return !!memcmp(&fq->key, key, sizeof(*key));
}

static const struct rhashtable_params ip4_rhash_params = {
        .head_offset            = offsetof(struct inet_frag_queue, node),
        .key_offset             = offsetof(struct inet_frag_queue, key),
        .key_len                = sizeof(struct frag_v4_compare_key),
        .hashfn                 = ip4_key_hashfn,
        .obj_hashfn             = ip4_obj_hashfn,
        .obj_cmpfn              = ip4_obj_cmpfn,
        .automatic_shrinking    = true,
};

void __init ipfrag_init(void)
{
        ip4_frags.constructor = ip4_frag_init;
        ip4_frags.destructor = ip4_frag_free;
        ip4_frags.qsize = sizeof(struct ipq);
        ip4_frags.frag_expire = ip_expire;
        ip4_frags.frags_cache_name = ip_frag_cache_name;
        ip4_frags.rhash_params = ip4_rhash_params;
        if (inet_frags_init(&ip4_frags))
                panic("IP: failed to allocate ip4_frags cache\n");
        ip4_frags_ctl_register();
        register_pernet_subsys(&ip4_frags_ops);
}