/*
 * Stream Parser
 *
 * Copyright (c) 2016 Tom Herbert <tom@herbertland.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation.
 */

#include <linux/bpf.h>
#include <linux/errno.h>
#include <linux/errqueue.h>
#include <linux/file.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/rculist.h>
#include <linux/skbuff.h>
#include <linux/socket.h>
#include <linux/uaccess.h>
#include <linux/workqueue.h>
#include <net/strparser.h>
#include <net/netns/generic.h>
#include <net/sock.h>

static struct workqueue_struct *strp_wq;

struct _strp_msg {
        /* Internal cb structure. struct strp_msg must be first for passing
         * to upper layer.
         */
        struct strp_msg strp;
        int accum_len;
        int early_eaten;
};

static inline struct _strp_msg *_strp_msg(struct sk_buff *skb)
{
        return (struct _strp_msg *)((void *)skb->cb +
                offsetof(struct qdisc_skb_cb, data));
}

/* Lower lock held */
static void strp_abort_strp(struct strparser *strp, int err)
{
        /* Unrecoverable error in receive */

        cancel_delayed_work(&strp->msg_timer_work);

        if (strp->stopped)
                return;

        strp->stopped = 1;

        if (strp->sk) {
                struct sock *sk = strp->sk;

                /* Report an error on the lower socket */
                sk->sk_err = err;
                sk->sk_error_report(sk);
        }
}

static void strp_start_timer(struct strparser *strp, long timeo)
{
        if (timeo)
                mod_delayed_work(strp_wq, &strp->msg_timer_work, timeo);
}

/* Lower lock held */
static void strp_parser_err(struct strparser *strp, int err,
                            read_descriptor_t *desc)
{
        desc->error = err;
        kfree_skb(strp->skb_head);
        strp->skb_head = NULL;
        strp->cb.abort_parser(strp, err);
}

static inline int strp_peek_len(struct strparser *strp)
{
        if (strp->sk) {
                struct socket *sock = strp->sk->sk_socket;

                return sock->ops->peek_len(sock);
        }

        /* If we don't have an associated socket there's nothing to peek.
         * Return int max to avoid stopping the strparser.
         */

        return INT_MAX;
}

/* Lower socket lock held */
static int __strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
                       unsigned int orig_offset, size_t orig_len,
                       size_t max_msg_size, long timeo)
{
        struct strparser *strp = (struct strparser *)desc->arg.data;
        struct _strp_msg *stm;
        struct sk_buff *head, *skb;
        size_t eaten = 0, cand_len;
        ssize_t extra;
        int err;
        bool cloned_orig = false;

        if (strp->paused)
                return 0;

        head = strp->skb_head;
        if (head) {
                /* Message already in progress */

                stm = _strp_msg(head);
                if (unlikely(stm->early_eaten)) {
                        /* Already some number of bytes on the receive sock
                         * data saved in skb_head, just indicate they
                         * are consumed.
                         */
                        eaten = orig_len <= stm->early_eaten ?
                                orig_len : stm->early_eaten;
                        stm->early_eaten -= eaten;

                        return eaten;
                }

                if (unlikely(orig_offset)) {
                        /* Getting data with a non-zero offset when a message is
                         * in progress is not expected. If it does happen, we
                         * need to clone and pull since we can't deal with
                         * offsets in the skbs for a message expect in the head.
                         */
                        orig_skb = skb_clone(orig_skb, GFP_ATOMIC);
                        if (!orig_skb) {
                                STRP_STATS_INCR(strp->stats.mem_fail);
                                desc->error = -ENOMEM;
                                return 0;
                        }
                        if (!pskb_pull(orig_skb, orig_offset)) {
                                STRP_STATS_INCR(strp->stats.mem_fail);
                                kfree_skb(orig_skb);
                                desc->error = -ENOMEM;
                                return 0;
                        }
                        cloned_orig = true;
                        orig_offset = 0;
                }

                if (!strp->skb_nextp) {
                        /* We are going to append to the frags_list of head.
                         * Need to unshare the frag_list.
                         */
                        err = skb_unclone(head, GFP_ATOMIC);
                        if (err) {
                                STRP_STATS_INCR(strp->stats.mem_fail);
                                desc->error = err;
                                return 0;
                        }

                        if (unlikely(skb_shinfo(head)->frag_list)) {
                                /* We can't append to an sk_buff that already
                                 * has a frag_list. We create a new head, point
                                 * the frag_list of that to the old head, and
                                 * then are able to use the old head->next for
                                 * appending to the message.
                                 */
                                if (WARN_ON(head->next)) {
                                        desc->error = -EINVAL;
                                        return 0;
                                }

                                skb = alloc_skb(0, GFP_ATOMIC);
                                if (!skb) {
                                        STRP_STATS_INCR(strp->stats.mem_fail);
                                        desc->error = -ENOMEM;
                                        return 0;
                                }
                                skb->len = head->len;
                                skb->data_len = head->len;
                                skb->truesize = head->truesize;
                                *_strp_msg(skb) = *_strp_msg(head);
                                strp->skb_nextp = &head->next;
                                skb_shinfo(skb)->frag_list = head;
                                strp->skb_head = skb;
                                head = skb;
                        } else {
                                strp->skb_nextp =
                                    &skb_shinfo(head)->frag_list;
                        }
                }
        }

        while (eaten < orig_len) {
                /* Always clone since we will consume something */
                skb = skb_clone(orig_skb, GFP_ATOMIC);
                if (!skb) {
                        STRP_STATS_INCR(strp->stats.mem_fail);
                        desc->error = -ENOMEM;
                        break;
                }

                cand_len = orig_len - eaten;

                head = strp->skb_head;
                if (!head) {
                        head = skb;
                        strp->skb_head = head;
                        /* Will set skb_nextp on next packet if needed */
                        strp->skb_nextp = NULL;
                        stm = _strp_msg(head);
                        memset(stm, 0, sizeof(*stm));
                        stm->strp.offset = orig_offset + eaten;
                } else {
                        /* Unclone since we may be appending to an skb that we
                         * already share a frag_list with.
                         */
                        err = skb_unclone(skb, GFP_ATOMIC);
                        if (err) {
                                STRP_STATS_INCR(strp->stats.mem_fail);
                                desc->error = err;
                                break;
                        }

                        stm = _strp_msg(head);
                        *strp->skb_nextp = skb;
                        strp->skb_nextp = &skb->next;
                        head->data_len += skb->len;
                        head->len += skb->len;
                        head->truesize += skb->truesize;
                }

                if (!stm->strp.full_len) {
                        ssize_t len;

                        len = (*strp->cb.parse_msg)(strp, head);

                        if (!len) {
                                /* Need more header to determine length */
                                if (!stm->accum_len) {
                                        /* Start RX timer for new message */
                                        strp_start_timer(strp, timeo);
                                }
                                stm->accum_len += cand_len;
                                eaten += cand_len;
                                STRP_STATS_INCR(strp->stats.need_more_hdr);
                                WARN_ON(eaten != orig_len);
                                break;
                        } else if (len < 0) {
                                if (len == -ESTRPIPE && stm->accum_len) {
                                        len = -ENODATA;
                                        strp->unrecov_intr = 1;
                                } else {
                                        strp->interrupted = 1;
                                }
                                strp_parser_err(strp, len, desc);
                                break;
                        } else if (len > max_msg_size) {
                                /* Message length exceeds maximum allowed */
                                STRP_STATS_INCR(strp->stats.msg_too_big);
                                strp_parser_err(strp, -EMSGSIZE, desc);
                                break;
                        } else if (len <= (ssize_t)head->len -
                                          skb->len - stm->strp.offset) {
                                /* Length must be into new skb (and also
                                 * greater than zero)
                                 */
                                STRP_STATS_INCR(strp->stats.bad_hdr_len);
                                strp_parser_err(strp, -EPROTO, desc);
                                break;
                        }

                        stm->strp.full_len = len;
                }

                extra = (ssize_t)(stm->accum_len + cand_len) -
                        stm->strp.full_len;

                if (extra < 0) {
                        /* Message not complete yet. */
                        if (stm->strp.full_len - stm->accum_len >
                            strp_peek_len(strp)) {
                                /* Don't have the whole message in the socket
                                 * buffer. Set strp->need_bytes to wait for
                                 * the rest of the message. Also, set "early
                                 * eaten" since we've already buffered the skb
                                 * but don't consume yet per strp_read_sock.
                                 */

                                if (!stm->accum_len) {
                                        /* Start RX timer for new message */
                                        strp_start_timer(strp, timeo);
                                }

                                strp->need_bytes = stm->strp.full_len -
                                                       stm->accum_len;
                                stm->accum_len += cand_len;
                                stm->early_eaten = cand_len;
                                STRP_STATS_ADD(strp->stats.bytes, cand_len);
                                desc->count = 0; /* Stop reading socket */
                                break;
                        }
                        stm->accum_len += cand_len;
                        eaten += cand_len;
                        WARN_ON(eaten != orig_len);
                        break;
                }

                /* Positive extra indicates ore bytes than needed for the
                 * message
                 */

                WARN_ON(extra > cand_len);

                eaten += (cand_len - extra);

                /* Hurray, we have a new message! */
                cancel_delayed_work(&strp->msg_timer_work);
                strp->skb_head = NULL;
                STRP_STATS_INCR(strp->stats.msgs);

                /* Give skb to upper layer */
                strp->cb.rcv_msg(strp, head);

                if (unlikely(strp->paused)) {
                        /* Upper layer paused strp */
                        break;
                }
        }

        if (cloned_orig)
                kfree_skb(orig_skb);

        STRP_STATS_ADD(strp->stats.bytes, eaten);

        return eaten;
}

int strp_process(struct strparser *strp, struct sk_buff *orig_skb,
                 unsigned int orig_offset, size_t orig_len,
                 size_t max_msg_size, long timeo)
{
        read_descriptor_t desc; /* Dummy arg to strp_recv */

        desc.arg.data = strp;

        return __strp_recv(&desc, orig_skb, orig_offset, orig_len,
                           max_msg_size, timeo);
}
EXPORT_SYMBOL_GPL(strp_process);

static int strp_recv(read_descriptor_t *desc, struct sk_buff *orig_skb,
                     unsigned int orig_offset, size_t orig_len)
{
        struct strparser *strp = (struct strparser *)desc->arg.data;

        return __strp_recv(desc, orig_skb, orig_offset, orig_len,
                           strp->sk->sk_rcvbuf, strp->sk->sk_rcvtimeo);
}

static int default_read_sock_done(struct strparser *strp, int err)
{
        return err;
}

/* Called with lock held on lower socket */
static int strp_read_sock(struct strparser *strp)
{
        struct socket *sock = strp->sk->sk_socket;
        read_descriptor_t desc;

        if (unlikely(!sock || !sock->ops || !sock->ops->read_sock))
                return -EBUSY;

        desc.arg.data = strp;
        desc.error = 0;
        desc.count = 1; /* give more than one skb per call */

        /* sk should be locked here, so okay to do read_sock */
        sock->ops->read_sock(strp->sk, &desc, strp_recv);

        desc.error = strp->cb.read_sock_done(strp, desc.error);

        return desc.error;
}

/* Lower sock lock held */
void strp_data_ready(struct strparser *strp)
{
        if (unlikely(strp->stopped))
                return;

        /* This check is needed to synchronize with do_strp_work.
         * do_strp_work acquires a process lock (lock_sock) whereas
         * the lock held here is bh_lock_sock. The two locks can be
         * held by different threads at the same time, but bh_lock_sock
         * allows a thread in BH context to safely check if the process
         * lock is held. In this case, if the lock is held, queue work.
         */
        if (sock_owned_by_user(strp->sk)) {
                queue_work(strp_wq, &strp->work);
                return;
        }

        if (strp->paused)
                return;

        if (strp->need_bytes) {
                if (strp_peek_len(strp) >= strp->need_bytes)
                        strp->need_bytes = 0;
                else
                        return;
        }

        if (strp_read_sock(strp) == -ENOMEM)
                queue_work(strp_wq, &strp->work);
}
EXPORT_SYMBOL_GPL(strp_data_ready);

static void do_strp_work(struct strparser *strp)
{
        read_descriptor_t rd_desc;

        /* We need the read lock to synchronize with strp_data_ready. We
         * need the socket lock for calling strp_read_sock.
         */
        strp->cb.lock(strp);

        if (unlikely(strp->stopped))
                goto out;

        if (strp->paused)
                goto out;

        rd_desc.arg.data = strp;

        if (strp_read_sock(strp) == -ENOMEM)
                queue_work(strp_wq, &strp->work);

out:
        strp->cb.unlock(strp);
}

static void strp_work(struct work_struct *w)
{
        do_strp_work(container_of(w, struct strparser, work));
}

static void strp_msg_timeout(struct work_struct *w)
{
        struct strparser *strp = container_of(w, struct strparser,
                                              msg_timer_work.work);

        /* Message assembly timed out */
        STRP_STATS_INCR(strp->stats.msg_timeouts);
        strp->cb.lock(strp);
        strp->cb.abort_parser(strp, ETIMEDOUT);
        strp->cb.unlock(strp);
}

static void strp_sock_lock(struct strparser *strp)
{
        lock_sock(strp->sk);
}

static void strp_sock_unlock(struct strparser *strp)
{
        release_sock(strp->sk);
}

int strp_init(struct strparser *strp, struct sock *sk,
              const struct strp_callbacks *cb)
{

        if (!cb || !cb->rcv_msg || !cb->parse_msg)
                return -EINVAL;

        /* The sk (sock) arg determines the mode of the stream parser.
         *
         * If the sock is set then the strparser is in receive callback mode.
         * The upper layer calls strp_data_ready to kick receive processing
         * and strparser calls the read_sock function on the socket to
         * get packets.
         *
         * If the sock is not set then the strparser is in general mode.
         * The upper layer calls strp_process for each skb to be parsed.
         */

        if (!sk) {
                if (!cb->lock || !cb->unlock)
                        return -EINVAL;
        }

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

        strp->sk = sk;

        strp->cb.lock = cb->lock ? : strp_sock_lock;
        strp->cb.unlock = cb->unlock ? : strp_sock_unlock;
        strp->cb.rcv_msg = cb->rcv_msg;
        strp->cb.parse_msg = cb->parse_msg;
        strp->cb.read_sock_done = cb->read_sock_done ? : default_read_sock_done;
        strp->cb.abort_parser = cb->abort_parser ? : strp_abort_strp;

        INIT_DELAYED_WORK(&strp->msg_timer_work, strp_msg_timeout);
        INIT_WORK(&strp->work, strp_work);

        return 0;
}
EXPORT_SYMBOL_GPL(strp_init);

void strp_unpause(struct strparser *strp)
{
        strp->paused = 0;

        /* Sync setting paused with RX work */
        smp_mb();

        queue_work(strp_wq, &strp->work);
}
EXPORT_SYMBOL_GPL(strp_unpause);

/* strp must already be stopped so that strp_recv will no longer be called.
 * Note that strp_done is not called with the lower socket held.
 */
void strp_done(struct strparser *strp)
{
        WARN_ON(!strp->stopped);

        cancel_delayed_work_sync(&strp->msg_timer_work);
        cancel_work_sync(&strp->work);

        if (strp->skb_head) {
                kfree_skb(strp->skb_head);
                strp->skb_head = NULL;
        }
}
EXPORT_SYMBOL_GPL(strp_done);

void strp_stop(struct strparser *strp)
{
        strp->stopped = 1;
}
EXPORT_SYMBOL_GPL(strp_stop);

void strp_check_rcv(struct strparser *strp)
{
        queue_work(strp_wq, &strp->work);
}
EXPORT_SYMBOL_GPL(strp_check_rcv);

static int __init strp_mod_init(void)
{
        strp_wq = create_singlethread_workqueue("kstrp");

        return 0;
}

static void __exit strp_mod_exit(void)
{
        destroy_workqueue(strp_wq);
}
module_init(strp_mod_init);
module_exit(strp_mod_exit);
MODULE_LICENSE("GPL");