ematch.c

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/*
 * net/sched/ematch.c       Extended Match API
 *
 *      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.
 *
 * Authors: Thomas Graf <[email protected]>
 *
 * ==========================================================================
 *
 * An extended match (ematch) is a small classification tool not worth
 * writing a full classifier for. Ematches can be interconnected to form
 * a logic expression and get attached to classifiers to extend their
 * functionatlity.
 *
 * The userspace part transforms the logic expressions into an array
 * consisting of multiple sequences of interconnected ematches separated
 * by markers. Precedence is implemented by a special ematch kind
 * referencing a sequence beyond the marker of the current sequence
 * causing the current position in the sequence to be pushed onto a stack
 * to allow the current position to be overwritten by the position referenced
 * in the special ematch. Matching continues in the new sequence until a
 * marker is reached causing the position to be restored from the stack.
 *
 * Example:
 *          A AND (B1 OR B2) AND C AND D
 *
 *              ------->-PUSH-------
 *    -->--    /         -->--      \   -->--
 *   /     \  /         /     \      \ /     \
 * +-------+-------+-------+-------+-------+--------+
 * | A AND | B AND | C AND | D END | B1 OR | B2 END |
 * +-------+-------+-------+-------+-------+--------+
 *                    \                      /
 *                     --------<-POP---------
 *
 * where B is a virtual ematch referencing to sequence starting with B1.
 *
 * ==========================================================================
 *
 * How to write an ematch in 60 seconds
 * ------------------------------------
 *
 *   1) Provide a matcher function:
 *      static int my_match(struct sk_buff *skb, struct tcf_ematch *m,
 *                          struct tcf_pkt_info *info)
 *      {
 *          struct mydata *d = (struct mydata *) m->data;
 *
 *          if (...matching goes here...)
 *              return 1;
 *          else
 *              return 0;
 *      }
 *
 *   2) Fill out a struct tcf_ematch_ops:
 *      static struct tcf_ematch_ops my_ops = {
 *          .kind = unique id,
 *          .datalen = sizeof(struct mydata),
 *          .match = my_match,
 *          .owner = THIS_MODULE,
 *      };
 *
 *   3) Register/Unregister your ematch:
 *      static int __init init_my_ematch(void)
 *      {
 *          return tcf_em_register(&my_ops);
 *      }
 *
 *      static void __exit exit_my_ematch(void)
 *      {
 *          tcf_em_unregister(&my_ops);
 *      }
 *
 *      module_init(init_my_ematch);
 *      module_exit(exit_my_ematch);
 *
 *   4) By now you should have two more seconds left, barely enough to
 *      open up a beer to watch the compilation going.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/rtnetlink.h>
#include <linux/skbuff.h>
#include <net/pkt_cls.h>

static LIST_HEAD(ematch_ops);
static DEFINE_RWLOCK(ematch_mod_lock);

static struct tcf_ematch_ops *tcf_em_lookup(u16 kind)
{
    struct tcf_ematch_ops *e = NULL;

    read_lock(&ematch_mod_lock);
    list_for_each_entry(e, &ematch_ops, link) {
        if (kind == e->kind) {
            if (!try_module_get(e->owner))
                e = NULL;
            read_unlock(&ematch_mod_lock);
            return e;
        }
    }
    read_unlock(&ematch_mod_lock);

    return NULL;
}

int tcf_em_register(struct tcf_ematch_ops *ops)
{
    int err = -EEXIST;
    struct tcf_ematch_ops *e;

    if (ops->match == NULL)
        return -EINVAL;

    write_lock(&ematch_mod_lock);
    list_for_each_entry(e, &ematch_ops, link)
        if (ops->kind == e->kind)
            goto errout;

    list_add_tail(&ops->link, &ematch_ops);
    err = 0;
errout:
    write_unlock(&ematch_mod_lock);
    return err;
}
EXPORT_SYMBOL(tcf_em_register);

void tcf_em_unregister(struct tcf_ematch_ops *ops)
{
    write_lock(&ematch_mod_lock);
    list_del(&ops->link);
    write_unlock(&ematch_mod_lock);
}
EXPORT_SYMBOL(tcf_em_unregister);

static inline struct tcf_ematch *tcf_em_get_match(struct tcf_ematch_tree *tree,
                          int index)
{
    return &tree->matches[index];
}


static int tcf_em_validate(struct tcf_proto *tp,
               struct tcf_ematch_tree_hdr *tree_hdr,
               struct tcf_ematch *em, struct nlattr *nla, int idx)
{
    int err = -EINVAL;
    struct tcf_ematch_hdr *em_hdr = nla_data(nla);
    int data_len = nla_len(nla) - sizeof(*em_hdr);
    void *data = (void *) em_hdr + sizeof(*em_hdr);

    if (!TCF_EM_REL_VALID(em_hdr->flags))
        goto errout;

    if (em_hdr->kind == TCF_EM_CONTAINER) {
        /* Special ematch called "container", carries an index
         * referencing an external ematch sequence.
         */
        u32 ref;

        if (data_len < sizeof(ref))
            goto errout;
        ref = *(u32 *) data;

        if (ref >= tree_hdr->nmatches)
            goto errout;

        /* We do not allow backward jumps to avoid loops and jumps
         * to our own position are of course illegal.
         */
        if (ref <= idx)
            goto errout;


        em->data = ref;
    } else {
        /* Note: This lookup will increase the module refcnt
         * of the ematch module referenced. In case of a failure,
         * a destroy function is called by the underlying layer
         * which automatically releases the reference again, therefore
         * the module MUST not be given back under any circumstances
         * here. Be aware, the destroy function assumes that the
         * module is held if the ops field is non zero.
         */
        em->ops = tcf_em_lookup(em_hdr->kind);

        if (em->ops == NULL) {
            err = -ENOENT;
#ifdef CONFIG_MODULES
            __rtnl_unlock();
            request_module("ematch-kind-%u", em_hdr->kind);
            rtnl_lock();
            em->ops = tcf_em_lookup(em_hdr->kind);
            if (em->ops) {
                /* We dropped the RTNL mutex in order to
                 * perform the module load. Tell the caller
                 * to replay the request.
                 */
                module_put(em->ops->owner);
                err = -EAGAIN;
            }
#endif
            goto errout;
        }

        /* ematch module provides expected length of data, so we
         * can do a basic sanity check.
         */
        if (em->ops->datalen && data_len < em->ops->datalen)
            goto errout;

        if (em->ops->change) {
            err = em->ops->change(tp, data, data_len, em);
            if (err < 0)
                goto errout;
        } else if (data_len > 0) {
            /* ematch module doesn't provide an own change
             * procedure and expects us to allocate and copy
             * the ematch data.
             *
             * TCF_EM_SIMPLE may be specified stating that the
             * data only consists of a u32 integer and the module
             * does not expected a memory reference but rather
             * the value carried.
             */
            if (em_hdr->flags & TCF_EM_SIMPLE) {
                if (data_len < sizeof(u32))
                    goto errout;
                em->data = *(u32 *) data;
            } else {
                void *v = kmemdup(data, data_len, GFP_KERNEL);
                if (v == NULL) {
                    err = -ENOBUFS;
                    goto errout;
                }
                em->data = (unsigned long) v;
            }
        }
    }

    em->matchid = em_hdr->matchid;
    em->flags = em_hdr->flags;
    em->datalen = data_len;

    err = 0;
errout:
    return err;
}

static const struct nla_policy em_policy[TCA_EMATCH_TREE_MAX + 1] = {
    [TCA_EMATCH_TREE_HDR]   = { .len = sizeof(struct tcf_ematch_tree_hdr) },
    [TCA_EMATCH_TREE_LIST]  = { .type = NLA_NESTED },
};

int tcf_em_tree_validate(struct tcf_proto *tp, struct nlattr *nla,
             struct tcf_ematch_tree *tree)
{
    int idx, list_len, matches_len, err;
    struct nlattr *tb[TCA_EMATCH_TREE_MAX + 1];
    struct nlattr *rt_match, *rt_hdr, *rt_list;
    struct tcf_ematch_tree_hdr *tree_hdr;
    struct tcf_ematch *em;

    memset(tree, 0, sizeof(*tree));
    if (!nla)
        return 0;

    err = nla_parse_nested(tb, TCA_EMATCH_TREE_MAX, nla, em_policy);
    if (err < 0)
        goto errout;

    err = -EINVAL;
    rt_hdr = tb[TCA_EMATCH_TREE_HDR];
    rt_list = tb[TCA_EMATCH_TREE_LIST];

    if (rt_hdr == NULL || rt_list == NULL)
        goto errout;

    tree_hdr = nla_data(rt_hdr);
    memcpy(&tree->hdr, tree_hdr, sizeof(*tree_hdr));

    rt_match = nla_data(rt_list);
    list_len = nla_len(rt_list);
    matches_len = tree_hdr->nmatches * sizeof(*em);

    tree->matches = kzalloc(matches_len, GFP_KERNEL);
    if (tree->matches == NULL)
        goto errout;

    /* We do not use nla_parse_nested here because the maximum
     * number of attributes is unknown. This saves us the allocation
     * for a tb buffer which would serve no purpose at all.
     *
     * The array of rt attributes is parsed in the order as they are
     * provided, their type must be incremental from 1 to n. Even
     * if it does not serve any real purpose, a failure of sticking
     * to this policy will result in parsing failure.
     */
    for (idx = 0; nla_ok(rt_match, list_len); idx++) {
        err = -EINVAL;

        if (rt_match->nla_type != (idx + 1))
            goto errout_abort;

        if (idx >= tree_hdr->nmatches)
            goto errout_abort;

        if (nla_len(rt_match) < sizeof(struct tcf_ematch_hdr))
            goto errout_abort;

        em = tcf_em_get_match(tree, idx);

        err = tcf_em_validate(tp, tree_hdr, em, rt_match, idx);
        if (err < 0)
            goto errout_abort;

        rt_match = nla_next(rt_match, &list_len);
    }

    /* Check if the number of matches provided by userspace actually
     * complies with the array of matches. The number was used for
     * the validation of references and a mismatch could lead to
     * undefined references during the matching process.
     */
    if (idx != tree_hdr->nmatches) {
        err = -EINVAL;
        goto errout_abort;
    }

    err = 0;
errout:
    return err;

errout_abort:
    tcf_em_tree_destroy(tp, tree);
    return err;
}
EXPORT_SYMBOL(tcf_em_tree_validate);

void tcf_em_tree_destroy(struct tcf_proto *tp, struct tcf_ematch_tree *tree)
{
    int i;

    if (tree->matches == NULL)
        return;

    for (i = 0; i < tree->hdr.nmatches; i++) {
        struct tcf_ematch *em = tcf_em_get_match(tree, i);

        if (em->ops) {
            if (em->ops->destroy)
                em->ops->destroy(tp, em);
            else if (!tcf_em_is_simple(em))
                kfree((void *) em->data);
            module_put(em->ops->owner);
        }
    }

    tree->hdr.nmatches = 0;
    kfree(tree->matches);
    tree->matches = NULL;
}
EXPORT_SYMBOL(tcf_em_tree_destroy);

int tcf_em_tree_dump(struct sk_buff *skb, struct tcf_ematch_tree *tree, int tlv)
{
    int i;
    u8 *tail;
    struct nlattr *top_start;
    struct nlattr *list_start;

    top_start = nla_nest_start(skb, tlv);
    if (top_start == NULL)
        goto nla_put_failure;

    if (nla_put(skb, TCA_EMATCH_TREE_HDR, sizeof(tree->hdr), &tree->hdr))
        goto nla_put_failure;

    list_start = nla_nest_start(skb, TCA_EMATCH_TREE_LIST);
    if (list_start == NULL)
        goto nla_put_failure;

    tail = skb_tail_pointer(skb);
    for (i = 0; i < tree->hdr.nmatches; i++) {
        struct nlattr *match_start = (struct nlattr *)tail;
        struct tcf_ematch *em = tcf_em_get_match(tree, i);
        struct tcf_ematch_hdr em_hdr = {
            .kind = em->ops ? em->ops->kind : TCF_EM_CONTAINER,
            .matchid = em->matchid,
            .flags = em->flags
        };

        if (nla_put(skb, i + 1, sizeof(em_hdr), &em_hdr))
            goto nla_put_failure;

        if (em->ops && em->ops->dump) {
            if (em->ops->dump(skb, em) < 0)
                goto nla_put_failure;
        } else if (tcf_em_is_container(em) || tcf_em_is_simple(em)) {
            u32 u = em->data;
            nla_put_nohdr(skb, sizeof(u), &u);
        } else if (em->datalen > 0)
            nla_put_nohdr(skb, em->datalen, (void *) em->data);

        tail = skb_tail_pointer(skb);
        match_start->nla_len = tail - (u8 *)match_start;
    }

    nla_nest_end(skb, list_start);
    nla_nest_end(skb, top_start);

    return 0;

nla_put_failure:
    return -1;
}
EXPORT_SYMBOL(tcf_em_tree_dump);

static inline int tcf_em_match(struct sk_buff *skb, struct tcf_ematch *em,
                   struct tcf_pkt_info *info)
{
    int r = em->ops->match(skb, em, info);

    return tcf_em_is_inverted(em) ? !r : r;
}

/* Do not use this function directly, use tcf_em_tree_match instead */
int __tcf_em_tree_match(struct sk_buff *skb, struct tcf_ematch_tree *tree,
            struct tcf_pkt_info *info)
{
    int stackp = 0, match_idx = 0, res = 0;
    struct tcf_ematch *cur_match;
    int stack[CONFIG_NET_EMATCH_STACK];

proceed:
    while (match_idx < tree->hdr.nmatches) {
        cur_match = tcf_em_get_match(tree, match_idx);

        if (tcf_em_is_container(cur_match)) {
            if (unlikely(stackp >= CONFIG_NET_EMATCH_STACK))
                goto stack_overflow;

            stack[stackp++] = match_idx;
            match_idx = cur_match->data;
            goto proceed;
        }

        res = tcf_em_match(skb, cur_match, info);

        if (tcf_em_early_end(cur_match, res))
            break;

        match_idx++;
    }

pop_stack:
    if (stackp > 0) {
        match_idx = stack[--stackp];
        cur_match = tcf_em_get_match(tree, match_idx);

        if (tcf_em_early_end(cur_match, res))
            goto pop_stack;
        else {
            match_idx++;
            goto proceed;
        }
    }

    return res;

stack_overflow:
    net_warn_ratelimited("tc ematch: local stack overflow, increase NET_EMATCH_STACK\n");
    return -1;
}
EXPORT_SYMBOL(__tcf_em_tree_match);