xt_sctp.c

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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/sctp/sctp.h>
#include <linux/sctp.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_sctp.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Kiran Kumar Immidi");
MODULE_DESCRIPTION("Xtables: SCTP protocol packet match");
MODULE_ALIAS("ipt_sctp");
MODULE_ALIAS("ip6t_sctp");

#define SCCHECK(cond, option, flag, invflag) (!((flag) & (option)) \
                          || (!!((invflag) & (option)) ^ (cond)))

static bool
match_flags(const struct xt_sctp_flag_info *flag_info,
        const int flag_count,
        u_int8_t chunktype,
        u_int8_t chunkflags)
{
    int i;

    for (i = 0; i < flag_count; i++)
        if (flag_info[i].chunktype == chunktype)
            return (chunkflags & flag_info[i].flag_mask) == flag_info[i].flag;

    return true;
}

static inline bool
match_packet(const struct sk_buff *skb,
         unsigned int offset,
         const struct xt_sctp_info *info,
         bool *hotdrop)
{
    u_int32_t chunkmapcopy[256 / sizeof (u_int32_t)];
    const sctp_chunkhdr_t *sch;
    sctp_chunkhdr_t _sch;
    int chunk_match_type = info->chunk_match_type;
    const struct xt_sctp_flag_info *flag_info = info->flag_info;
    int flag_count = info->flag_count;

#ifdef DEBUG
    int i = 0;
#endif

    if (chunk_match_type == SCTP_CHUNK_MATCH_ALL)
        SCTP_CHUNKMAP_COPY(chunkmapcopy, info->chunkmap);

    do {
        sch = skb_header_pointer(skb, offset, sizeof(_sch), &_sch);
        if (sch == NULL || sch->length == 0) {
            pr_debug("Dropping invalid SCTP packet.\n");
            *hotdrop = true;
            return false;
        }
#ifdef DEBUG
        pr_debug("Chunk num: %d\toffset: %d\ttype: %d\tlength: %d"
             "\tflags: %x\n",
             ++i, offset, sch->type, htons(sch->length),
             sch->flags);
#endif
        offset += WORD_ROUND(ntohs(sch->length));

        pr_debug("skb->len: %d\toffset: %d\n", skb->len, offset);

        if (SCTP_CHUNKMAP_IS_SET(info->chunkmap, sch->type)) {
            switch (chunk_match_type) {
            case SCTP_CHUNK_MATCH_ANY:
                if (match_flags(flag_info, flag_count,
                    sch->type, sch->flags)) {
                    return true;
                }
                break;

            case SCTP_CHUNK_MATCH_ALL:
                if (match_flags(flag_info, flag_count,
                    sch->type, sch->flags))
                    SCTP_CHUNKMAP_CLEAR(chunkmapcopy, sch->type);
                break;

            case SCTP_CHUNK_MATCH_ONLY:
                if (!match_flags(flag_info, flag_count,
                    sch->type, sch->flags))
                    return false;
                break;
            }
        } else {
            switch (chunk_match_type) {
            case SCTP_CHUNK_MATCH_ONLY:
                return false;
            }
        }
    } while (offset < skb->len);

    switch (chunk_match_type) {
    case SCTP_CHUNK_MATCH_ALL:
        return SCTP_CHUNKMAP_IS_CLEAR(chunkmapcopy);
    case SCTP_CHUNK_MATCH_ANY:
        return false;
    case SCTP_CHUNK_MATCH_ONLY:
        return true;
    }

    /* This will never be reached, but required to stop compiler whine */
    return false;
}

static bool
sctp_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct xt_sctp_info *info = par->matchinfo;
    const sctp_sctphdr_t *sh;
    sctp_sctphdr_t _sh;

    if (par->fragoff != 0) {
        pr_debug("Dropping non-first fragment.. FIXME\n");
        return false;
    }

    sh = skb_header_pointer(skb, par->thoff, sizeof(_sh), &_sh);
    if (sh == NULL) {
        pr_debug("Dropping evil TCP offset=0 tinygram.\n");
        par->hotdrop = true;
        return false;
    }
    pr_debug("spt: %d\tdpt: %d\n", ntohs(sh->source), ntohs(sh->dest));

    return  SCCHECK(ntohs(sh->source) >= info->spts[0]
            && ntohs(sh->source) <= info->spts[1],
            XT_SCTP_SRC_PORTS, info->flags, info->invflags)
        && SCCHECK(ntohs(sh->dest) >= info->dpts[0]
            && ntohs(sh->dest) <= info->dpts[1],
            XT_SCTP_DEST_PORTS, info->flags, info->invflags)
        && SCCHECK(match_packet(skb, par->thoff + sizeof(sctp_sctphdr_t),
                    info, &par->hotdrop),
               XT_SCTP_CHUNK_TYPES, info->flags, info->invflags);
}

static int sctp_mt_check(const struct xt_mtchk_param *par)
{
    const struct xt_sctp_info *info = par->matchinfo;

    if (info->flags & ~XT_SCTP_VALID_FLAGS)
        return -EINVAL;
    if (info->invflags & ~XT_SCTP_VALID_FLAGS)
        return -EINVAL;
    if (info->invflags & ~info->flags)
        return -EINVAL;
    if (!(info->flags & XT_SCTP_CHUNK_TYPES))
        return 0;
    if (info->chunk_match_type & (SCTP_CHUNK_MATCH_ALL |
        SCTP_CHUNK_MATCH_ANY | SCTP_CHUNK_MATCH_ONLY))
        return 0;
    return -EINVAL;
}

static struct xt_match sctp_mt_reg[] __read_mostly = {
    {
        .name       = "sctp",
        .family     = NFPROTO_IPV4,
        .checkentry = sctp_mt_check,
        .match      = sctp_mt,
        .matchsize  = sizeof(struct xt_sctp_info),
        .proto      = IPPROTO_SCTP,
        .me     = THIS_MODULE
    },
    {
        .name       = "sctp",
        .family     = NFPROTO_IPV6,
        .checkentry = sctp_mt_check,
        .match      = sctp_mt,
        .matchsize  = sizeof(struct xt_sctp_info),
        .proto      = IPPROTO_SCTP,
        .me     = THIS_MODULE
    },
};

static int __init sctp_mt_init(void)
{
    return xt_register_matches(sctp_mt_reg, ARRAY_SIZE(sctp_mt_reg));
}

static void __exit sctp_mt_exit(void)
{
    xt_unregister_matches(sctp_mt_reg, ARRAY_SIZE(sctp_mt_reg));
}

module_init(sctp_mt_init);
module_exit(sctp_mt_exit);