root/net/netfilter/xt_sctp.c

DEFINITIONS

1. match_flags
2. match_packet
3. sctp_mt
4. sctp_mt_check
5. sctp_mt_init
6. sctp_mt_exit

#include <linux/module.h>
#include <linux/skbuff.h>
#include <net/ip.h>
#include <net/ipv6.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");

#ifdef DEBUG_SCTP
#define duprintf(format, args...) printk(format , ## args)
#else
#define duprintf(format, args...)
#endif

#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_SCTP
        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) {
                        duprintf("Dropping invalid SCTP packet.\n");
                        *hotdrop = true;
                        return false;
                }

                duprintf("Chunk num: %d\toffset: %d\ttype: %d\tlength: %d\tflags: %x\n",
                                ++i, offset, sch->type, htons(sch->length), sch->flags);

                offset += (ntohs(sch->length) + 3) & ~3;

                duprintf("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(info->chunkmap);
        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, const struct xt_match_param *par)
{
        const struct xt_sctp_info *info = par->matchinfo;
        const sctp_sctphdr_t *sh;
        sctp_sctphdr_t _sh;

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

        sh = skb_header_pointer(skb, par->thoff, sizeof(_sh), &_sh);
        if (sh == NULL) {
                duprintf("Dropping evil TCP offset=0 tinygram.\n");
                *par->hotdrop = true;
                return false;
        }
        duprintf("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 bool sctp_mt_check(const struct xt_mtchk_param *par)
{
        const struct xt_sctp_info *info = par->matchinfo;

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

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);