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[/] [or1k/] [trunk/] [linux/] [linux-2.4/] [net/] [ipv4/] [netfilter/] [ipt_tcpmss.c] - Blame information for rev 1765

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Line No. Rev Author Line
1 1275 phoenix 
/* Kernel module to match TCP MSS values. */
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <net/tcp.h>
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#include <linux/netfilter_ipv4/ipt_tcpmss.h>
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#include <linux/netfilter_ipv4/ip_tables.h>
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#define TH_SYN 0x02
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/* Returns 1 if the mss option is set and matched by the range, 0 otherwise */
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static inline int
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mssoption_match(u_int16_t min, u_int16_t max,
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                const struct tcphdr *tcp,
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                u_int16_t datalen,
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                int invert,
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                int *hotdrop)
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{
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        unsigned int i;
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        const u_int8_t *opt = (u_int8_t *)tcp;
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        /* If we don't have the whole header, drop packet. */
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        if (tcp->doff * 4 > datalen) {
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                *hotdrop = 1;
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                return 0;
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        }
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        for (i = sizeof(struct tcphdr); i < tcp->doff * 4; ) {
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                if ((opt[i] == TCPOPT_MSS)
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                    && ((tcp->doff * 4 - i) >= TCPOLEN_MSS)
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                    && (opt[i+1] == TCPOLEN_MSS)) {
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                        u_int16_t mssval;
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                        mssval = (opt[i+2] << 8) | opt[i+3];
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                        return (mssval >= min && mssval <= max) ^ invert;
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                }
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                if (opt[i] < 2) i++;
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                else i += opt[i+1]?:1;
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        }
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        return invert;
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}
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static int
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match(const struct sk_buff *skb,
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      const struct net_device *in,
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      const struct net_device *out,
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      const void *matchinfo,
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      int offset,
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      const void *hdr,
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      u_int16_t datalen,
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      int *hotdrop)
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{
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        const struct ipt_tcpmss_match_info *info = matchinfo;
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        const struct tcphdr *tcph = (void *)skb->nh.iph + skb->nh.iph->ihl*4;
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        return mssoption_match(info->mss_min, info->mss_max, tcph,
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                               skb->len - skb->nh.iph->ihl*4,
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                               info->invert, hotdrop);
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}
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static inline int find_syn_match(const struct ipt_entry_match *m)
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{
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        const struct ipt_tcp *tcpinfo = (const struct ipt_tcp *)m->data;
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        if (strcmp(m->u.kernel.match->name, "tcp") == 0
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            && (tcpinfo->flg_cmp & TH_SYN)
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            && !(tcpinfo->invflags & IPT_TCP_INV_FLAGS))
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                return 1;
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        return 0;
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}
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static int
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checkentry(const char *tablename,
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           const struct ipt_ip *ip,
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           void *matchinfo,
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           unsigned int matchsize,
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           unsigned int hook_mask)
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{
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        if (matchsize != IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)))
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                return 0;
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        /* Must specify -p tcp */
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        if (ip->proto != IPPROTO_TCP || (ip->invflags & IPT_INV_PROTO)) {
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                printk("tcpmss: Only works on TCP packets\n");
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                return 0;
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        }
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        return 1;
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}
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static struct ipt_match tcpmss_match
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= { { NULL, NULL }, "tcpmss", &match, &checkentry, NULL, THIS_MODULE };
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static int __init init(void)
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{
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        return ipt_register_match(&tcpmss_match);
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}
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static void __exit fini(void)
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{
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        ipt_unregister_match(&tcpmss_match);
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}
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module_init(init);
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module_exit(fini);
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MODULE_LICENSE("GPL");

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