patch-2.4.3 linux/net/ipv4/netfilter/ipt_tcpmss.c

• Lines: 109
• Date: Tue Mar 6 22:44:16 2001
• Orig file: v2.4.2/linux/net/ipv4/netfilter/ipt_tcpmss.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.2/linux/net/ipv4/netfilter/ipt_tcpmss.c linux/net/ipv4/netfilter/ipt_tcpmss.c
@@ -0,0 +1,108 @@
+/* Kernel module to match TCP MSS values. */
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <net/tcp.h>
+
+#include <linux/netfilter_ipv4/ipt_tcpmss.h>
+#include <linux/netfilter_ipv4/ip_tables.h>
+
+#define TH_SYN 0x02
+
+/* Returns 1 if the mss option is set and matched by the range, 0 otherwise */
+static inline int
+mssoption_match(u_int16_t min, u_int16_t max,
+		const struct tcphdr *tcp,
+		u_int16_t datalen,
+		int invert,
+		int *hotdrop)
+{
+	unsigned int i;
+	const u_int8_t *opt = (u_int8_t *)tcp;
+
+	/* If we don't have the whole header, drop packet. */
+	if (tcp->doff * 4 > datalen) {
+		*hotdrop = 1;
+		return 0;
+	}
+
+	for (i = sizeof(struct tcphdr); i < tcp->doff * 4; ) {
+		if ((opt[i] == TCPOPT_MSS)
+		    && ((tcp->doff * 4 - i) >= TCPOLEN_MSS)
+		    && (opt[i+1] == TCPOLEN_MSS)) {
+			u_int16_t mssval;
+
+			mssval = (opt[i+2] << 8) | opt[i+3];
+			
+			return (mssval >= min && mssval <= max) ^ invert;
+		}
+		if (opt[i] < 2) i++;
+		else i += opt[i+1]?:1;
+	}
+
+	return invert;
+}
+
+static int
+match(const struct sk_buff *skb,
+      const struct net_device *in,
+      const struct net_device *out,
+      const void *matchinfo,
+      int offset,
+      const void *hdr,
+      u_int16_t datalen,
+      int *hotdrop)
+{
+	const struct ipt_tcpmss_match_info *info = matchinfo;
+	const struct tcphdr *tcph = (void *)skb->nh.iph + skb->nh.iph->ihl*4;
+
+	return mssoption_match(info->mss_min, info->mss_max, tcph,
+			       skb->len - skb->nh.iph->ihl*4,
+			       info->invert, hotdrop);
+}
+
+static inline int find_syn_match(const struct ipt_entry_match *m)
+{
+	const struct ipt_tcp *tcpinfo = (const struct ipt_tcp *)m->data;
+
+	if (strcmp(m->u.kernel.match->name, "tcp") == 0
+	    && (tcpinfo->flg_cmp & TH_SYN)
+	    && !(tcpinfo->invflags & IPT_TCP_INV_FLAGS))
+		return 1;
+
+	return 0;
+}
+
+static int
+checkentry(const char *tablename,
+           const struct ipt_ip *ip,
+           void *matchinfo,
+           unsigned int matchsize,
+           unsigned int hook_mask)
+{
+	if (matchsize != IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)))
+		return 0;
+
+	/* Must specify -p tcp */
+	if (ip->proto != IPPROTO_TCP || (ip->invflags & IPT_INV_PROTO)) {
+		printk("tcpmss: Only works on TCP packets\n");
+		return 0;
+	}
+
+	return 1;
+}
+
+static struct ipt_match tcpmss_match
+= { { NULL, NULL }, "tcpmss", &match, &checkentry, NULL, THIS_MODULE };
+
+static int __init init(void)
+{
+	return ipt_register_match(&tcpmss_match);
+}
+
+static void __exit fini(void)
+{
+	ipt_unregister_match(&tcpmss_match);
+}
+
+module_init(init);
+module_exit(fini);