summaryrefslogtreecommitdiff
path: root/net/ipv4/netfilter/ipt_tcpmss.c
diff options
context:
space:
mode:
Diffstat (limited to 'net/ipv4/netfilter/ipt_tcpmss.c')
-rw-r--r--net/ipv4/netfilter/ipt_tcpmss.c127
1 files changed, 127 insertions, 0 deletions
diff --git a/net/ipv4/netfilter/ipt_tcpmss.c b/net/ipv4/netfilter/ipt_tcpmss.c
new file mode 100644
index 00000000000..4dc9b16ab4a
--- /dev/null
+++ b/net/ipv4/netfilter/ipt_tcpmss.c
@@ -0,0 +1,127 @@
+/* Kernel module to match TCP MSS values. */
+
+/* Copyright (C) 2000 Marc Boucher <marc@mbsi.ca>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#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
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Marc Boucher <marc@mbsi.ca>");
+MODULE_DESCRIPTION("iptables TCP MSS match module");
+
+/* 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 sk_buff *skb,
+ int invert,
+ int *hotdrop)
+{
+ struct tcphdr _tcph, *th;
+ /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
+ u8 _opt[15 * 4 - sizeof(_tcph)], *op;
+ unsigned int i, optlen;
+
+ /* If we don't have the whole header, drop packet. */
+ th = skb_header_pointer(skb, skb->nh.iph->ihl * 4,
+ sizeof(_tcph), &_tcph);
+ if (th == NULL)
+ goto dropit;
+
+ /* Malformed. */
+ if (th->doff*4 < sizeof(*th))
+ goto dropit;
+
+ optlen = th->doff*4 - sizeof(*th);
+ if (!optlen)
+ goto out;
+
+ /* Truncated options. */
+ op = skb_header_pointer(skb, skb->nh.iph->ihl * 4 + sizeof(*th),
+ optlen, _opt);
+ if (op == NULL)
+ goto dropit;
+
+ for (i = 0; i < optlen; ) {
+ if (op[i] == TCPOPT_MSS
+ && (optlen - i) >= TCPOLEN_MSS
+ && op[i+1] == TCPOLEN_MSS) {
+ u_int16_t mssval;
+
+ mssval = (op[i+2] << 8) | op[i+3];
+
+ return (mssval >= min && mssval <= max) ^ invert;
+ }
+ if (op[i] < 2) i++;
+ else i += op[i+1]?:1;
+ }
+out:
+ return invert;
+
+ dropit:
+ *hotdrop = 1;
+ return 0;
+}
+
+static int
+match(const struct sk_buff *skb,
+ const struct net_device *in,
+ const struct net_device *out,
+ const void *matchinfo,
+ int offset,
+ int *hotdrop)
+{
+ const struct ipt_tcpmss_match_info *info = matchinfo;
+
+ return mssoption_match(info->mss_min, info->mss_max, skb,
+ info->invert, hotdrop);
+}
+
+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 = {
+ .name = "tcpmss",
+ .match = &match,
+ .checkentry = &checkentry,
+ .me = 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);