patch-2.1.44 linux/net/ipv4/syncookies.c

• Lines: 219
• Date: Thu Jun 26 12:33:41 1997
• Orig file: v2.1.43/linux/net/ipv4/syncookies.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.1.43/linux/net/ipv4/syncookies.c linux/net/ipv4/syncookies.c
@@ -0,0 +1,218 @@
+/*
+ *  Syncookies implementation for the Linux kernel
+ *
+ *  Copyright (C) 1997 Andi Kleen
+ *  Based on ideas by D.J.Bernstein and Eric Schenk. 
+ *
+ *	This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ * 
+ *  $Id: syncookies.c,v 1.1 1997/06/06 20:37:56 freitag Exp $
+ *
+ *  Missing: IPv6 support. 
+ *           Some counter so that the Administrator can see when the machine
+ *           is under a syn flood attack.
+ */
+
+#include <linux/config.h>
+#if defined(CONFIG_SYN_COOKIES) 
+#include <linux/tcp.h>
+#include <linux/malloc.h>
+#include <linux/random.h>
+#include <net/tcp.h>
+
+extern int sysctl_tcp_syncookies;
+
+static unsigned long tcp_lastsynq_overflow;
+
+/* 
+ * This table has to be sorted. Only 8 entries are allowed and the
+ * last entry has to be duplicated.
+ * XXX generate a better table.
+ * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
+ */
+static __u16 const msstab[] = {
+	64,
+	256,	
+	512,	
+	536,
+	1024,	
+	1440,	
+	1460,	
+	4312,
+	4312 
+};
+
+static __u32 make_syncookie(struct sk_buff *skb,  __u32 counter, __u32 seq)
+{
+	__u32 z;
+
+	z = secure_tcp_syn_cookie(skb->nh.iph->saddr, skb->nh.iph->daddr,
+				  skb->h.th->source, skb->h.th->dest,
+				  seq, 
+				  counter);
+
+#if 0
+	printk(KERN_DEBUG 
+	       "msc: z=%u,cnt=%u,seq=%u,sadr=%u,dadr=%u,sp=%u,dp=%u\n",
+	       z,counter,seq,
+	       skb->nh.iph->saddr,skb->nh.iph->daddr,
+	       ntohs(skb->h.th->source), ntohs(skb->h.th->dest));
+#endif
+
+	return z;
+}
+
+/*
+ * Generate a syncookie. 
+ */
+__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, 
+			      __u16 *mssp)
+{
+	int i; 
+	__u32 isn; 
+	const __u16 mss = *mssp, *w; 
+
+	tcp_lastsynq_overflow = jiffies;
+
+	isn = make_syncookie(skb, (jiffies/HZ) >> 6, ntohl(skb->h.th->seq));
+	
+	/* XXX sort msstab[] by probability? */
+	w = msstab;
+	for (i = 0; i < 8; i++) 
+		if (mss >= *w && mss < *++w)
+			goto found;
+	i--;
+found:
+	*mssp = w[-1]; 
+
+	isn |= i; 
+	return isn; 
+}
+
+/* This value should be dependant on TCP_TIMEOUT_INIT and 
+ * sysctl_tcp_retries1. It's a rather complicated formula 
+ * (exponential backoff) to compute at runtime so it's currently hardcoded
+ * here.
+ */
+#define COUNTER_TRIES 4
+
+/*  
+ * Check if a ack sequence number is a valid syncookie. 
+ */
+static inline int cookie_check(struct sk_buff *skb, __u32 cookie) 
+{
+	int mssind; 
+	int i; 
+	__u32 counter; 
+	__u32 seq; 
+
+  	if ((jiffies - tcp_lastsynq_overflow) > TCP_TIMEOUT_INIT
+	    && tcp_lastsynq_overflow) 
+		return 0; 
+
+	mssind = cookie & 7;
+	cookie &= ~7;
+
+	counter = (jiffies/HZ)>>6; 
+	seq = ntohl(skb->h.th->seq)-1; 
+	for (i = 0; i < COUNTER_TRIES; i++)
+	    if (make_syncookie(skb, counter-i, seq) == cookie)
+		    return msstab[mssind];	
+
+	return 0;
+}
+
+extern struct or_calltable or_ipv4;
+
+static inline struct sock *
+get_cookie_sock(struct sock *sk, struct sk_buff *skb, struct open_request *req,
+		struct dst_entry *dst)
+{
+	struct tcp_opt *tp = &sk->tp_pinfo.af_tcp;
+
+	sk = tp->af_specific->syn_recv_sock(sk, skb, req, dst);
+	req->sk = sk; 
+	
+	/* Queue up for accept() */
+	tcp_synq_queue(tp, req);
+	
+	return sk; 
+}
+
+struct sock *
+cookie_v4_check(struct sock *sk, struct sk_buff *skb, struct ip_options *opt)
+{
+	__u32 cookie = ntohl(skb->h.th->ack_seq)-1; 
+	struct open_request *req; 
+	int mss; 
+	struct rtable *rt; 
+
+	if (!sysctl_tcp_syncookies)
+		return sk;
+	if (!skb->h.th->ack)
+		return sk; 
+
+	mss = cookie_check(skb, cookie);
+	if (mss == 0) 
+		return sk;
+
+	req = tcp_openreq_alloc();
+	if (req == NULL)
+		return NULL;	
+
+	req->rcv_isn = htonl(skb->h.th->seq)-1;
+	req->snt_isn = cookie; 
+	req->mss = mss;
+ 	req->rmt_port = skb->h.th->source;
+	req->af.v4_req.loc_addr = skb->nh.iph->daddr;
+	req->af.v4_req.rmt_addr = skb->nh.iph->saddr;
+	req->class = &or_ipv4; /* for savety */
+
+	/* We throwed the options of the initial SYN away, so we hope
+	 * the ACK carries the same options again (see RFC1122 4.2.3.8)
+	 */
+	if (opt && opt->optlen) {
+		int opt_size = sizeof(struct ip_options) + opt->optlen;
+
+		req->af.v4_req.opt = kmalloc(opt_size, GFP_ATOMIC);
+		if (req->af.v4_req.opt) {
+			if (ip_options_echo(req->af.v4_req.opt, skb)) {
+				kfree_s(req->af.v4_req.opt, opt_size);
+				req->af.v4_req.opt = NULL;
+			}
+		}
+	}
+	
+	req->af.v4_req.opt = NULL;
+	req->snd_wscale = req->rcv_wscale = req->tstamp_ok = 0;
+	req->wscale_ok = 0; 
+	req->expires = 0UL; 
+	req->retrans = 0; 
+	
+	/*
+	 * We need to lookup the route here to get at the correct
+	 * window size. We should better make sure that the window size
+	 * hasn't changed since we received the original syn, but I see
+	 * no easy way to do this. 
+	 */
+	if (ip_route_output(&rt,
+			    opt && opt->srr ? opt->faddr : 
+			    req->af.v4_req.rmt_addr,req->af.v4_req.loc_addr,
+			    sk->ip_tos, NULL)) {
+	    tcp_openreq_free(req);
+	    return NULL; 
+	}
+
+	/* Try to redo what tcp_v4_send_synack did. */
+	req->window_clamp = rt->u.dst.window;  
+	tcp_select_initial_window(sock_rspace(sk)/2,req->mss,
+				  &req->rcv_wnd, &req->window_clamp, 
+				  0, &req->rcv_wscale);
+
+	return get_cookie_sock(sk, skb, req, &rt->u.dst);
+}
+
+#endif