Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
new file mode 100644
index 0000000..e923d2f
--- /dev/null
+++ b/net/ipv4/syncookies.c
@@ -0,0 +1,279 @@
+/*
+ * 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 1.18 2002/02/01 22:01:04 davem Exp $
+ *
+ * Missing: IPv6 support.
+ */
+
+#include <linux/tcp.h>
+#include <linux/slab.h>
+#include <linux/random.h>
+#include <linux/cryptohash.h>
+#include <linux/kernel.h>
+#include <net/tcp.h>
+
+extern int sysctl_tcp_syncookies;
+
+static __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
+
+static __init int init_syncookies(void)
+{
+ get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
+ return 0;
+}
+module_init(init_syncookies);
+
+#define COOKIEBITS 24 /* Upper bits store count */
+#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
+
+static u32 cookie_hash(u32 saddr, u32 daddr, u32 sport, u32 dport,
+ u32 count, int c)
+{
+ __u32 tmp[16 + 5 + SHA_WORKSPACE_WORDS];
+
+ memcpy(tmp + 3, syncookie_secret[c], sizeof(syncookie_secret[c]));
+ tmp[0] = saddr;
+ tmp[1] = daddr;
+ tmp[2] = (sport << 16) + dport;
+ tmp[3] = count;
+ sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
+
+ return tmp[17];
+}
+
+static __u32 secure_tcp_syn_cookie(__u32 saddr, __u32 daddr, __u16 sport,
+ __u16 dport, __u32 sseq, __u32 count,
+ __u32 data)
+{
+ /*
+ * Compute the secure sequence number.
+ * The output should be:
+ * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
+ * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
+ * Where sseq is their sequence number and count increases every
+ * minute by 1.
+ * As an extra hack, we add a small "data" value that encodes the
+ * MSS into the second hash value.
+ */
+
+ return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
+ sseq + (count << COOKIEBITS) +
+ ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
+ & COOKIEMASK));
+}
+
+/*
+ * This retrieves the small "data" value from the syncookie.
+ * If the syncookie is bad, the data returned will be out of
+ * range. This must be checked by the caller.
+ *
+ * The count value used to generate the cookie must be within
+ * "maxdiff" if the current (passed-in) "count". The return value
+ * is (__u32)-1 if this test fails.
+ */
+static __u32 check_tcp_syn_cookie(__u32 cookie, __u32 saddr, __u32 daddr,
+ __u16 sport, __u16 dport, __u32 sseq,
+ __u32 count, __u32 maxdiff)
+{
+ __u32 diff;
+
+ /* Strip away the layers from the cookie */
+ cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
+
+ /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
+ diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS);
+ if (diff >= maxdiff)
+ return (__u32)-1;
+
+ return (cookie -
+ cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
+ & COOKIEMASK; /* Leaving the data behind */
+}
+
+/*
+ * This table has to be sorted and terminated with (__u16)-1.
+ * XXX generate a better table.
+ * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
+ */
+static __u16 const msstab[] = {
+ 64 - 1,
+ 256 - 1,
+ 512 - 1,
+ 536 - 1,
+ 1024 - 1,
+ 1440 - 1,
+ 1460 - 1,
+ 4312 - 1,
+ (__u16)-1
+};
+/* The number doesn't include the -1 terminator */
+#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
+
+/*
+ * Generate a syncookie. mssp points to the mss, which is returned
+ * rounded down to the value encoded in the cookie.
+ */
+__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int mssind;
+ const __u16 mss = *mssp;
+
+
+ tp->last_synq_overflow = jiffies;
+
+ /* XXX sort msstab[] by probability? Binary search? */
+ for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
+ ;
+ *mssp = msstab[mssind] + 1;
+
+ NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESSENT);
+
+ return secure_tcp_syn_cookie(skb->nh.iph->saddr, skb->nh.iph->daddr,
+ skb->h.th->source, skb->h.th->dest,
+ ntohl(skb->h.th->seq),
+ jiffies / (HZ * 60), mssind);
+}
+
+/*
+ * This (misnamed) value is the age of syncookie which is permitted.
+ * Its ideal value should be dependent 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.
+ * Return the decoded mss if it is, or 0 if not.
+ */
+static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
+{
+ __u32 seq;
+ __u32 mssind;
+
+ seq = ntohl(skb->h.th->seq)-1;
+ mssind = check_tcp_syn_cookie(cookie,
+ skb->nh.iph->saddr, skb->nh.iph->daddr,
+ skb->h.th->source, skb->h.th->dest,
+ seq, jiffies / (HZ * 60), COUNTER_TRIES);
+
+ return mssind < NUM_MSS ? msstab[mssind] + 1 : 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_sock *tp = tcp_sk(sk);
+ struct sock *child;
+
+ child = tp->af_specific->syn_recv_sock(sk, skb, req, dst);
+ if (child)
+ tcp_acceptq_queue(sk, req, child);
+ else
+ tcp_openreq_free(req);
+
+ return child;
+}
+
+struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
+ struct ip_options *opt)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ __u32 cookie = ntohl(skb->h.th->ack_seq) - 1;
+ struct sock *ret = sk;
+ struct open_request *req;
+ int mss;
+ struct rtable *rt;
+ __u8 rcv_wscale;
+
+ if (!sysctl_tcp_syncookies || !skb->h.th->ack)
+ goto out;
+
+ if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) ||
+ (mss = cookie_check(skb, cookie)) == 0) {
+ NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESFAILED);
+ goto out;
+ }
+
+ NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV);
+
+ req = tcp_openreq_alloc();
+ ret = NULL;
+ if (!req)
+ goto out;
+
+ 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 */
+ req->af.v4_req.opt = NULL;
+
+ /* 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(req->af.v4_req.opt);
+ req->af.v4_req.opt = NULL;
+ }
+ }
+ }
+
+ req->snd_wscale = req->rcv_wscale = req->tstamp_ok = 0;
+ req->wscale_ok = req->sack_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.
+ */
+ {
+ struct flowi fl = { .nl_u = { .ip4_u =
+ { .daddr = ((opt && opt->srr) ?
+ opt->faddr :
+ req->af.v4_req.rmt_addr),
+ .saddr = req->af.v4_req.loc_addr,
+ .tos = RT_CONN_FLAGS(sk) } },
+ .proto = IPPROTO_TCP,
+ .uli_u = { .ports =
+ { .sport = skb->h.th->dest,
+ .dport = skb->h.th->source } } };
+ if (ip_route_output_key(&rt, &fl)) {
+ tcp_openreq_free(req);
+ goto out;
+ }
+ }
+
+ /* Try to redo what tcp_v4_send_synack did. */
+ req->window_clamp = dst_metric(&rt->u.dst, RTAX_WINDOW);
+ tcp_select_initial_window(tcp_full_space(sk), req->mss,
+ &req->rcv_wnd, &req->window_clamp,
+ 0, &rcv_wscale);
+ /* BTW win scale with syncookies is 0 by definition */
+ req->rcv_wscale = rcv_wscale;
+
+ ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
+out: return ret;
+}