Re: [PATCH] Add IPv6 support to TCP SYN cookies

From: Glenn Griffin
Date: Fri Feb 08 2008 - 00:42:24 EST

Updated to incorporate Eric's suggestion of using a per cpu buffer
rather than allocating on the stack. Just a two line change, but will
resend in it's entirety.

Signed-off-by: Glenn Griffin <ggriffin.kernel@xxxxxxxxx>
---
include/net/tcp.h | 8 ++
net/ipv4/syncookies.c | 7 +-
net/ipv4/tcp_input.c | 1 +
net/ipv4/tcp_minisocks.c | 2 +
net/ipv4/tcp_output.c | 1 +
net/ipv6/Makefile | 1 +
net/ipv6/syncookies.c | 267 ++++++++++++++++++++++++++++++++++++++++++++++
net/ipv6/tcp_ipv6.c | 77 ++++++++++----
8 files changed, 338 insertions(+), 26 deletions(-)
create mode 100644 net/ipv6/syncookies.c

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7de4ea3..c428ec7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -29,6 +29,7 @@
#include <linux/skbuff.h>
#include <linux/dmaengine.h>
#include <linux/crypto.h>
+#include <linux/cryptohash.h>

#include <net/inet_connection_sock.h>
#include <net/inet_timewait_sock.h>
@@ -434,11 +435,17 @@ extern int tcp_disconnect(struct sock *sk, int flags);
extern void tcp_unhash(struct sock *sk);

/* From syncookies.c */
+extern __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
extern struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
struct ip_options *opt);
extern __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb,
__u16 *mss);

+/* From net/ipv6/syncookies.c */
+extern struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
+extern __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb,
+ __u16 *mss);
+
/* tcp_output.c */

extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
@@ -1332,6 +1339,7 @@ extern int tcp_proc_register(struct tcp_seq_afinfo *afinfo);
extern void tcp_proc_unregister(struct tcp_seq_afinfo *afinfo);

extern struct request_sock_ops tcp_request_sock_ops;
+extern struct request_sock_ops tcp6_request_sock_ops;

extern int tcp_v4_destroy_sock(struct sock *sk);

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index f470fe4..cc6637b 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -10,8 +10,6 @@
* 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>
@@ -23,14 +21,15 @@

extern int sysctl_tcp_syncookies;

-static __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
+__u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
+EXPORT_SYMBOL(syncookie_secret);

static __init int init_syncookies(void)
{
get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
return 0;
}
-module_init(init_syncookies);
+__initcall(init_syncookies);

#define COOKIEBITS 24 /* Upper bits store count */
#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 19c449f..93e128c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5326,6 +5326,7 @@ discard:

EXPORT_SYMBOL(sysctl_tcp_ecn);
EXPORT_SYMBOL(sysctl_tcp_reordering);
+EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
EXPORT_SYMBOL(tcp_parse_options);
EXPORT_SYMBOL(tcp_rcv_established);
EXPORT_SYMBOL(tcp_rcv_state_process);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b61b768..0f494cd 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -35,6 +35,8 @@
#endif

int sysctl_tcp_syncookies __read_mostly = SYNC_INIT;
+EXPORT_SYMBOL(sysctl_tcp_syncookies);
+
int sysctl_tcp_abort_on_overflow __read_mostly;

struct inet_timewait_death_row tcp_death_row = {
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ed750f9..cbfef8b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2560,6 +2560,7 @@ void tcp_send_probe0(struct sock *sk)
}
}

+EXPORT_SYMBOL(tcp_select_initial_window);
EXPORT_SYMBOL(tcp_connect);
EXPORT_SYMBOL(tcp_make_synack);
EXPORT_SYMBOL(tcp_simple_retransmit);
diff --git a/net/ipv6/Makefile b/net/ipv6/Makefile
index 24f3aa0..ae14617 100644
--- a/net/ipv6/Makefile
+++ b/net/ipv6/Makefile
@@ -16,6 +16,7 @@ ipv6-$(CONFIG_XFRM) += xfrm6_policy.o xfrm6_state.o xfrm6_input.o \
ipv6-$(CONFIG_NETFILTER) += netfilter.o
ipv6-$(CONFIG_IPV6_MULTIPLE_TABLES) += fib6_rules.o
ipv6-$(CONFIG_PROC_FS) += proc.o
+ipv6-$(CONFIG_SYN_COOKIES) += syncookies.o

ipv6-objs += $(ipv6-y)

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
new file mode 100644
index 0000000..063dade
--- /dev/null
+++ b/net/ipv6/syncookies.c
@@ -0,0 +1,267 @@
+/*
+ * IPv6 Syncookies implementation for the Linux kernel
+ *
+ * Authors:
+ * Glenn Griffin <ggriffin.kernel@xxxxxxxxx>
+ *
+ * Based on IPv4 implementation by Andi Kleen
+ * linux/net/ipv4/syncookies.c
+ *
+ * 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.
+ *
+ */
+
+#include <linux/tcp.h>
+#include <linux/random.h>
+#include <linux/cryptohash.h>
+#include <linux/kernel.h>
+#include <net/ipv6.h>
+#include <net/tcp.h>
+
+extern int sysctl_tcp_syncookies;
+extern __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
+
+#define COOKIEBITS 24 /* Upper bits store count */
+#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
+
+/*
+ * 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.
+ *
+ * Taken directly from ipv4 implementation.
+ * Should this list be modified for ipv6 use or is it close enough?
+ * rfc 2460 8.3 suggests mss values 20 bytes less than ipv4 counterpart
+ */
+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)
+
+/*
+ * 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
+
+static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
+ struct request_sock *req,
+ struct dst_entry *dst)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct sock *child;
+
+ child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
+ if (child)
+ inet_csk_reqsk_queue_add(sk, req, child);
+ else
+ reqsk_free(req);
+
+ return child;
+}
+
+static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS];
+
+static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
+ __be16 sport, __be16 dport, u32 count, int c)
+{
+ __u32 *tmp = __get_cpu_var(cookie_scratch);
+
+ /*
+ * we have 320 bits of information to hash, copy in the remaining
+ * 192 bits required for sha_transform, from the syncookie_secret
+ * and overwrite the digest with the secret
+ */
+ memcpy(tmp + 10, syncookie_secret[c], 44);
+ memcpy(tmp, saddr, 16);
+ memcpy(tmp + 4, daddr, 16);
+ tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
+ tmp[9] = count;
+ sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
+
+ return tmp[17];
+}
+
+static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
+ __be16 sport, __be16 dport, __u32 sseq,
+ __u32 count, __u32 data)
+{
+ return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
+ sseq + (count << COOKIEBITS) +
+ ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
+ & COOKIEMASK));
+}
+
+static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
+ struct in6_addr *daddr, __be16 sport,
+ __be16 dport, __u32 sseq, __u32 count,
+ __u32 maxdiff)
+{
+ __u32 diff;
+
+ cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
+
+ 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;
+}
+
+__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
+{
+ struct ipv6hdr *iph = ipv6_hdr(skb);
+ const struct tcphdr *th = tcp_hdr(skb);
+ int mssind;
+ const __u16 mss = *mssp;
+
+ tcp_sk(sk)->last_synq_overflow = jiffies;
+
+ for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
+ ;
+ *mssp = msstab[mssind] + 1;
+
+ NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESSENT);
+
+ return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
+ th->dest, ntohl(th->seq),
+ jiffies / (HZ * 60), mssind);
+}
+
+static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
+{
+ struct ipv6hdr *iph = ipv6_hdr(skb);
+ const struct tcphdr *th = tcp_hdr(skb);
+ __u32 seq = ntohl(th->seq) - 1;
+ __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
+ th->source, th->dest, seq,
+ jiffies / (HZ * 60), COUNTER_TRIES);
+
+ return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
+}
+
+struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
+{
+ struct inet_request_sock *ireq;
+ struct inet6_request_sock *ireq6;
+ struct tcp_request_sock *treq;
+ struct ipv6_pinfo *np = inet6_sk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ const struct tcphdr *th = tcp_hdr(skb);
+ __u32 cookie = ntohl(th->ack_seq) - 1;
+ struct sock *ret = sk;
+ struct request_sock *req;
+ int mss;
+ struct dst_entry *dst;
+ __u8 rcv_wscale;
+
+ if (!sysctl_tcp_syncookies || !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);
+
+ ret = NULL;
+ req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
+ if (!req)
+ goto out;
+
+ ireq = inet_rsk(req);
+ ireq6 = inet6_rsk(req);
+ treq = tcp_rsk(req);
+ ireq6->pktopts = NULL;
+
+ if (security_inet_conn_request(sk, skb, req)) {
+ reqsk_free(req);
+ goto out;
+ }
+
+ req->mss = mss;
+ ireq->rmt_port = th->source;
+ ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
+ ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
+ if (ipv6_opt_accepted(sk, skb) ||
+ np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
+ np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
+ atomic_inc(&skb->users);
+ ireq6->pktopts = skb;
+ }
+
+ ireq6->iif = sk->sk_bound_dev_if;
+ /* So that link locals have meaning */
+ if (!sk->sk_bound_dev_if &&
+ ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
+ ireq6->iif = inet6_iif(skb);
+
+ req->expires = 0UL;
+ req->retrans = 0;
+ ireq->snd_wscale = ireq->rcv_wscale = ireq->tstamp_ok = 0;
+ ireq->wscale_ok = ireq->sack_ok = 0;
+ treq->rcv_isn = ntohl(th->seq) - 1;
+ treq->snt_isn = cookie;
+
+ /*
+ * We need to lookup the dst_entry to get the correct window size.
+ * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
+ * me if there is a preferred way.
+ */
+ {
+ struct in6_addr *final_p = NULL, final;
+ struct flowi fl;
+ memset(&fl, 0, sizeof(fl));
+ fl.proto = IPPROTO_TCP;
+ ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
+ if (np->opt && np->opt->srcrt) {
+ struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt;
+ ipv6_addr_copy(&final, &fl.fl6_dst);
+ ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
+ final_p = &final;
+ }
+ ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr);
+ fl.oif = sk->sk_bound_dev_if;
+ fl.fl_ip_dport = inet_rsk(req)->rmt_port;
+ fl.fl_ip_sport = inet_sk(sk)->sport;
+ security_req_classify_flow(req, &fl);
+ if (ip6_dst_lookup(sk, &dst, &fl)) {
+ reqsk_free(req);
+ goto out;
+ }
+ if (final_p)
+ ipv6_addr_copy(&fl.fl6_dst, final_p);
+ if ((xfrm_lookup(&dst, &fl, sk, 0)) < 0)
+ goto out;
+ }
+
+ req->window_clamp = dst_metric(dst, RTAX_WINDOW);
+ tcp_select_initial_window(tcp_full_space(sk), req->mss,
+ &req->rcv_wnd, &req->window_clamp,
+ 0, &rcv_wscale);
+
+ ireq->rcv_wscale = rcv_wscale;
+
+ ret = get_cookie_sock(sk, skb, req, dst);
+
+out: return ret;
+}
+
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 12750f2..1f4e544 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -514,6 +514,20 @@ done:
return err;
}

+static inline void syn_flood_warning(struct sk_buff *skb)
+{
+#ifdef CONFIG_SYN_COOKIES
+ if (sysctl_tcp_syncookies)
+ printk(KERN_INFO
+ "TCPv6: Possible SYN flooding on port %d. "
+ "Sending cookies.\n", ntohs(tcp_hdr(skb)->dest));
+ else
+#endif
+ printk(KERN_INFO
+ "TCPv6: Possible SYN flooding on port %d. "
+ "Dropping request.\n", ntohs(tcp_hdr(skb)->dest));
+}
+
static void tcp_v6_reqsk_destructor(struct request_sock *req)
{
if (inet6_rsk(req)->pktopts)
@@ -917,7 +931,7 @@ done_opts:
}
#endif

-static struct request_sock_ops tcp6_request_sock_ops __read_mostly = {
+struct request_sock_ops tcp6_request_sock_ops __read_mostly = {
.family = AF_INET6,
.obj_size = sizeof(struct tcp6_request_sock),
.rtx_syn_ack = tcp_v6_send_synack,
@@ -1215,9 +1229,9 @@ static struct sock *tcp_v6_hnd_req(struct sock *sk,struct sk_buff *skb)
return NULL;
}

-#if 0 /*def CONFIG_SYN_COOKIES*/
+#ifdef CONFIG_SYN_COOKIES
if (!th->rst && !th->syn && th->ack)
- sk = cookie_v6_check(sk, skb, &(IPCB(skb)->opt));
+ sk = cookie_v6_check(sk, skb);
#endif
return sk;
}
@@ -1233,6 +1247,11 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
struct tcp_sock *tp = tcp_sk(sk);
struct request_sock *req = NULL;
__u32 isn = TCP_SKB_CB(skb)->when;
+#ifdef CONFIG_SYN_COOKIES
+ int want_cookie = 0;
+#else
+#define want_cookie 0
+#endif

if (skb->protocol == htons(ETH_P_IP))
return tcp_v4_conn_request(sk, skb);
@@ -1240,12 +1259,14 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
if (!ipv6_unicast_destination(skb))
goto drop;

- /*
- * There are no SYN attacks on IPv6, yet...
- */
if (inet_csk_reqsk_queue_is_full(sk) && !isn) {
if (net_ratelimit())
- printk(KERN_INFO "TCPv6: dropping request, synflood is possible\n");
+ syn_flood_warning(skb);
+#ifdef CONFIG_SYN_COOKIES
+ if (sysctl_tcp_syncookies)
+ want_cookie = 1;
+ else
+#endif
goto drop;
}

@@ -1266,29 +1287,39 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)

tcp_parse_options(skb, &tmp_opt, 0);

+ if (want_cookie) {
+ tcp_clear_options(&tmp_opt);
+ tmp_opt.saw_tstamp = 0;
+ }
+
tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
tcp_openreq_init(req, &tmp_opt, skb);

treq = inet6_rsk(req);
ipv6_addr_copy(&treq->rmt_addr, &ipv6_hdr(skb)->saddr);
ipv6_addr_copy(&treq->loc_addr, &ipv6_hdr(skb)->daddr);
- TCP_ECN_create_request(req, tcp_hdr(skb));
treq->pktopts = NULL;
- if (ipv6_opt_accepted(sk, skb) ||
- np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
- np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
- atomic_inc(&skb->users);
- treq->pktopts = skb;
- }
- treq->iif = sk->sk_bound_dev_if;
+ if (!want_cookie)
+ TCP_ECN_create_request(req, tcp_hdr(skb));
+
+ if (want_cookie) {
+ isn = cookie_v6_init_sequence(sk, skb, &req->mss);
+ } else if (!isn) {
+ if (ipv6_opt_accepted(sk, skb) ||
+ np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
+ np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
+ atomic_inc(&skb->users);
+ treq->pktopts = skb;
+ }
+ treq->iif = sk->sk_bound_dev_if;

- /* So that link locals have meaning */
- if (!sk->sk_bound_dev_if &&
- ipv6_addr_type(&treq->rmt_addr) & IPV6_ADDR_LINKLOCAL)
- treq->iif = inet6_iif(skb);
+ /* So that link locals have meaning */
+ if (!sk->sk_bound_dev_if &&
+ ipv6_addr_type(&treq->rmt_addr) & IPV6_ADDR_LINKLOCAL)
+ treq->iif = inet6_iif(skb);

- if (isn == 0)
isn = tcp_v6_init_sequence(skb);
+ }

tcp_rsk(req)->snt_isn = isn;

@@ -1297,8 +1328,10 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
if (tcp_v6_send_synack(sk, req, NULL))
goto drop;

- inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
- return 0;
+ if (!want_cookie) {
+ inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+ return 0;
+ }

drop:
if (req)
--
1.5.3.4

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