281 lines
7.7 KiB
C
281 lines
7.7 KiB
C
/*
|
|
* 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 request_sock_ops tcp_request_sock_ops;
|
|
|
|
static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
|
|
struct request_sock *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
|
|
reqsk_free(req);
|
|
|
|
return child;
|
|
}
|
|
|
|
struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
|
|
struct ip_options *opt)
|
|
{
|
|
struct inet_request_sock *ireq;
|
|
struct tcp_request_sock *treq;
|
|
struct tcp_sock *tp = tcp_sk(sk);
|
|
__u32 cookie = ntohl(skb->h.th->ack_seq) - 1;
|
|
struct sock *ret = sk;
|
|
struct request_sock *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);
|
|
|
|
ret = NULL;
|
|
req = reqsk_alloc(&tcp_request_sock_ops); /* for safety */
|
|
if (!req)
|
|
goto out;
|
|
|
|
ireq = inet_rsk(req);
|
|
treq = tcp_rsk(req);
|
|
treq->rcv_isn = htonl(skb->h.th->seq) - 1;
|
|
treq->snt_isn = cookie;
|
|
req->mss = mss;
|
|
ireq->rmt_port = skb->h.th->source;
|
|
ireq->loc_addr = skb->nh.iph->daddr;
|
|
ireq->rmt_addr = skb->nh.iph->saddr;
|
|
ireq->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;
|
|
|
|
ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
|
|
if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
|
|
kfree(ireq->opt);
|
|
ireq->opt = NULL;
|
|
}
|
|
}
|
|
|
|
ireq->snd_wscale = ireq->rcv_wscale = ireq->tstamp_ok = 0;
|
|
ireq->wscale_ok = ireq->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 :
|
|
ireq->rmt_addr),
|
|
.saddr = ireq->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)) {
|
|
reqsk_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 */
|
|
ireq->rcv_wscale = rcv_wscale;
|
|
|
|
ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
|
|
out: return ret;
|
|
}
|