![Florian Westphal](/assets/img/avatar_default.png)
Allow the use of SACK and window scaling when syncookies are used and the client supports tcp timestamps. Options are encoded into the timestamp sent in the syn-ack and restored from the timestamp echo when the ack is received. Based on earlier work by Glenn Griffin. This patch avoids increasing the size of structs by encoding TCP options into the least significant bits of the timestamp and by not using any 'timestamp offset'. The downside is that the timestamp sent in the packet after the synack will increase by several seconds. changes since v1: don't duplicate timestamp echo decoding function, put it into ipv4/syncookie.c and have ipv6/syncookies.c use it. Feedback from Glenn Griffin: fix line indented with spaces, kill redundant if () Reviewed-by: Hagen Paul Pfeifer <hagen@jauu.net> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
280 lines
7.7 KiB
C
280 lines
7.7 KiB
C
/*
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* IPv6 Syncookies implementation for the Linux kernel
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*
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* Authors:
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* Glenn Griffin <ggriffin.kernel@gmail.com>
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*
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* Based on IPv4 implementation by Andi Kleen
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* linux/net/ipv4/syncookies.c
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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*/
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#include <linux/tcp.h>
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#include <linux/random.h>
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#include <linux/cryptohash.h>
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#include <linux/kernel.h>
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#include <net/ipv6.h>
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#include <net/tcp.h>
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extern int sysctl_tcp_syncookies;
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extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
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#define COOKIEBITS 24 /* Upper bits store count */
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#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
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/*
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* This table has to be sorted and terminated with (__u16)-1.
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* XXX generate a better table.
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* Unresolved Issues: HIPPI with a 64k MSS is not well supported.
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*
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* Taken directly from ipv4 implementation.
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* Should this list be modified for ipv6 use or is it close enough?
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* rfc 2460 8.3 suggests mss values 20 bytes less than ipv4 counterpart
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*/
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static __u16 const msstab[] = {
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64 - 1,
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256 - 1,
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512 - 1,
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536 - 1,
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1024 - 1,
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1440 - 1,
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1460 - 1,
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4312 - 1,
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(__u16)-1
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};
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/* The number doesn't include the -1 terminator */
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#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
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/*
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* This (misnamed) value is the age of syncookie which is permitted.
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* Its ideal value should be dependent on TCP_TIMEOUT_INIT and
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* sysctl_tcp_retries1. It's a rather complicated formula (exponential
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* backoff) to compute at runtime so it's currently hardcoded here.
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*/
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#define COUNTER_TRIES 4
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static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
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struct request_sock *req,
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struct dst_entry *dst)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct sock *child;
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child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
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if (child)
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inet_csk_reqsk_queue_add(sk, req, child);
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else
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reqsk_free(req);
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return child;
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}
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static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS];
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static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
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__be16 sport, __be16 dport, u32 count, int c)
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{
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__u32 *tmp = __get_cpu_var(cookie_scratch);
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/*
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* we have 320 bits of information to hash, copy in the remaining
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* 192 bits required for sha_transform, from the syncookie_secret
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* and overwrite the digest with the secret
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*/
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memcpy(tmp + 10, syncookie_secret[c], 44);
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memcpy(tmp, saddr, 16);
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memcpy(tmp + 4, daddr, 16);
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tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
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tmp[9] = count;
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sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
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return tmp[17];
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}
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static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
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__be16 sport, __be16 dport, __u32 sseq,
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__u32 count, __u32 data)
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{
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return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
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sseq + (count << COOKIEBITS) +
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((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
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& COOKIEMASK));
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}
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static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
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struct in6_addr *daddr, __be16 sport,
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__be16 dport, __u32 sseq, __u32 count,
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__u32 maxdiff)
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{
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__u32 diff;
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cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
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diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
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if (diff >= maxdiff)
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return (__u32)-1;
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return (cookie -
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cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
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& COOKIEMASK;
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}
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__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
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{
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struct ipv6hdr *iph = ipv6_hdr(skb);
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const struct tcphdr *th = tcp_hdr(skb);
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int mssind;
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const __u16 mss = *mssp;
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tcp_sk(sk)->last_synq_overflow = jiffies;
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for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
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;
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*mssp = msstab[mssind] + 1;
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NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESSENT);
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return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
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th->dest, ntohl(th->seq),
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jiffies / (HZ * 60), mssind);
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}
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static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
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{
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struct ipv6hdr *iph = ipv6_hdr(skb);
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const struct tcphdr *th = tcp_hdr(skb);
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__u32 seq = ntohl(th->seq) - 1;
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__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
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th->source, th->dest, seq,
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jiffies / (HZ * 60), COUNTER_TRIES);
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return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
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}
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struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
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{
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struct inet_request_sock *ireq;
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struct inet6_request_sock *ireq6;
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struct tcp_request_sock *treq;
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struct ipv6_pinfo *np = inet6_sk(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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const struct tcphdr *th = tcp_hdr(skb);
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__u32 cookie = ntohl(th->ack_seq) - 1;
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struct sock *ret = sk;
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struct request_sock *req;
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int mss;
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struct dst_entry *dst;
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__u8 rcv_wscale;
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struct tcp_options_received tcp_opt;
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if (!sysctl_tcp_syncookies || !th->ack)
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goto out;
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if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) ||
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(mss = cookie_check(skb, cookie)) == 0) {
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NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESFAILED);
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goto out;
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}
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NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV);
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/* check for timestamp cookie support */
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memset(&tcp_opt, 0, sizeof(tcp_opt));
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tcp_parse_options(skb, &tcp_opt, 0);
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if (tcp_opt.saw_tstamp)
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cookie_check_timestamp(&tcp_opt);
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ret = NULL;
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req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
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if (!req)
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goto out;
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ireq = inet_rsk(req);
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ireq6 = inet6_rsk(req);
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treq = tcp_rsk(req);
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ireq6->pktopts = NULL;
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if (security_inet_conn_request(sk, skb, req)) {
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reqsk_free(req);
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goto out;
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}
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req->mss = mss;
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ireq->rmt_port = th->source;
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ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
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ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
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if (ipv6_opt_accepted(sk, skb) ||
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np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
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np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
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atomic_inc(&skb->users);
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ireq6->pktopts = skb;
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}
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ireq6->iif = sk->sk_bound_dev_if;
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/* So that link locals have meaning */
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if (!sk->sk_bound_dev_if &&
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ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
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ireq6->iif = inet6_iif(skb);
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req->expires = 0UL;
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req->retrans = 0;
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ireq->snd_wscale = tcp_opt.snd_wscale;
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ireq->rcv_wscale = tcp_opt.rcv_wscale;
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ireq->sack_ok = tcp_opt.sack_ok;
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ireq->wscale_ok = tcp_opt.wscale_ok;
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ireq->tstamp_ok = tcp_opt.saw_tstamp;
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req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
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treq->rcv_isn = ntohl(th->seq) - 1;
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treq->snt_isn = cookie;
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/*
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* We need to lookup the dst_entry to get the correct window size.
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* This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten
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* me if there is a preferred way.
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*/
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{
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struct in6_addr *final_p = NULL, final;
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struct flowi fl;
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memset(&fl, 0, sizeof(fl));
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fl.proto = IPPROTO_TCP;
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ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
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if (np->opt && np->opt->srcrt) {
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struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt;
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ipv6_addr_copy(&final, &fl.fl6_dst);
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ipv6_addr_copy(&fl.fl6_dst, rt0->addr);
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final_p = &final;
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}
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ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr);
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fl.oif = sk->sk_bound_dev_if;
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fl.fl_ip_dport = inet_rsk(req)->rmt_port;
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fl.fl_ip_sport = inet_sk(sk)->sport;
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security_req_classify_flow(req, &fl);
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if (ip6_dst_lookup(sk, &dst, &fl)) {
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reqsk_free(req);
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goto out;
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}
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if (final_p)
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ipv6_addr_copy(&fl.fl6_dst, final_p);
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if ((xfrm_lookup(&dst, &fl, sk, 0)) < 0)
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goto out;
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}
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req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
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tcp_select_initial_window(tcp_full_space(sk), req->mss,
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&req->rcv_wnd, &req->window_clamp,
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ireq->wscale_ok, &rcv_wscale);
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ireq->rcv_wscale = rcv_wscale;
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ret = get_cookie_sock(sk, skb, req, dst);
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out: return ret;
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}
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