diff options
Diffstat (limited to 'net/ipv6/syncookies.c')
| -rw-r--r-- | net/ipv6/syncookies.c | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c new file mode 100644 index 000000000..ca291e342 --- /dev/null +++ b/net/ipv6/syncookies.c @@ -0,0 +1,270 @@ +/* + * IPv6 Syncookies implementation for the Linux kernel + * + * Authors: + * Glenn Griffin <ggriffin.kernel@gmail.com> + * + * 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/siphash.h> +#include <linux/kernel.h> +#include <net/secure_seq.h> +#include <net/ipv6.h> +#include <net/tcp.h> + +#define COOKIEBITS 24 /* Upper bits store count */ +#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) + +static siphash_key_t syncookie6_secret[2] __read_mostly; + +/* RFC 2460, Section 8.3: + * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] + * + * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows + * using higher values than ipv4 tcp syncookies. + * The other values are chosen based on ethernet (1500 and 9k MTU), plus + * one that accounts for common encap (PPPoe) overhead. Table must be sorted. + */ +static __u16 const msstab[] = { + 1280 - 60, /* IPV6_MIN_MTU - 60 */ + 1480 - 60, + 1500 - 60, + 9000 - 60, +}; + +static u32 cookie_hash(const struct in6_addr *saddr, + const struct in6_addr *daddr, + __be16 sport, __be16 dport, u32 count, int c) +{ + const struct { + struct in6_addr saddr; + struct in6_addr daddr; + u32 count; + __be16 sport; + __be16 dport; + } __aligned(SIPHASH_ALIGNMENT) combined = { + .saddr = *saddr, + .daddr = *daddr, + .count = count, + .sport = sport, + .dport = dport + }; + + net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); + return siphash(&combined, offsetofend(typeof(combined), dport), + &syncookie6_secret[c]); +} + +static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, + const struct in6_addr *daddr, + __be16 sport, __be16 dport, __u32 sseq, + __u32 data) +{ + u32 count = tcp_cookie_time(); + 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, const struct in6_addr *saddr, + const struct in6_addr *daddr, __be16 sport, + __be16 dport, __u32 sseq) +{ + __u32 diff, count = tcp_cookie_time(); + + cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; + + diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); + if (diff >= MAX_SYNCOOKIE_AGE) + return (__u32)-1; + + return (cookie - + cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) + & COOKIEMASK; +} + +u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph, + const struct tcphdr *th, __u16 *mssp) +{ + int mssind; + const __u16 mss = *mssp; + + for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) + if (mss >= msstab[mssind]) + break; + + *mssp = msstab[mssind]; + + return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, + th->dest, ntohl(th->seq), mssind); +} +EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence); + +__u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp) +{ + const struct ipv6hdr *iph = ipv6_hdr(skb); + const struct tcphdr *th = tcp_hdr(skb); + + return __cookie_v6_init_sequence(iph, th, mssp); +} + +int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, + __u32 cookie) +{ + __u32 seq = ntohl(th->seq) - 1; + __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, + th->source, th->dest, seq); + + return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; +} +EXPORT_SYMBOL_GPL(__cookie_v6_check); + +struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_options_received tcp_opt; + struct inet_request_sock *ireq; + 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 full_space, mss; + struct dst_entry *dst; + __u8 rcv_wscale; + u32 tsoff = 0; + + if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst) + goto out; + + if (tcp_synq_no_recent_overflow(sk)) + goto out; + + mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); + if (mss == 0) { + __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); + goto out; + } + + __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); + + /* check for timestamp cookie support */ + memset(&tcp_opt, 0, sizeof(tcp_opt)); + tcp_parse_options(sock_net(sk), skb, &tcp_opt, 0, NULL); + + if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { + tsoff = secure_tcpv6_ts_off(sock_net(sk), + ipv6_hdr(skb)->daddr.s6_addr32, + ipv6_hdr(skb)->saddr.s6_addr32); + tcp_opt.rcv_tsecr -= tsoff; + } + + if (!cookie_timestamp_decode(sock_net(sk), &tcp_opt)) + goto out; + + ret = NULL; + req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false); + if (!req) + goto out; + + ireq = inet_rsk(req); + treq = tcp_rsk(req); + treq->af_specific = &tcp_request_sock_ipv6_ops; + treq->tfo_listener = false; + + if (security_inet_conn_request(sk, skb, req)) + goto out_free; + + req->mss = mss; + ireq->ir_rmt_port = th->source; + ireq->ir_num = ntohs(th->dest); + ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; + ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; + if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || + np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || + np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { + refcount_inc(&skb->users); + ireq->pktopts = skb; + } + + ireq->ir_iif = inet_request_bound_dev_if(sk, skb); + /* So that link locals have meaning */ + if (!sk->sk_bound_dev_if && + ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) + ireq->ir_iif = tcp_v6_iif(skb); + + ireq->ir_mark = inet_request_mark(sk, skb); + + req->num_retrans = 0; + ireq->snd_wscale = tcp_opt.snd_wscale; + ireq->sack_ok = tcp_opt.sack_ok; + ireq->wscale_ok = tcp_opt.wscale_ok; + ireq->tstamp_ok = tcp_opt.saw_tstamp; + req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; + treq->snt_synack = 0; + treq->rcv_isn = ntohl(th->seq) - 1; + treq->snt_isn = cookie; + treq->ts_off = 0; + treq->txhash = net_tx_rndhash(); + if (IS_ENABLED(CONFIG_SMC)) + ireq->smc_ok = 0; + + /* + * 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, final; + struct flowi6 fl6; + memset(&fl6, 0, sizeof(fl6)); + fl6.flowi6_proto = IPPROTO_TCP; + fl6.daddr = ireq->ir_v6_rmt_addr; + final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); + fl6.saddr = ireq->ir_v6_loc_addr; + fl6.flowi6_oif = ireq->ir_iif; + fl6.flowi6_mark = ireq->ir_mark; + fl6.fl6_dport = ireq->ir_rmt_port; + fl6.fl6_sport = inet_sk(sk)->inet_sport; + fl6.flowi6_uid = sk->sk_uid; + security_req_classify_flow(req, flowi6_to_flowi(&fl6)); + + dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p); + if (IS_ERR(dst)) + goto out_free; + } + + req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); + /* limit the window selection if the user enforce a smaller rx buffer */ + full_space = tcp_full_space(sk); + if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && + (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) + req->rsk_window_clamp = full_space; + + tcp_select_initial_window(sk, full_space, req->mss, + &req->rsk_rcv_wnd, &req->rsk_window_clamp, + ireq->wscale_ok, &rcv_wscale, + dst_metric(dst, RTAX_INITRWND)); + + ireq->rcv_wscale = rcv_wscale; + ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); + + ret = tcp_get_cookie_sock(sk, skb, req, dst, tsoff); +out: + return ret; +out_free: + reqsk_free(req); + return NULL; +} |