From 871480933a1c28f8a9fed4c4d34d06c439a7a422 Mon Sep 17 00:00:00 2001 From: Srikant Patnaik Date: Sun, 11 Jan 2015 12:28:04 +0530 Subject: Moved, renamed, and deleted files The original directory structure was scattered and unorganized. Changes are basically to make it look like kernel structure. --- net/ipv4/syncookies.c | 379 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 379 insertions(+) create mode 100644 net/ipv4/syncookies.c (limited to 'net/ipv4/syncookies.c') diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c new file mode 100644 index 00000000..eab2a7fb --- /dev/null +++ b/net/ipv4/syncookies.c @@ -0,0 +1,379 @@ +/* + * 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. + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +/* Timestamps: lowest bits store TCP options */ +#define TSBITS 6 +#define TSMASK (((__u32)1 << TSBITS) - 1) + +extern int sysctl_tcp_syncookies; + +__u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; +EXPORT_SYMBOL(syncookie_secret); + +static __init int init_syncookies(void) +{ + get_random_bytes(syncookie_secret, sizeof(syncookie_secret)); + return 0; +} +__initcall(init_syncookies); + +#define COOKIEBITS 24 /* Upper bits store count */ +#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) + +static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], + ipv4_cookie_scratch); + +static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, + u32 count, int c) +{ + __u32 *tmp = __get_cpu_var(ipv4_cookie_scratch); + + memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c])); + tmp[0] = (__force u32)saddr; + tmp[1] = (__force u32)daddr; + tmp[2] = ((__force u32)sport << 16) + (__force u32)dport; + tmp[3] = count; + sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); + + return tmp[17]; +} + + +/* + * when syncookies are in effect and tcp timestamps are enabled we encode + * tcp options in the lower bits of the timestamp value that will be + * sent in the syn-ack. + * Since subsequent timestamps use the normal tcp_time_stamp value, we + * must make sure that the resulting initial timestamp is <= tcp_time_stamp. + */ +__u32 cookie_init_timestamp(struct request_sock *req) +{ + struct inet_request_sock *ireq; + u32 ts, ts_now = tcp_time_stamp; + u32 options = 0; + + ireq = inet_rsk(req); + + options = ireq->wscale_ok ? ireq->snd_wscale : 0xf; + options |= ireq->sack_ok << 4; + options |= ireq->ecn_ok << 5; + + ts = ts_now & ~TSMASK; + ts |= options; + if (ts > ts_now) { + ts >>= TSBITS; + ts--; + ts <<= TSBITS; + ts |= options; + } + return ts; +} + + +static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, + __be16 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, __be32 saddr, __be32 daddr, + __be16 sport, __be16 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 */ +} + +/* + * MSS Values are taken from the 2009 paper + * 'Measuring TCP Maximum Segment Size' by S. Alcock and R. Nelson: + * - values 1440 to 1460 accounted for 80% of observed mss values + * - values outside the 536-1460 range are rare (<0.2%). + * + * Table must be sorted. + */ +static __u16 const msstab[] = { + 64, + 512, + 536, + 1024, + 1440, + 1460, + 4312, + 8960, +}; + +/* + * 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) +{ + const struct iphdr *iph = ip_hdr(skb); + const struct tcphdr *th = tcp_hdr(skb); + int mssind; + const __u16 mss = *mssp; + + tcp_synq_overflow(sk); + + for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) + if (mss >= msstab[mssind]) + break; + *mssp = msstab[mssind]; + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); + + return secure_tcp_syn_cookie(iph->saddr, iph->daddr, + th->source, th->dest, ntohl(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) +{ + const struct iphdr *iph = ip_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 < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; +} + +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; +} + + +/* + * when syncookies are in effect and tcp timestamps are enabled we stored + * additional tcp options in the timestamp. + * This extracts these options from the timestamp echo. + * + * The lowest 4 bits store snd_wscale. + * next 2 bits indicate SACK and ECN support. + * + * return false if we decode an option that should not be. + */ +bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, bool *ecn_ok) +{ + /* echoed timestamp, lowest bits contain options */ + u32 options = tcp_opt->rcv_tsecr & TSMASK; + + if (!tcp_opt->saw_tstamp) { + tcp_clear_options(tcp_opt); + return true; + } + + if (!sysctl_tcp_timestamps) + return false; + + tcp_opt->sack_ok = (options & (1 << 4)) ? TCP_SACK_SEEN : 0; + *ecn_ok = (options >> 5) & 1; + if (*ecn_ok && !sysctl_tcp_ecn) + return false; + + if (tcp_opt->sack_ok && !sysctl_tcp_sack) + return false; + + if ((options & 0xf) == 0xf) + return true; /* no window scaling */ + + tcp_opt->wscale_ok = 1; + tcp_opt->snd_wscale = options & 0xf; + return sysctl_tcp_window_scaling != 0; +} +EXPORT_SYMBOL(cookie_check_timestamp); + +struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, + struct ip_options *opt) +{ + struct tcp_options_received tcp_opt; + const u8 *hash_location; + struct inet_request_sock *ireq; + struct tcp_request_sock *treq; + 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 rtable *rt; + __u8 rcv_wscale; + bool ecn_ok = false; + struct flowi4 fl4; + + if (!sysctl_tcp_syncookies || !th->ack || th->rst) + goto out; + + if (tcp_synq_no_recent_overflow(sk) || + (mss = cookie_check(skb, cookie)) == 0) { + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); + goto out; + } + + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); + + /* check for timestamp cookie support */ + memset(&tcp_opt, 0, sizeof(tcp_opt)); + tcp_parse_options(skb, &tcp_opt, &hash_location, 0); + + if (!cookie_check_timestamp(&tcp_opt, &ecn_ok)) + goto out; + + ret = NULL; + req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */ + if (!req) + goto out; + + ireq = inet_rsk(req); + treq = tcp_rsk(req); + treq->rcv_isn = ntohl(th->seq) - 1; + treq->snt_isn = cookie; + req->mss = mss; + ireq->loc_port = th->dest; + ireq->rmt_port = th->source; + ireq->loc_addr = ip_hdr(skb)->daddr; + ireq->rmt_addr = ip_hdr(skb)->saddr; + ireq->ecn_ok = ecn_ok; + 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 = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; + + /* 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_rcu) + opt->optlen; + + ireq->opt = kmalloc(opt_size, GFP_ATOMIC); + if (ireq->opt != NULL && ip_options_echo(&ireq->opt->opt, skb)) { + kfree(ireq->opt); + ireq->opt = NULL; + } + } + + if (security_inet_conn_request(sk, skb, req)) { + reqsk_free(req); + goto out; + } + + 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. + */ + flowi4_init_output(&fl4, 0, sk->sk_mark, RT_CONN_FLAGS(sk), + RT_SCOPE_UNIVERSE, IPPROTO_TCP, + inet_sk_flowi_flags(sk), + (opt && opt->srr) ? opt->faddr : ireq->rmt_addr, + ireq->loc_addr, th->source, th->dest); + security_req_classify_flow(req, flowi4_to_flowi(&fl4)); + rt = ip_route_output_key(sock_net(sk), &fl4); + if (IS_ERR(rt)) { + reqsk_free(req); + goto out; + } + + /* Try to redo what tcp_v4_send_synack did. */ + req->window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW); + + tcp_select_initial_window(tcp_full_space(sk), req->mss, + &req->rcv_wnd, &req->window_clamp, + ireq->wscale_ok, &rcv_wscale, + dst_metric(&rt->dst, RTAX_INITRWND)); + + ireq->rcv_wscale = rcv_wscale; + + ret = get_cookie_sock(sk, skb, req, &rt->dst); + /* ip_queue_xmit() depends on our flow being setup + * Normal sockets get it right from inet_csk_route_child_sock() + */ + if (ret) + inet_sk(ret)->cork.fl.u.ip4 = fl4; +out: return ret; +} -- cgit