TCPCT part 1g: Responder Cookie => Initiator

Parse incoming TCP_COOKIE option(s).

Calculate <SYN,ACK> TCP_COOKIE option.

Send optional <SYN,ACK> data.

This is a significantly revised implementation of an earlier (year-old)
patch that no longer applies cleanly, with permission of the original
author (Adam Langley):

    http://thread.gmane.org/gmane.linux.network/102586

Requires:
   TCPCT part 1a: add request_values parameter for sending SYNACK
   TCPCT part 1b: generate Responder Cookie secret
   TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS
   TCPCT part 1d: define TCP cookie option, extend existing struct's
   TCPCT part 1e: implement socket option TCP_COOKIE_TRANSACTIONS
   TCPCT part 1f: Initiator Cookie => Responder

Signed-off-by: William.Allen.Simpson@gmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 205 insertions, 39 deletions

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 3146cc401748..26399ad2a289 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -253,6 +253,8 @@ 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;
+        u8 *hash_location;
         struct inet_request_sock *ireq;
         struct tcp_request_sock *treq;
         struct tcp_sock *tp = tcp_sk(sk);
@@ -263,7 +265,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         int mss;
         struct rtable *rt;
         __u8 rcv_wscale;
-        struct tcp_options_received tcp_opt;
 
         if (!sysctl_tcp_syncookies || !th->ack)
                 goto out;
@@ -341,7 +342,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
 
         /* check for timestamp cookie support */
         memset(&tcp_opt, 0, sizeof(tcp_opt));
-        tcp_parse_options(skb, &tcp_opt, 0, &rt->u.dst);
+        tcp_parse_options(skb, &tcp_opt, &hash_location, 0, &rt->u.dst);
 
         if (tcp_opt.saw_tstamp)
                 cookie_check_timestamp(&tcp_opt);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index be166e0e11c5..57ae96a04220 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3698,7 +3698,7 @@ old_ack:
  * the fast version below fails.
  */
 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
-                       int estab,  struct dst_entry *dst)
+                       u8 **hvpp, int estab,  struct dst_entry *dst)
 {
         unsigned char *ptr;
         struct tcphdr *th = tcp_hdr(skb);
@@ -3785,7 +3785,30 @@ void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
                                  */
                                 break;
 #endif
-                        }
+                        case TCPOPT_COOKIE:
+                                /* This option is variable length.
+                                 */
+                                switch (opsize) {
+                                case TCPOLEN_COOKIE_BASE:
+                                        /* not yet implemented */
+                                        break;
+                                case TCPOLEN_COOKIE_PAIR:
+                                        /* not yet implemented */
+                                        break;
+                                case TCPOLEN_COOKIE_MIN+0:
+                                case TCPOLEN_COOKIE_MIN+2:
+                                case TCPOLEN_COOKIE_MIN+4:
+                                case TCPOLEN_COOKIE_MIN+6:
+                                case TCPOLEN_COOKIE_MAX:
+                                        /* 16-bit multiple */
+                                        opt_rx->cookie_plus = opsize;
+                                        *hvpp = ptr;
+                                default:
+                                        /* ignore option */
+                                        break;
+                                };
+                                break;
+                        };
 
                         ptr += opsize-2;
                         length -= opsize;
@@ -3813,17 +3836,20 @@ static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
  * If it is wrong it falls back on tcp_parse_options().
  */
 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
-                                  struct tcp_sock *tp)
+                                  struct tcp_sock *tp, u8 **hvpp)
 {
-        if (th->doff == sizeof(struct tcphdr) >> 2) {
+        /* In the spirit of fast parsing, compare doff directly to constant
+         * values.  Because equality is used, short doff can be ignored here.
+         */
+        if (th->doff == (sizeof(*th) / 4)) {
                 tp->rx_opt.saw_tstamp = 0;
                 return 0;
         } else if (tp->rx_opt.tstamp_ok &&
-                   th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
+                   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
                 if (tcp_parse_aligned_timestamp(tp, th))
                         return 1;
         }
-        tcp_parse_options(skb, &tp->rx_opt, 1, NULL);
+        tcp_parse_options(skb, &tp->rx_opt, hvpp, 1, NULL);
         return 1;
 }
 
@@ -5077,10 +5103,12 @@ out:
 static int tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
                               struct tcphdr *th, int syn_inerr)
 {
+        u8 *hash_location;
         struct tcp_sock *tp = tcp_sk(sk);
 
         /* RFC1323: H1. Apply PAWS check first. */
-        if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
+        if (tcp_fast_parse_options(skb, th, tp, &hash_location) &&
+            tp->rx_opt.saw_tstamp &&
             tcp_paws_discard(sk, skb)) {
                 if (!th->rst) {
                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
@@ -5368,12 +5396,14 @@ discard:
 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
                                          struct tcphdr *th, unsigned len)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
+        u8 *hash_location;
         struct inet_connection_sock *icsk = inet_csk(sk);
-        int saved_clamp = tp->rx_opt.mss_clamp;
+        struct tcp_sock *tp = tcp_sk(sk);
         struct dst_entry *dst = __sk_dst_get(sk);
+        struct tcp_cookie_values *cvp = tp->cookie_values;
+        int saved_clamp = tp->rx_opt.mss_clamp;
 
-        tcp_parse_options(skb, &tp->rx_opt, 0, dst);
+        tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0, dst);
 
         if (th->ack) {
                 /* rfc793:
@@ -5470,6 +5500,31 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
                  * Change state from SYN-SENT only after copied_seq
                  * is initialized. */
                 tp->copied_seq = tp->rcv_nxt;
+
+                if (cvp != NULL &&
+                    cvp->cookie_pair_size > 0 &&
+                    tp->rx_opt.cookie_plus > 0) {
+                        int cookie_size = tp->rx_opt.cookie_plus
+                                        - TCPOLEN_COOKIE_BASE;
+                        int cookie_pair_size = cookie_size
+                                             + cvp->cookie_desired;
+
+                        /* A cookie extension option was sent and returned.
+                         * Note that each incoming SYNACK replaces the
+                         * Responder cookie.  The initial exchange is most
+                         * fragile, as protection against spoofing relies
+                         * entirely upon the sequence and timestamp (above).
+                         * This replacement strategy allows the correct pair to
+                         * pass through, while any others will be filtered via
+                         * Responder verification later.
+                         */
+                        if (sizeof(cvp->cookie_pair) >= cookie_pair_size) {
+                                memcpy(&cvp->cookie_pair[cvp->cookie_desired],
+                                       hash_location, cookie_size);
+                                cvp->cookie_pair_size = cookie_pair_size;
+                        }
+                }
+
                 smp_mb();
                 tcp_set_state(sk, TCP_ESTABLISHED);
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a2bcac9b388e..59c911f3889d 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1213,9 +1213,12 @@ static struct timewait_sock_ops tcp_timewait_sock_ops = {
 
 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 {
+        struct tcp_extend_values tmp_ext;
         struct tcp_options_received tmp_opt;
+        u8 *hash_location;
         struct request_sock *req;
         struct inet_request_sock *ireq;
+        struct tcp_sock *tp = tcp_sk(sk);
         struct dst_entry *dst = NULL;
         __be32 saddr = ip_hdr(skb)->saddr;
         __be32 daddr = ip_hdr(skb)->daddr;
@@ -1271,15 +1274,49 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 
         tcp_clear_options(&tmp_opt);
         tmp_opt.mss_clamp = TCP_MSS_DEFAULT;
-        tmp_opt.user_mss  = tcp_sk(sk)->rx_opt.user_mss;
+        tmp_opt.user_mss  = tp->rx_opt.user_mss;
+        tcp_parse_options(skb, &tmp_opt, &hash_location, 0, dst);
+
+        if (tmp_opt.cookie_plus > 0 &&
+            tmp_opt.saw_tstamp &&
+            !tp->rx_opt.cookie_out_never &&
+            (sysctl_tcp_cookie_size > 0 ||
+             (tp->cookie_values != NULL &&
+              tp->cookie_values->cookie_desired > 0))) {
+                u8 *c;
+                u32 *mess = &tmp_ext.cookie_bakery[COOKIE_DIGEST_WORDS];
+                int l = tmp_opt.cookie_plus - TCPOLEN_COOKIE_BASE;
+
+                if (tcp_cookie_generator(&tmp_ext.cookie_bakery[0]) != 0)
+                        goto drop_and_release;
+
+                /* Secret recipe starts with IP addresses */
+                *mess++ ^= daddr;
+                *mess++ ^= saddr;
 
-        tcp_parse_options(skb, &tmp_opt, 0, dst);
+                /* plus variable length Initiator Cookie */
+                c = (u8 *)mess;
+                while (l-- > 0)
+                        *c++ ^= *hash_location++;
+
+#ifdef CONFIG_SYN_COOKIES
+                want_cookie = 0;        /* not our kind of cookie */
+#endif
+                tmp_ext.cookie_out_never = 0; /* false */
+                tmp_ext.cookie_plus = tmp_opt.cookie_plus;
+        } else if (!tp->rx_opt.cookie_in_always) {
+                /* redundant indications, but ensure initialization. */
+                tmp_ext.cookie_out_never = 1; /* true */
+                tmp_ext.cookie_plus = 0;
+        } else {
+                goto drop_and_release;
+        }
+        tmp_ext.cookie_in_always = tp->rx_opt.cookie_in_always;
 
         if (want_cookie && !tmp_opt.saw_tstamp)
                 tcp_clear_options(&tmp_opt);
 
         tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
-
         tcp_openreq_init(req, &tmp_opt, skb);
 
         if (security_inet_conn_request(sk, skb, req))
@@ -1339,7 +1376,9 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
         }
         tcp_rsk(req)->snt_isn = isn;
 
-        if (__tcp_v4_send_synack(sk, dst, req, NULL) || want_cookie)
+        if (__tcp_v4_send_synack(sk, dst, req,
+                                 (struct request_values *)&tmp_ext) ||
+            want_cookie)
                 goto drop_and_free;
 
         inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 96852af43ca7..87accec8d097 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -90,13 +90,14 @@ enum tcp_tw_status
 tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
                            const struct tcphdr *th)
 {
-        struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
         struct tcp_options_received tmp_opt;
+        u8 *hash_location;
+        struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
         int paws_reject = 0;
 
         if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
                 tmp_opt.tstamp_ok = 1;
-                tcp_parse_options(skb, &tmp_opt, 1, NULL);
+                tcp_parse_options(skb, &tmp_opt, &hash_location, 1, NULL);
 
                 if (tmp_opt.saw_tstamp) {
                         tmp_opt.ts_recent       = tcptw->tw_ts_recent;
@@ -518,15 +519,16 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
                            struct request_sock *req,
                            struct request_sock **prev)
 {
+        struct tcp_options_received tmp_opt;
+        u8 *hash_location;
+        struct sock *child;
         const struct tcphdr *th = tcp_hdr(skb);
         __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK);
         int paws_reject = 0;
-        struct tcp_options_received tmp_opt;
-        struct sock *child;
 
-        if ((th->doff > (sizeof(struct tcphdr)>>2)) && (req->ts_recent)) {
+        if ((th->doff > (sizeof(*th) >> 2)) && (req->ts_recent)) {
                 tmp_opt.tstamp_ok = 1;
-                tcp_parse_options(skb, &tmp_opt, 1, NULL);
+                tcp_parse_options(skb, &tmp_opt, &hash_location, 1, NULL);
 
                 if (tmp_opt.saw_tstamp) {
                         tmp_opt.ts_recent = req->ts_recent;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 35dd983a8a99..2ac8beff4d77 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -655,48 +655,77 @@ static unsigned tcp_synack_options(struct sock *sk,
                                    struct request_sock *req,
                                    unsigned mss, struct sk_buff *skb,
                                    struct tcp_out_options *opts,
-                                   struct tcp_md5sig_key **md5) {
-        unsigned size = 0;
+                                   struct tcp_md5sig_key **md5,
+                                   struct tcp_extend_values *xvp)
+{
         struct inet_request_sock *ireq = inet_rsk(req);
-        char doing_ts;
+        unsigned remaining = MAX_TCP_OPTION_SPACE;
+        u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
+                         xvp->cookie_plus :
+                         0;
+        bool doing_ts = ireq->tstamp_ok;
 
 #ifdef CONFIG_TCP_MD5SIG
         *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
         if (*md5) {
                 opts->options |= OPTION_MD5;
-                size += TCPOLEN_MD5SIG_ALIGNED;
+                remaining -= TCPOLEN_MD5SIG_ALIGNED;
+
+                /* We can't fit any SACK blocks in a packet with MD5 + TS
+                 * options. There was discussion about disabling SACK
+                 * rather than TS in order to fit in better with old,
+                 * buggy kernels, but that was deemed to be unnecessary.
+                 */
+                doing_ts &= !ireq->sack_ok;
         }
 #else
         *md5 = NULL;
 #endif
 
-        /* we can't fit any SACK blocks in a packet with MD5 + TS
-           options. There was discussion about disabling SACK rather than TS in
-           order to fit in better with old, buggy kernels, but that was deemed
-           to be unnecessary. */
-        doing_ts = ireq->tstamp_ok && !(*md5 && ireq->sack_ok);
-
+        /* We always send an MSS option. */
         opts->mss = mss;
-        size += TCPOLEN_MSS_ALIGNED;
+        remaining -= TCPOLEN_MSS_ALIGNED;
 
         if (likely(ireq->wscale_ok)) {
                 opts->ws = ireq->rcv_wscale;
                 opts->options |= OPTION_WSCALE;
-                size += TCPOLEN_WSCALE_ALIGNED;
+                remaining -= TCPOLEN_WSCALE_ALIGNED;
         }
         if (likely(doing_ts)) {
                 opts->options |= OPTION_TS;
                 opts->tsval = TCP_SKB_CB(skb)->when;
                 opts->tsecr = req->ts_recent;
-                size += TCPOLEN_TSTAMP_ALIGNED;
+                remaining -= TCPOLEN_TSTAMP_ALIGNED;
         }
         if (likely(ireq->sack_ok)) {
                 opts->options |= OPTION_SACK_ADVERTISE;
                 if (unlikely(!doing_ts))
-                        size += TCPOLEN_SACKPERM_ALIGNED;
+                        remaining -= TCPOLEN_SACKPERM_ALIGNED;
         }
 
-        return size;
+        /* Similar rationale to tcp_syn_options() applies here, too.
+         * If the <SYN> options fit, the same options should fit now!
+         */
+        if (*md5 == NULL &&
+            doing_ts &&
+            cookie_plus > TCPOLEN_COOKIE_BASE) {
+                int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */
+
+                if (0x2 & need) {
+                        /* 32-bit multiple */
+                        need += 2; /* NOPs */
+                }
+                if (need <= remaining) {
+                        opts->options |= OPTION_COOKIE_EXTENSION;
+                        opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE;
+                        remaining -= need;
+                } else {
+                        /* There's no error return, so flag it. */
+                        xvp->cookie_out_never = 1; /* true */
+                        opts->hash_size = 0;
+                }
+        }
+        return MAX_TCP_OPTION_SPACE - remaining;
 }
 
 /* Compute TCP options for ESTABLISHED sockets. This is not the
@@ -2365,6 +2394,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
                                 struct request_values *rvp)
 {
         struct tcp_out_options opts;
+        struct tcp_extend_values *xvp = tcp_xv(rvp);
         struct inet_request_sock *ireq = inet_rsk(req);
         struct tcp_sock *tp = tcp_sk(sk);
         struct tcphdr *th;
@@ -2408,8 +2438,8 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
 #endif
         TCP_SKB_CB(skb)->when = tcp_time_stamp;
         tcp_header_size = tcp_synack_options(sk, req, mss,
-                                             skb, &opts, &md5) +
-                          sizeof(struct tcphdr);
+                                             skb, &opts, &md5, xvp)
+                        + sizeof(*th);
 
         skb_push(skb, tcp_header_size);
         skb_reset_transport_header(skb);
@@ -2426,6 +2456,45 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
          */
         tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
                              TCPCB_FLAG_SYN | TCPCB_FLAG_ACK);
+
+        if (OPTION_COOKIE_EXTENSION & opts.options) {
+                const struct tcp_cookie_values *cvp = tp->cookie_values;
+
+                if (cvp != NULL &&
+                    cvp->s_data_constant &&
+                    cvp->s_data_desired > 0) {
+                        u8 *buf = skb_put(skb, cvp->s_data_desired);
+
+                        /* copy data directly from the listening socket. */
+                        memcpy(buf, cvp->s_data_payload, cvp->s_data_desired);
+                        TCP_SKB_CB(skb)->end_seq += cvp->s_data_desired;
+                }
+
+                if (opts.hash_size > 0) {
+                        __u32 workspace[SHA_WORKSPACE_WORDS];
+                        u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS];
+                        u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1];
+
+                        /* Secret recipe depends on the Timestamp, (future)
+                         * Sequence and Acknowledgment Numbers, Initiator
+                         * Cookie, and others handled by IP variant caller.
+                         */
+                        *tail-- ^= opts.tsval;
+                        *tail-- ^= tcp_rsk(req)->rcv_isn + 1;
+                        *tail-- ^= TCP_SKB_CB(skb)->seq + 1;
+
+                        /* recommended */
+                        *tail-- ^= ((th->dest << 16) | th->source);
+                        *tail-- ^= (u32)cvp; /* per sockopt */
+
+                        sha_transform((__u32 *)&xvp->cookie_bakery[0],
+                                      (char *)mess,
+                                      &workspace[0]);
+                        opts.hash_location =
+                                (__u8 *)&xvp->cookie_bakery[0];
+                }
+        }
+
         th->seq = htonl(TCP_SKB_CB(skb)->seq);
         th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);