1 files changed, 84 insertions, 5 deletions

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index abc752d45cf7..73ba98921d64 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -19,6 +19,10 @@
 #include <linux/kernel.h>
 #include <net/tcp.h>
 
+/* Timestamps: lowest 9 bits store TCP options */
+#define TSBITS 9
+#define TSMASK (((__u32)1 << TSBITS) - 1)
+
 extern int sysctl_tcp_syncookies;
 
 __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
@@ -51,6 +55,39 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
         return tmp[17];
 }
 
+
+/*
+ * when syncookies are in effect and tcp timestamps are enabled we encode
+ * tcp options in the lowest 9 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);
+        if (ireq->wscale_ok) {
+                options = ireq->snd_wscale;
+                options |= ireq->rcv_wscale << 4;
+        }
+        options |= ireq->sack_ok << 8;
+
+        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)
@@ -185,6 +222,35 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
         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 are for snd_wscale
+ * The next 4 lsb are for rcv_wscale
+ * The next lsb is for sack_ok
+ */
+void cookie_check_timestamp(struct tcp_options_received *tcp_opt)
+{
+        /* echoed timestamp, 9 lowest bits contain options */
+        u32 options = tcp_opt->rcv_tsecr & TSMASK;
+
+        tcp_opt->snd_wscale = options & 0xf;
+        options >>= 4;
+        tcp_opt->rcv_wscale = options & 0xf;
+
+        tcp_opt->sack_ok = (options >> 4) & 0x1;
+
+        if (tcp_opt->sack_ok)
+                tcp_sack_reset(tcp_opt);
+
+        if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)
+                tcp_opt->wscale_ok = 1;
+}
+EXPORT_SYMBOL(cookie_check_timestamp);
+
 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
                              struct ip_options *opt)
 {
@@ -198,6 +264,7 @@ 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;
@@ -210,6 +277,13 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
 
         NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV);
 
+        /* check for timestamp cookie support */
+        memset(&tcp_opt, 0, sizeof(tcp_opt));
+        tcp_parse_options(skb, &tcp_opt, 0);
+
+        if (tcp_opt.saw_tstamp)
+                cookie_check_timestamp(&tcp_opt);
+
         ret = NULL;
         req = reqsk_alloc(&tcp_request_sock_ops); /* for safety */
         if (!req)
@@ -228,6 +302,12 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         ireq->loc_addr          = ip_hdr(skb)->daddr;
         ireq->rmt_addr          = ip_hdr(skb)->saddr;
         ireq->opt               = NULL;
+        ireq->snd_wscale        = tcp_opt.snd_wscale;
+        ireq->rcv_wscale        = tcp_opt.rcv_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;
 
         /* 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)
@@ -242,8 +322,6 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
                 }
         }
 
-        ireq->snd_wscale = ireq->rcv_wscale = ireq->tstamp_ok = 0;
-        ireq->wscale_ok  = ireq->sack_ok = 0;
         req->expires    = 0UL;
         req->retrans    = 0;
 
@@ -272,11 +350,12 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
         }
 
         /* Try to redo what tcp_v4_send_synack did. */
-        req->window_clamp = dst_metric(&rt->u.dst, RTAX_WINDOW);
+        req->window_clamp = tp->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->wscale_ok, &rcv_wscale);
+
         ireq->rcv_wscale  = rcv_wscale;
 
         ret = get_cookie_sock(sk, skb, req, &rt->u.dst);