Randomize the TCP initial sequence numbers more thoroughly.

Obtained from:	OpenBSD
Reviewed by:	jesper, peter, -developers

1 files changed, 61 insertions, 1 deletions

diff --git a/sys/netinet/tcp_timewait.c b/sys/netinet/tcp_timewait.c
index 2afff53..64f4c06 100644
--- a/sys/netinet/tcp_timewait.c
+++ b/sys/netinet/tcp_timewait.c
@@ -53,6 +53,7 @@
 #include <sys/socket.h>
 #include <sys/socketvar.h>
 #include <sys/protosw.h>
+#include <sys/random.h>
 
 #include <vm/vm_zone.h>
 
@@ -181,7 +182,9 @@ tcp_init()
 {
 	int hashsize;
 	
-	tcp_iss = arc4random();	/* wrong, but better than a constant */
+#ifdef TCP_COMPAT_42
+	tcp_iss = 1;		/* wrong */
+#endif /* TCP_COMPAT_42 */
 	tcp_ccgen = 1;
 	tcp_cleartaocache();
 
@@ -1100,6 +1103,63 @@ tcp6_ctlinput(cmd, sa, d)
 }
 #endif /* INET6 */
 
+#define TCP_RNDISS_ROUNDS	16
+#define TCP_RNDISS_OUT	7200
+#define TCP_RNDISS_MAX	30000
+
+u_int8_t tcp_rndiss_sbox[128];
+u_int16_t tcp_rndiss_msb;
+u_int16_t tcp_rndiss_cnt;
+long tcp_rndiss_reseed;
+
+u_int16_t
+tcp_rndiss_encrypt(val)
+	u_int16_t val;
+{
+	u_int16_t sum = 0, i;
+  
+	for (i = 0; i < TCP_RNDISS_ROUNDS; i++) {
+		sum += 0x79b9;
+		val ^= ((u_int16_t)tcp_rndiss_sbox[(val^sum) & 0x7f]) << 7;
+		val = ((val & 0xff) << 7) | (val >> 8);
+	}
+
+	return val;
+}
+
+void
+tcp_rndiss_init()
+{
+	struct timeval time;
+
+	getmicrotime(&time);
+	read_random(tcp_rndiss_sbox, sizeof(tcp_rndiss_sbox));
+
+	tcp_rndiss_reseed = time.tv_sec + TCP_RNDISS_OUT;
+	tcp_rndiss_msb = tcp_rndiss_msb == 0x8000 ? 0 : 0x8000; 
+	tcp_rndiss_cnt = 0;
+}
+
+tcp_seq
+tcp_rndiss_next()
+{
+	u_int16_t tmp;
+	struct timeval time;
+
+	getmicrotime(&time);
+
+        if (tcp_rndiss_cnt >= TCP_RNDISS_MAX ||
+	    time.tv_sec > tcp_rndiss_reseed)
+                tcp_rndiss_init();
+	
+	read_random(&tmp, sizeof(tmp));
+
+	/* (tmp & 0x7fff) ensures a 32768 byte gap between ISS */
+	return ((tcp_rndiss_encrypt(tcp_rndiss_cnt++) | tcp_rndiss_msb) <<16) |
+		(tmp & 0x7fff);
+}
+
+
 /*
  * When a source quench is received, close congestion window
  * to one segment.  We will gradually open it again as we proceed.