[PATCH v3 15/16] tcp: "TCP" hash secret doesn't need to be TCP specific

[David Gibson <david@gibson.dropbear.id.au>]

The TCP state structure includes a 128-bit hash_secret which we use for
SipHash calculations to mitigate attacks on the TCP hash table and initial
sequence number.

We have plans to use SipHash in places that aren't TCP related, and there's
no particular reason they'd need their own secret.  So move the hash_secret
to the general context structure.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 passt.c | 40 ++++++++++++++++++++++++++++++++++++++++
 passt.h |  2 ++
 tcp.c   | 35 ++---------------------------------
 tcp.h   |  2 --
 4 files changed, 44 insertions(+), 35 deletions(-)

diff --git a/passt.c b/passt.c
index 8ddd9b3..0246b04 100644
--- a/passt.c
+++ b/passt.c
@@ -35,6 +35,9 @@
 #include <syslog.h>
 #include <sys/prctl.h>
 #include <netinet/if_ether.h>
+#ifdef HAS_GETRANDOM
+#include <sys/random.h>
+#endif
 
 #include "util.h"
 #include "passt.h"
@@ -103,6 +106,41 @@ static void post_handler(struct ctx *c, const struct timespec *now)
 #undef CALL_PROTO_HANDLER
 }
 
+/**
+ * secret_init() - Create secret value for SipHash calculations
+ * @c:		Execution context
+ */
+static void secret_init(struct ctx *c)
+{
+#ifndef HAS_GETRANDOM
+	int dev_random = open("/dev/random", O_RDONLY);
+	unsigned int random_read = 0;
+
+	while (dev_random && random_read < sizeof(c->hash_secret)) {
+		int ret = read(dev_random,
+			       (uint8_t *)&c->hash_secret + random_read,
+			       sizeof(c->hash_secret) - random_read);
+
+		if (ret == -1 && errno == EINTR)
+			continue;
+
+		if (ret <= 0)
+			break;
+
+		random_read += ret;
+	}
+	if (dev_random >= 0)
+		close(dev_random);
+	if (random_read < sizeof(c->hash_secret)) {
+#else
+	if (getrandom(&c->hash_secret, sizeof(c->hash_secret),
+		      GRND_RANDOM) < 0) {
+#endif /* !HAS_GETRANDOM */
+		perror("TCP initial sequence getrandom");
+		exit(EXIT_FAILURE);
+	}
+}
+
 /**
  * timer_init() - Set initial timestamp for timer runs to current time
  * @c:		Execution context
@@ -237,6 +275,8 @@ int main(int argc, char **argv)
 
 	tap_sock_init(&c);
 
+	secret_init(&c);
+
 	clock_gettime(CLOCK_MONOTONIC, &now);
 
 	if ((!c.no_udp && udp_init(&c)) || (!c.no_tcp && tcp_init(&c)))
diff --git a/passt.h b/passt.h
index 33b493f..c74887a 100644
--- a/passt.h
+++ b/passt.h
@@ -211,6 +211,7 @@ struct ip6_ctx {
  * @fd_tap:		AF_UNIX socket, tuntap device, or pre-opened socket
  * @mac:		Host MAC address
  * @mac_guest:		MAC address of guest or namespace, seen or configured
+ * @hash_secret:	128-bit secret for siphash functions
  * @ifi4:		Index of template interface for IPv4, 0 if IPv4 disabled
  * @ip:			IPv4 configuration
  * @dns_search:		DNS search list
@@ -265,6 +266,7 @@ struct ctx {
 	int fd_tap;
 	unsigned char mac[ETH_ALEN];
 	unsigned char mac_guest[ETH_ALEN];
+	uint64_t hash_secret[2];
 
 	unsigned int ifi4;
 	struct ip4_ctx ip4;
diff --git a/tcp.c b/tcp.c
index 24aba44..74d06bf 100644
--- a/tcp.c
+++ b/tcp.c
@@ -279,9 +279,6 @@
 #include <stddef.h>
 #include <string.h>
 #include <sys/epoll.h>
-#ifdef HAS_GETRANDOM
-#include <sys/random.h>
-#endif
 #include <sys/socket.h>
 #include <sys/timerfd.h>
 #include <sys/types.h>
@@ -1172,7 +1169,7 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
 static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr,
 			     in_port_t eport, in_port_t fport)
 {
-	struct siphash_state state = SIPHASH_INIT(c->tcp.hash_secret);
+	struct siphash_state state = SIPHASH_INIT(c->hash_secret);
 	uint64_t hash;
 
 	inany_siphash_feed(&state, faddr);
@@ -1780,7 +1777,7 @@ static void tcp_tap_window_update(struct tcp_tap_conn *conn, unsigned wnd)
 static void tcp_seq_init(const struct ctx *c, struct tcp_tap_conn *conn,
 			 const struct timespec *now)
 {
-	struct siphash_state state = SIPHASH_INIT(c->tcp.hash_secret);
+	struct siphash_state state = SIPHASH_INIT(c->hash_secret);
 	union inany_addr aany;
 	uint64_t hash;
 	uint32_t ns;
@@ -3088,34 +3085,6 @@ static void tcp_sock_refill_init(const struct ctx *c)
  */
 int tcp_init(struct ctx *c)
 {
-#ifndef HAS_GETRANDOM
-	int dev_random = open("/dev/random", O_RDONLY);
-	unsigned int random_read = 0;
-
-	while (dev_random && random_read < sizeof(c->tcp.hash_secret)) {
-		int ret = read(dev_random,
-			       (uint8_t *)&c->tcp.hash_secret + random_read,
-			       sizeof(c->tcp.hash_secret) - random_read);
-
-		if (ret == -1 && errno == EINTR)
-			continue;
-
-		if (ret <= 0)
-			break;
-
-		random_read += ret;
-	}
-	if (dev_random >= 0)
-		close(dev_random);
-	if (random_read < sizeof(c->tcp.hash_secret)) {
-#else
-	if (getrandom(&c->tcp.hash_secret, sizeof(c->tcp.hash_secret),
-		      GRND_RANDOM) < 0) {
-#endif /* !HAS_GETRANDOM */
-		perror("TCP initial sequence getrandom");
-		exit(EXIT_FAILURE);
-	}
-
 	if (c->ifi4)
 		tcp_sock4_iov_init(c);
 
diff --git a/tcp.h b/tcp.h
index c8b738d..27b1166 100644
--- a/tcp.h
+++ b/tcp.h
@@ -52,7 +52,6 @@ union tcp_listen_epoll_ref {
 
 /**
  * struct tcp_ctx - Execution context for TCP routines
- * @hash_secret:	128-bit secret for hash functions, ISN and hash table
  * @port_to_tap:	Ports bound host-side, packets to tap or spliced
  * @fwd_in:		Port forwarding configuration for inbound packets
  * @fwd_out:		Port forwarding configuration for outbound packets
@@ -61,7 +60,6 @@ union tcp_listen_epoll_ref {
  * @pipe_size:		Size of pipes for spliced connections
  */
 struct tcp_ctx {
-	uint64_t hash_secret[2];
 	struct port_fwd fwd_in;
 	struct port_fwd fwd_out;
 	struct timespec timer_run;
-- 
@@ -52,7 +52,6 @@ union tcp_listen_epoll_ref {
 
 /**
  * struct tcp_ctx - Execution context for TCP routines
- * @hash_secret:	128-bit secret for hash functions, ISN and hash table
  * @port_to_tap:	Ports bound host-side, packets to tap or spliced
  * @fwd_in:		Port forwarding configuration for inbound packets
  * @fwd_out:		Port forwarding configuration for outbound packets
@@ -61,7 +60,6 @@ union tcp_listen_epoll_ref {
  * @pipe_size:		Size of pipes for spliced connections
  */
 struct tcp_ctx {
-	uint64_t hash_secret[2];
 	struct port_fwd fwd_in;
 	struct port_fwd fwd_out;
 	struct timespec timer_run;
-- 
2.43.0