tcp: Better helpers for converting between connection pointer and index

The macro CONN_OR_NULL() is used to look up connections by index with
bounds checking.  Replace it with an inline function, which means:
    - Better type checking
    - No danger of multiple evaluation of an @index with side effects

Also add a helper to perform the reverse translation: from connection
pointer to index.  Introduce a macro for this which will make later
cleanups easier and safer.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 45 insertions, 38 deletions

diff --git a/tcp.c b/tcp.c
index d043123..34d7d45 100644
--- a/tcp.c
+++ b/tcp.c
@@ -518,14 +518,6 @@ struct tcp_conn {
 	 (conn->events & (SOCK_FIN_RCVD | TAP_FIN_RCVD)))
 #define CONN_HAS(conn, set)	((conn->events & (set)) == (set))
 
-#define CONN(index)		(tc + (index))
-
-/* We probably don't want to use gcc statement expressions (for portability), so
- * use this only after well-defined sequence points (no pre-/post-increments).
- */
-#define CONN_OR_NULL(index)						\
-	(((int)(index) >= 0 && (index) < TCP_MAX_CONNS) ? (tc + (index)) : NULL)
-
 static const char *tcp_event_str[] __attribute((__unused__)) = {
 	"SOCK_ACCEPTED", "TAP_SYN_RCVD", "ESTABLISHED", "TAP_SYN_ACK_SENT",
 
@@ -705,6 +697,21 @@ static size_t tcp6_l2_flags_buf_bytes;
 /* TCP connections */
 static struct tcp_conn tc[TCP_MAX_CONNS];
 
+#define CONN(index)		(tc + (index))
+#define CONN_IDX(conn)		((conn) - tc)
+
+/** conn_at_idx() - Find a connection by index, if present
+ * @index:	Index of connection to lookup
+ *
+ * Return: pointer to connection, or NULL if @index is out of bounds
+ */
+static inline struct tcp_conn *conn_at_idx(int index)
+{
+	if ((index < 0) || (index >= TCP_MAX_CONNS))
+		return NULL;
+	return CONN(index);
+}
+
 /* Table for lookup from remote address, local port, remote port */
 static struct tcp_conn *tc_hash[TCP_HASH_TABLE_SIZE];
 
@@ -761,7 +768,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_conn *conn)
 {
 	int m = (conn->flags & IN_EPOLL) ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref = { .r.proto = IPPROTO_TCP, .r.s = conn->sock,
-				.r.p.tcp.tcp.index = conn - tc,
+				.r.p.tcp.tcp.index = CONN_IDX(conn),
 				.r.p.tcp.tcp.v6 = CONN_V6(conn) };
 	struct epoll_event ev = { .data.u64 = ref.u64 };
 
@@ -784,7 +791,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_conn *conn)
 		union epoll_ref ref_t = { .r.proto = IPPROTO_TCP,
 					  .r.s = conn->sock,
 					  .r.p.tcp.tcp.timer = 1,
-					  .r.p.tcp.tcp.index = conn - tc };
+					  .r.p.tcp.tcp.index = CONN_IDX(conn) };
 		struct epoll_event ev_t = { .data.u64 = ref_t.u64,
 					    .events = EPOLLIN | EPOLLET };
 
@@ -813,7 +820,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_conn *conn)
 		union epoll_ref ref = { .r.proto = IPPROTO_TCP,
 					.r.s = conn->sock,
 					.r.p.tcp.tcp.timer = 1,
-					.r.p.tcp.tcp.index = conn - tc };
+					.r.p.tcp.tcp.index = CONN_IDX(conn) };
 		struct epoll_event ev = { .data.u64 = ref.u64,
 					  .events = EPOLLIN | EPOLLET };
 		int fd;
@@ -846,7 +853,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_conn *conn)
 		it.it_value.tv_sec = ACT_TIMEOUT;
 	}
 
-	debug("TCP: index %li, timer expires in %lu.%03lus", conn - tc,
+	debug("TCP: index %li, timer expires in %lu.%03lus", CONN_IDX(conn),
 	      it.it_value.tv_sec, it.it_value.tv_nsec / 1000 / 1000);
 
 	timerfd_settime(conn->timer, 0, &it, NULL);
@@ -867,7 +874,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_conn *conn,
 
 		conn->flags &= flag;
 		if (fls(~flag) >= 0) {
-			debug("TCP: index %li: %s dropped", conn - tc,
+			debug("TCP: index %li: %s dropped", CONN_IDX(conn),
 			      tcp_flag_str[fls(~flag)]);
 		}
 	} else {
@@ -876,7 +883,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_conn *conn,
 
 		conn->flags |= flag;
 		if (fls(flag) >= 0) {
-			debug("TCP: index %li: %s", conn - tc,
+			debug("TCP: index %li: %s", CONN_IDX(conn),
 			      tcp_flag_str[fls(flag)]);
 		}
 	}
@@ -926,12 +933,12 @@ static void conn_event_do(const struct ctx *c, struct tcp_conn *conn,
 		new += 5;
 
 	if (prev != new) {
-		debug("TCP: index %li, %s: %s -> %s", conn - tc,
+		debug("TCP: index %li, %s: %s -> %s", CONN_IDX(conn),
 		      num == -1 	       ? "CLOSED" : tcp_event_str[num],
 		      prev == -1	       ? "CLOSED" : tcp_state_str[prev],
 		      (new == -1 || num == -1) ? "CLOSED" : tcp_state_str[new]);
 	} else {
-		debug("TCP: index %li, %s", conn - tc,
+		debug("TCP: index %li, %s", CONN_IDX(conn),
 		      num == -1 	       ? "CLOSED" : tcp_event_str[num]);
 	}
 
@@ -1355,12 +1362,12 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_conn *conn,
 	int b;
 
 	b = tcp_hash(c, af, addr, conn->tap_port, conn->sock_port);
-	conn->next_index = tc_hash[b] ? tc_hash[b] - tc : -1;
+	conn->next_index = tc_hash[b] ? CONN_IDX(tc_hash[b]) : -1;
 	tc_hash[b] = conn;
 	conn->hash_bucket = b;
 
 	debug("TCP: hash table insert: index %li, sock %i, bucket: %i, next: "
-	      "%p", conn - tc, conn->sock, b, CONN_OR_NULL(conn->next_index));
+	      "%p", CONN_IDX(conn), conn->sock, b, conn_at_idx(conn->next_index));
 }
 
 /**
@@ -1373,19 +1380,19 @@ static void tcp_hash_remove(const struct tcp_conn *conn)
 	int b = conn->hash_bucket;
 
 	for (entry = tc_hash[b]; entry;
-	     prev = entry, entry = CONN_OR_NULL(entry->next_index)) {
+	     prev = entry, entry = conn_at_idx(entry->next_index)) {
 		if (entry == conn) {
 			if (prev)
 				prev->next_index = conn->next_index;
 			else
-				tc_hash[b] = CONN_OR_NULL(conn->next_index);
+				tc_hash[b] = conn_at_idx(conn->next_index);
 			break;
 		}
 	}
 
 	debug("TCP: hash table remove: index %li, sock %i, bucket: %i, new: %p",
-	      conn - tc, conn->sock, b,
-	      prev ? CONN_OR_NULL(prev->next_index) : tc_hash[b]);
+	      CONN_IDX(conn), conn->sock, b,
+	      prev ? conn_at_idx(prev->next_index) : tc_hash[b]);
 }
 
 /**
@@ -1399,10 +1406,10 @@ static void tcp_hash_update(struct tcp_conn *old, struct tcp_conn *new)
 	int b = old->hash_bucket;
 
 	for (entry = tc_hash[b]; entry;
-	     prev = entry, entry = CONN_OR_NULL(entry->next_index)) {
+	     prev = entry, entry = conn_at_idx(entry->next_index)) {
 		if (entry == old) {
 			if (prev)
-				prev->next_index = new - tc;
+				prev->next_index = CONN_IDX(new);
 			else
 				tc_hash[b] = new;
 			break;
@@ -1411,7 +1418,7 @@ static void tcp_hash_update(struct tcp_conn *old, struct tcp_conn *new)
 
 	debug("TCP: hash table update: old index %li, new index %li, sock %i, "
 	      "bucket: %i, old: %p, new: %p",
-	      old - tc, new - tc, new->sock, b, old, new);
+	      CONN_IDX(old), CONN_IDX(new), new->sock, b, old, new);
 }
 
 /**
@@ -1431,7 +1438,7 @@ static struct tcp_conn *tcp_hash_lookup(const struct ctx *c, int af,
 	int b = tcp_hash(c, af, addr, tap_port, sock_port);
 	struct tcp_conn *conn;
 
-	for (conn = tc_hash[b]; conn; conn = CONN_OR_NULL(conn->next_index)) {
+	for (conn = tc_hash[b]; conn; conn = conn_at_idx(conn->next_index)) {
 		if (tcp_hash_match(conn, af, addr, tap_port, sock_port))
 			return conn;
 	}
@@ -1448,9 +1455,9 @@ static void tcp_table_compact(struct ctx *c, struct tcp_conn *hole)
 {
 	struct tcp_conn *from, *to;
 
-	if ((hole - tc) == --c->tcp.conn_count) {
+	if (CONN_IDX(hole) == --c->tcp.conn_count) {
 		debug("TCP: hash table compaction: maximum index was %li (%p)",
-		      hole - tc, hole);
+		      CONN_IDX(hole), hole);
 		memset(hole, 0, sizeof(*hole));
 		return;
 	}
@@ -1465,7 +1472,7 @@ static void tcp_table_compact(struct ctx *c, struct tcp_conn *hole)
 
 	debug("TCP: hash table compaction: old index %li, new index %li, "
 	      "sock %i, from: %p, to: %p",
-	      from - tc, to - tc, from->sock, from, to);
+	      CONN_IDX(from), CONN_IDX(to), from->sock, from, to);
 
 	memset(from, 0, sizeof(*from));
 }
@@ -1488,7 +1495,7 @@ static void tcp_conn_destroy(struct ctx *c, struct tcp_conn *conn)
 static void tcp_rst_do(struct ctx *c, struct tcp_conn *conn);
 #define tcp_rst(c, conn)						\
 	do {								\
-		debug("TCP: index %li, reset at %s:%i", conn - tc,	\
+		debug("TCP: index %li, reset at %s:%i", CONN_IDX(conn), \
 		      __func__, __LINE__);				\
 		tcp_rst_do(c, conn);					\
 	} while (0)
@@ -2734,7 +2741,7 @@ int tcp_tap_handler(struct ctx *c, int af, const void *addr,
 		return 1;
 	}
 
-	trace("TCP: packet length %lu from tap for index %lu", len, conn - tc);
+	trace("TCP: packet length %lu from tap for index %lu", len, CONN_IDX(conn));
 
 	if (th->rst) {
 		conn_event(c, conn, CLOSED);
@@ -2942,7 +2949,7 @@ static void tcp_conn_from_sock(struct ctx *c, union epoll_ref ref,
  */
 static void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 {
-	struct tcp_conn *conn = CONN_OR_NULL(ref.r.p.tcp.tcp.index);
+	struct tcp_conn *conn = conn_at_idx(ref.r.p.tcp.tcp.index);
 	struct itimerspec check_armed = { { 0 }, { 0 } };
 
 	if (!conn)
@@ -2961,17 +2968,17 @@ static void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 		conn_flag(c, conn, ~ACK_TO_TAP_DUE);
 	} else if (conn->flags & ACK_FROM_TAP_DUE) {
 		if (!(conn->events & ESTABLISHED)) {
-			debug("TCP: index %li, handshake timeout", conn - tc);
+			debug("TCP: index %li, handshake timeout", CONN_IDX(conn));
 			tcp_rst(c, conn);
 		} else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) {
-			debug("TCP: index %li, FIN timeout", conn - tc);
+			debug("TCP: index %li, FIN timeout", CONN_IDX(conn));
 			tcp_rst(c, conn);
 		} else if (conn->retrans == TCP_MAX_RETRANS) {
 			debug("TCP: index %li, retransmissions count exceeded",
-			      conn - tc);
+			      CONN_IDX(conn));
 			tcp_rst(c, conn);
 		} else {
-			debug("TCP: index %li, ACK timeout, retry", conn - tc);
+			debug("TCP: index %li, ACK timeout, retry", CONN_IDX(conn));
 			conn->retrans++;
 			conn->seq_to_tap = conn->seq_ack_from_tap;
 			tcp_data_from_sock(c, conn);
@@ -2989,7 +2996,7 @@ static void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 		 */
 		timerfd_settime(conn->timer, 0, &new, &old);
 		if (old.it_value.tv_sec == ACT_TIMEOUT) {
-			debug("TCP: index %li, activity timeout", conn - tc);
+			debug("TCP: index %li, activity timeout", CONN_IDX(conn));
 			tcp_rst(c, conn);
 		}
 	}
@@ -3022,7 +3029,7 @@ void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events,
 		return;
 	}
 
-	if (!(conn = CONN_OR_NULL(ref.r.p.tcp.tcp.index)))
+	if (!(conn = conn_at_idx(ref.r.p.tcp.tcp.index)))
 		return;
 
 	if (conn->events == CLOSED)