tcp, udp, util: Enforce 24-bit limit on socket numbers

This should never happen, but there are no formal guarantees: ensure
socket numbers are below SOCKET_MAX.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

passt.h

@@ -45,7 +45,9 @@ union epoll_ref;
 union epoll_ref {
 	struct {
 		int32_t		proto:8,
-				s:24;
+#define SOCKET_REF_BITS		24
+#define SOCKET_MAX		(1 << SOCKET_REF_BITS)
+				s:SOCKET_REF_BITS;
 		union {
 			union tcp_epoll_ref tcp;
 			union udp_epoll_ref udp;

tcp.c

@@ -1971,6 +1971,11 @@ static int tcp_conn_new_sock(struct ctx *c, sa_family_t af)
 	if (s < 0)
 		s = socket(af, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);
 
+	if (s > SOCKET_MAX) {
+		close(s);
+		return -EIO;
+	}
+
 	if (s < 0)
 		return -errno;
 
@@ -2982,6 +2987,12 @@ static int tcp_sock_refill(void *arg)
 			break;
 		}
 		*p4 = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);
+		if (*p4 > SOCKET_MAX) {
+			close(*p4);
+			*p4 = -1;
+			return -EIO;
+		}
+
 		tcp_sock_set_bufsize(a->c, *p4);
 	}
 
@@ -2991,6 +3002,12 @@ static int tcp_sock_refill(void *arg)
 		}
 		*p6 = socket(AF_INET6, SOCK_STREAM | SOCK_NONBLOCK,
 			     IPPROTO_TCP);
+		if (*p6 > SOCKET_MAX) {
+			close(*p6);
+			*p6 = -1;
+			return -EIO;
+		}
+
 		tcp_sock_set_bufsize(a->c, *p6);
 	}
 

tcp_splice.c

@@ -418,6 +418,14 @@ static int tcp_splice_connect(struct ctx *c, struct tcp_splice_conn *conn,
 	const struct sockaddr *sa;
 	socklen_t sl;
 
+	if (sock_conn < 0)
+		return -errno;
+
+	if (sock_conn > SOCKET_MAX) {
+		close(sock_conn);
+		return -EIO;
+	}
+
 	conn->b = sock_conn;
 
 	if (s < 0)

udp.c

@@ -443,8 +443,15 @@ int udp_splice_connect(struct ctx *c, int v6, int bound_sock,
 
 	s = socket(v6 ? AF_INET6 : AF_INET, SOCK_DGRAM | SOCK_NONBLOCK,
 		   IPPROTO_UDP);
+
+	if (s > SOCKET_MAX) {
+		close(s);
+		return -EIO;
+	}
+
 	if (s < 0)
 		return s;
+
 	ref.r.s = s;
 
 	if (v6) {

util.c

@@ -235,10 +235,17 @@ int sock_l4(struct ctx *c, int af, uint8_t proto, uint16_t port,
 		fd = socket(af, SOCK_STREAM | SOCK_NONBLOCK, proto);
 	else
 		fd = socket(af, SOCK_DGRAM | SOCK_NONBLOCK, proto);
+
 	if (fd < 0) {
 		perror("L4 socket");
 		return -1;
 	}
+
+	if (fd > SOCKET_MAX) {
+		close(fd);
+		return -EIO;
+	}
+
 	ref.r.s = fd;
 
 	if (af == AF_INET) {