net: sockets: tls: Fix handshake on non blocking sockets

The TLS/DTLS handshake in most cases is a blocking process, therefore
the underlying socket should be in a blocking mode to prevent busy
looping in the handshake thread. Fix this by clearing the O_NONBLOCK
flag on the underlying socket before the handshake, and restoring it
afterards.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

subsys/net/lib/sockets/sockets_tls.c

@@ -820,6 +820,20 @@ static int tls_mbedtls_reset(struct tls_context *context)
 static int tls_mbedtls_handshake(struct tls_context *context, bool block)
 {
 	int ret;
+	int sock_flags;
+
+	sock_flags = zsock_fcntl(context->sock, F_GETFL, 0);
+	if (sock_flags < 0) {
+		return -EIO;
+	}
+
+	if (block && sock_flags & O_NONBLOCK) {
+		/* Clear the O_NONBLOCK flag for the handshake to prevent busy
+		 * looping in the handshake thread.
+		 */
+		(void)zsock_fcntl(context->sock, F_SETFL,
+				  sock_flags & ~O_NONBLOCK);
+	}
 
 	while ((ret = mbedtls_ssl_handshake(&context->ssl)) != 0) {
 		if (ret == MBEDTLS_ERR_SSL_WANT_READ ||
@@ -847,6 +861,10 @@ static int tls_mbedtls_handshake(struct tls_context *context, bool block)
 		break;
 	}
 
+	if (block && sock_flags & O_NONBLOCK) {
+		(void)zsock_fcntl(context->sock, F_SETFL, sock_flags);
+	}
+
 	if (ret == 0) {
 		k_sem_give(&context->tls_established);
 	}